Merge branch 'refactor-relaycache'

11 files changed, 548 insertions, 411 deletions

diff --git a/ios/MullvadVPN.xcodeproj/project.pbxproj b/ios/MullvadVPN.xcodeproj/project.pbxproj
index 843362f450..a561a860af 100644
--- a/ios/MullvadVPN.xcodeproj/project.pbxproj
+++ b/ios/MullvadVPN.xcodeproj/project.pbxproj
@@ -30,9 +30,13 @@
 		5823FA5026CA690600283BF8 /* OSLogHandler.swift in Sources */ = {isa = PBXBuildFile; fileRef = 5823FA4F26CA690600283BF8 /* OSLogHandler.swift */; };
 		5820674E26E6510200655B05 /* REST.swift in Sources */ = {isa = PBXBuildFile; fileRef = 5820674D26E6510200655B05 /* REST.swift */; };
 		5820675026E6514100655B05 /* HTTP.swift in Sources */ = {isa = PBXBuildFile; fileRef = 5820674F26E6514100655B05 /* HTTP.swift */; };
+		5820675526E6528200655B05 /* RelayCacheError.swift in Sources */ = {isa = PBXBuildFile; fileRef = 585DA87926B024F900B8C587 /* RelayCacheError.swift */; };
 		5820675626E6528A00655B05 /* RESTError.swift in Sources */ = {isa = PBXBuildFile; fileRef = 585DA88626B0277200B8C587 /* RESTError.swift */; };
 		5820675726E652A600655B05 /* REST.swift in Sources */ = {isa = PBXBuildFile; fileRef = 5820674D26E6510200655B05 /* REST.swift */; };
+		5820675826E652AF00655B05 /* RelayCacheIO.swift in Sources */ = {isa = PBXBuildFile; fileRef = 585DA87C26B0254000B8C587 /* RelayCacheIO.swift */; };
 		5820675926E652BE00655B05 /* RESTCoding.swift in Sources */ = {isa = PBXBuildFile; fileRef = 585DA88926B027A300B8C587 /* RESTCoding.swift */; };
+		5820675B26E6576800655B05 /* RelayCache.swift in Sources */ = {isa = PBXBuildFile; fileRef = 5820675A26E6576800655B05 /* RelayCache.swift */; };
+		5820675C26E6576800655B05 /* RelayCache.swift in Sources */ = {isa = PBXBuildFile; fileRef = 5820675A26E6576800655B05 /* RelayCache.swift */; };
 		5820675E26E6839900655B05 /* PresentAlertOperation.swift in Sources */ = {isa = PBXBuildFile; fileRef = 5820675D26E6839900655B05 /* PresentAlertOperation.swift */; };
 		5820676226E75D8500655B05 /* REST.swift in Sources */ = {isa = PBXBuildFile; fileRef = 5820674D26E6510200655B05 /* REST.swift */; };
 		58293FAE2510CA58005D0BB5 /* ProblemReportViewController.swift in Sources */ = {isa = PBXBuildFile; fileRef = 58293FAC2510CA58005D0BB5 /* ProblemReportViewController.swift */; };
@@ -91,6 +95,10 @@
 		585834F824D2BC1F00A8AF56 /* Logging in Frameworks */ = {isa = PBXBuildFile; productRef = 585834F724D2BC1F00A8AF56 /* Logging */; };
 		585834FC24D2BC9500A8AF56 /* Logging in Frameworks */ = {isa = PBXBuildFile; productRef = 585834FB24D2BC9500A8AF56 /* Logging */; };
 		585CA70F25F8C44600B47C62 /* UIMetrics.swift in Sources */ = {isa = PBXBuildFile; fileRef = 585CA70E25F8C44600B47C62 /* UIMetrics.swift */; };
+		585DA87726B024A600B8C587 /* CachedRelays.swift in Sources */ = {isa = PBXBuildFile; fileRef = 585DA87626B024A600B8C587 /* CachedRelays.swift */; };
+		585DA87826B024A900B8C587 /* CachedRelays.swift in Sources */ = {isa = PBXBuildFile; fileRef = 585DA87626B024A600B8C587 /* CachedRelays.swift */; };
+		585DA87A26B024F900B8C587 /* RelayCacheError.swift in Sources */ = {isa = PBXBuildFile; fileRef = 585DA87926B024F900B8C587 /* RelayCacheError.swift */; };
+		585DA87D26B0254000B8C587 /* RelayCacheIO.swift in Sources */ = {isa = PBXBuildFile; fileRef = 585DA87C26B0254000B8C587 /* RelayCacheIO.swift */; };
 		585DA88426B0270700B8C587 /* ServerRelaysResponse.swift in Sources */ = {isa = PBXBuildFile; fileRef = 585DA88326B0270700B8C587 /* ServerRelaysResponse.swift */; };
 		585DA88526B0270700B8C587 /* ServerRelaysResponse.swift in Sources */ = {isa = PBXBuildFile; fileRef = 585DA88326B0270700B8C587 /* ServerRelaysResponse.swift */; };
 		585DA88726B0277200B8C587 /* RESTError.swift in Sources */ = {isa = PBXBuildFile; fileRef = 585DA88626B0277200B8C587 /* RESTError.swift */; };
@@ -181,8 +189,7 @@
 		58BA791B2578F092006FAEA0 /* WireGuardKit in Frameworks */ = {isa = PBXBuildFile; productRef = 58BA791A2578F092006FAEA0 /* WireGuardKit */; };
 		58BA7947257901A5006FAEA0 /* WireGuardKit in Frameworks */ = {isa = PBXBuildFile; productRef = 58BA7946257901A5006FAEA0 /* WireGuardKit */; };
 		58BF345E26F09F3C002A6CAA /* ExclusivityController.swift in Sources */ = {isa = PBXBuildFile; fileRef = 580EE20524B3222200F9D8A1 /* ExclusivityController.swift */; };
-		58BFA5C622A7C97F00A6173D /* RelayCache.swift in Sources */ = {isa = PBXBuildFile; fileRef = 58BFA5C522A7C97F00A6173D /* RelayCache.swift */; };
-		58BFA5C722A7C97F00A6173D /* RelayCache.swift in Sources */ = {isa = PBXBuildFile; fileRef = 58BFA5C522A7C97F00A6173D /* RelayCache.swift */; };
+		58BFA5C622A7C97F00A6173D /* RelayCacheTracker.swift in Sources */ = {isa = PBXBuildFile; fileRef = 58BFA5C522A7C97F00A6173D /* RelayCacheTracker.swift */; };
 		58BFA5CC22A7CE1F00A6173D /* ApplicationConfiguration.swift in Sources */ = {isa = PBXBuildFile; fileRef = 58BFA5CB22A7CE1F00A6173D /* ApplicationConfiguration.swift */; };
 		58BFA5CD22A7CE1F00A6173D /* ApplicationConfiguration.swift in Sources */ = {isa = PBXBuildFile; fileRef = 58BFA5CB22A7CE1F00A6173D /* ApplicationConfiguration.swift */; };
 		58C3478B26C1094F0060838B /* Promise.swift in Sources */ = {isa = PBXBuildFile; fileRef = 585DA8AE26B9492500B8C587 /* Promise.swift */; };
@@ -269,6 +276,8 @@
 		58FB865526E8BF3100F188BC /* AppStorePaymentManagerError.swift in Sources */ = {isa = PBXBuildFile; fileRef = 58FB865426E8BF3100F188BC /* AppStorePaymentManagerError.swift */; };
 		58FB865E26EA284E00F188BC /* LogFormatting.swift in Sources */ = {isa = PBXBuildFile; fileRef = 58FB865D26EA284E00F188BC /* LogFormatting.swift */; };
 		58FB865F26EA2E6D00F188BC /* LogFormatting.swift in Sources */ = {isa = PBXBuildFile; fileRef = 58FB865D26EA284E00F188BC /* LogFormatting.swift */; };
+		58FB865826EA213300F188BC /* AnyRelayCacheObserver.swift in Sources */ = {isa = PBXBuildFile; fileRef = 58FB865726EA213300F188BC /* AnyRelayCacheObserver.swift */; };
+		58FB865A26EA214400F188BC /* RelayCacheObserver.swift in Sources */ = {isa = PBXBuildFile; fileRef = 58FB865926EA214400F188BC /* RelayCacheObserver.swift */; };
 		58FD5BE724192A2C00112C88 /* AppStoreReceipt.swift in Sources */ = {isa = PBXBuildFile; fileRef = 58FD5BE624192A2B00112C88 /* AppStoreReceipt.swift */; };
 		58FD5BF024238EB300112C88 /* SKProduct+Formatting.swift in Sources */ = {isa = PBXBuildFile; fileRef = 58FD5BEF24238EB300112C88 /* SKProduct+Formatting.swift */; };
 		58FD5BF22424F7D700112C88 /* UserInterfaceInteractionRestriction.swift in Sources */ = {isa = PBXBuildFile; fileRef = 58FD5BF12424F7D700112C88 /* UserInterfaceInteractionRestriction.swift */; };
@@ -338,6 +347,7 @@
 		5820674826E63EC800655B05 /* Promise+BackgroundTask.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = "Promise+BackgroundTask.swift"; sourceTree = "<group>"; };
 		5820674D26E6510200655B05 /* REST.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = REST.swift; sourceTree = "<group>"; };
 		5820674F26E6514100655B05 /* HTTP.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = HTTP.swift; sourceTree = "<group>"; };
+		5820675A26E6576800655B05 /* RelayCache.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = RelayCache.swift; sourceTree = "<group>"; };
 		5820675D26E6839900655B05 /* PresentAlertOperation.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = PresentAlertOperation.swift; sourceTree = "<group>"; };
 		5823FA4F26CA690600283BF8 /* OSLogHandler.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = OSLogHandler.swift; sourceTree = "<group>"; };
 		58293FAC2510CA58005D0BB5 /* ProblemReportViewController.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = ProblemReportViewController.swift; sourceTree = "<group>"; };
@@ -375,6 +385,9 @@
 		5857F24224C8662600CF6F47 /* SelectLocationHeaderView.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = SelectLocationHeaderView.swift; sourceTree = "<group>"; };
 		5857F24624C882D700CF6F47 /* SelectLocationNavigationController.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = SelectLocationNavigationController.swift; sourceTree = "<group>"; };
 		585CA70E25F8C44600B47C62 /* UIMetrics.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = UIMetrics.swift; sourceTree = "<group>"; };
+		585DA87626B024A600B8C587 /* CachedRelays.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = CachedRelays.swift; sourceTree = "<group>"; };
+		585DA87926B024F900B8C587 /* RelayCacheError.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = RelayCacheError.swift; sourceTree = "<group>"; };
+		585DA87C26B0254000B8C587 /* RelayCacheIO.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = RelayCacheIO.swift; sourceTree = "<group>"; };
 		585DA88326B0270700B8C587 /* ServerRelaysResponse.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = ServerRelaysResponse.swift; sourceTree = "<group>"; };
 		585DA88626B0277200B8C587 /* RESTError.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = RESTError.swift; sourceTree = "<group>"; };
 		585DA88926B027A300B8C587 /* RESTCoding.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = RESTCoding.swift; sourceTree = "<group>"; };
@@ -435,7 +448,7 @@
 		58B9EB142489139B00095626 /* DisplayChainedError.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = DisplayChainedError.swift; sourceTree = "<group>"; };
 		58BA692D23E99EFF009DC256 /* Locking.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = Locking.swift; sourceTree = "<group>"; };
 		58BA693023EADA6A009DC256 /* SimulatorTunnelProvider.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = SimulatorTunnelProvider.swift; sourceTree = "<group>"; };
-		58BFA5C522A7C97F00A6173D /* RelayCache.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = RelayCache.swift; sourceTree = "<group>"; };
+		58BFA5C522A7C97F00A6173D /* RelayCacheTracker.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = RelayCacheTracker.swift; sourceTree = "<group>"; };
 		58BFA5CB22A7CE1F00A6173D /* ApplicationConfiguration.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = ApplicationConfiguration.swift; sourceTree = "<group>"; };
 		58C3A4B122456F1A00340BDB /* AccountInputGroupView.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = AccountInputGroupView.swift; sourceTree = "<group>"; };
 		58C6B35322BB87C4003C19AD /* PrivateKeyWithMetadata.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = PrivateKeyWithMetadata.swift; sourceTree = "<group>"; };
@@ -503,6 +516,8 @@
 		58FAEE0024533A9C00CB0F5B /* KeychainClass.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = KeychainClass.swift; sourceTree = "<group>"; };
 		58FB865426E8BF3100F188BC /* AppStorePaymentManagerError.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = AppStorePaymentManagerError.swift; sourceTree = "<group>"; };
 		58FB865D26EA284E00F188BC /* LogFormatting.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = LogFormatting.swift; sourceTree = "<group>"; };
+		58FB865726EA213300F188BC /* AnyRelayCacheObserver.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = AnyRelayCacheObserver.swift; sourceTree = "<group>"; };
+		58FB865926EA214400F188BC /* RelayCacheObserver.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = RelayCacheObserver.swift; sourceTree = "<group>"; };
 		58FD5BE624192A2B00112C88 /* AppStoreReceipt.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = AppStoreReceipt.swift; sourceTree = "<group>"; };
 		58FD5BEF24238EB300112C88 /* SKProduct+Formatting.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = "SKProduct+Formatting.swift"; sourceTree = "<group>"; };
 		58FD5BF12424F7D700112C88 /* UserInterfaceInteractionRestriction.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = UserInterfaceInteractionRestriction.swift; sourceTree = "<group>"; };
@@ -613,6 +628,20 @@
 			path = MullvadVPN;
 			sourceTree = "<group>";
 		};
+		585DA87526B0249A00B8C587 /* RelayCache */ = {
+			isa = PBXGroup;
+			children = (
+				58FB865726EA213300F188BC /* AnyRelayCacheObserver.swift */,
+				585DA87626B024A600B8C587 /* CachedRelays.swift */,
+				5820675A26E6576800655B05 /* RelayCache.swift */,
+				585DA87926B024F900B8C587 /* RelayCacheError.swift */,
+				585DA87C26B0254000B8C587 /* RelayCacheIO.swift */,
+				58FB865926EA214400F188BC /* RelayCacheObserver.swift */,
+				58BFA5C522A7C97F00A6173D /* RelayCacheTracker.swift */,
+			);
+			path = RelayCache;
+			sourceTree = "<group>";
+		};
 		585DA87F26B0268500B8C587 /* REST */ = {
 			isa = PBXGroup;
 			children = (
@@ -771,7 +800,7 @@
 				58F8AC0D25D3F8CE002BE0ED /* ProblemReportReviewViewController.swift */,
 				58EF580A25D69D7A00AEBA94 /* ProblemReportSubmissionOverlayView.swift */,
 				58293FAC2510CA58005D0BB5 /* ProblemReportViewController.swift */,
-				58BFA5C522A7C97F00A6173D /* RelayCache.swift */,
+				585DA87526B0249A00B8C587 /* RelayCache */,
 				58781CC822AE7CA8009B9D8E /* RelayConstraints.swift */,
 				58781CD422AFBA39009B9D8E /* RelaySelector.swift */,
 				585DA87F26B0268500B8C587 /* REST */,
@@ -1176,6 +1205,8 @@
 				5846227126E229F20035F7C2 /* AppStoreSubscription.swift in Sources */,
 				58E1337126D2BE9C00CC316B /* AnyOptional.swift in Sources */,
 				5846226526E0D9630035F7C2 /* ProductsRequestOperation.swift in Sources */,
+				5820675B26E6576800655B05 /* RelayCache.swift in Sources */,
+				585DA87D26B0254000B8C587 /* RelayCacheIO.swift in Sources */,
 				58BA693123EADA6A009DC256 /* SimulatorTunnelProvider.swift in Sources */,
 				58E1336D26D2BE7500CC316B /* AnyResult.swift in Sources */,
 				587B753B2666467500DEF7E9 /* NotificationBannerView.swift in Sources */,
@@ -1187,7 +1218,8 @@
 				585DA88426B0270700B8C587 /* ServerRelaysResponse.swift in Sources */,
 				58F8AC0E25D3F8CE002BE0ED /* ProblemReportReviewViewController.swift in Sources */,
 				58CCA010224249A1004F3011 /* ConnectViewController.swift in Sources */,
-				58BFA5C622A7C97F00A6173D /* RelayCache.swift in Sources */,
+				58BFA5C622A7C97F00A6173D /* RelayCacheTracker.swift in Sources */,
+				58BFA5C622A7C97F00A6173D /* RelayCacheTracker.swift in Sources */,
 				582BB1B1229569620055B6EF /* CustomNavigationBar.swift in Sources */,
 				584789E026529D72000E45FB /* SSLPinningURLSessionDelegate.swift in Sources */,
 				58ACF6492655365700ACE4B7 /* PreferencesViewController.swift in Sources */,
@@ -1196,12 +1228,14 @@
 				5820675026E6514100655B05 /* HTTP.swift in Sources */,
 				5877153023981F7B001F8237 /* WireguardKeysViewController.swift in Sources */,
 				587B7536266528A200DEF7E9 /* NotificationManager.swift in Sources */,
+				58FB865A26EA214400F188BC /* RelayCacheObserver.swift in Sources */,
 				58ACF64D26567A5000ACE4B7 /* CustomSwitch.swift in Sources */,
 				5850367F25A481D800A43E93 /* IPAddressRange+Codable.swift in Sources */,
 				5871FB96254ADE4E0051A0A4 /* ConsolidatedApplicationLog.swift in Sources */,
 				58FEEB58260B662E00A621A8 /* AutomaticKeyboardResponder.swift in Sources */,
 				5846227326E22A160035F7C2 /* AppStorePaymentObserver.swift in Sources */,
 				58FAEDEF245069C700CB0F5B /* KeychainAttributes.swift in Sources */,
+				585DA87A26B024F900B8C587 /* RelayCacheError.swift in Sources */,
 				58CB0EE024B86751001EF0D8 /* RESTClient.swift in Sources */,
 				5846226A26E0E6FA0035F7C2 /* ReceiptRefreshOperation.swift in Sources */,
 				58E1337526D2BEC400CC316B /* Promise+Optional.swift in Sources */,
@@ -1287,6 +1321,8 @@
 				585DA88726B0277200B8C587 /* RESTError.swift in Sources */,
 				58293FB725138B88005D0BB5 /* CustomNavigationController.swift in Sources */,
 				587425C12299833500CA2045 /* RootContainerViewController.swift in Sources */,
+				585DA87726B024A600B8C587 /* CachedRelays.swift in Sources */,
+				58FB865826EA213300F188BC /* AnyRelayCacheObserver.swift in Sources */,
 				5896AE84246D5889005B36CB /* CustomDateComponentsFormatting.swift in Sources */,
 				587AD7C623421D7000E93A53 /* TunnelSettings.swift in Sources */,
 				581503A324D6F1EC00C9C50E /* ChainedError+Logger.swift in Sources */,
@@ -1321,6 +1357,7 @@
 				5850368D25A49E2200A43E93 /* PrivateKeyWithMetadata.swift in Sources */,
 				580EE20724B3222400F9D8A1 /* ExclusivityController.swift in Sources */,
 				58F840B02464382C0044E708 /* KeychainItemRevision.swift in Sources */,
+				5820675826E652AF00655B05 /* RelayCacheIO.swift in Sources */,
 				5820675726E652A600655B05 /* REST.swift in Sources */,
 				58E1337A26D2BEDD00CC316B /* Promise+ReceiveOn.swift in Sources */,
 				58B93A2526C683B300A55733 /* Promise.swift in Sources */,
@@ -1330,6 +1367,7 @@
 				58AEEF662344A37400C9BBD5 /* KeychainError.swift in Sources */,
 				5840250222B1124600E4CFEC /* IPAddress+Codable.swift in Sources */,
 				58BA693223EAE1AE009DC256 /* SimulatorTunnelProvider.swift in Sources */,
+				5820675C26E6576800655B05 /* RelayCache.swift in Sources */,
 				58CE5E7C224146470008646E /* PacketTunnelProvider.swift in Sources */,
 				58FAEDF1245069CA00CB0F5B /* KeychainAttributes.swift in Sources */,
 				586AA296234B696B00502875 /* WireguardAssociatedAddresses.swift in Sources */,
@@ -1347,14 +1385,15 @@
 				5815039824D6ECAE00C9C50E /* CustomFormatLogHandler.swift in Sources */,
 				5840250522B11AB700E4CFEC /* MullvadEndpoint.swift in Sources */,
 				583BC70824FE4DC500C9DE04 /* Optional+DispatchQueue.swift in Sources */,
-				58BFA5C722A7C97F00A6173D /* RelayCache.swift in Sources */,
 				58906DE02445C7A5002F0673 /* NEProviderStopReason+Debug.swift in Sources */,
 				5815039E24D6ECE600C9C50E /* TextFileOutputStream.swift in Sources */,
+				585DA87826B024A900B8C587 /* CachedRelays.swift in Sources */,
 				584E96BD240FD4DA00D3334F /* Location.swift in Sources */,
 				58FAEDF8245088E100CB0F5B /* Keychain.swift in Sources */,
 				58F840B32464491D0044E708 /* ChainedError.swift in Sources */,
 				58D67A0A26D7AE3300557C3C /* OSLogHandler.swift in Sources */,
 				5820675626E6528A00655B05 /* RESTError.swift in Sources */,
+				5820675526E6528200655B05 /* RelayCacheError.swift in Sources */,
 				58561C9A239A5D1500BD6B5E /* IPEndpoint.swift in Sources */,
 				588534BF246193D90018B744 /* AutomaticKeyRotationManager.swift in Sources */,
 				58E1337626D2BEC400CC316B /* Promise+Optional.swift in Sources */,
diff --git a/ios/MullvadVPN/AppDelegate.swift b/ios/MullvadVPN/AppDelegate.swift
index c240b4ddf0..fcbc2542ae 100644
--- a/ios/MullvadVPN/AppDelegate.swift
+++ b/ios/MullvadVPN/AppDelegate.swift
@@ -32,7 +32,7 @@ class AppDelegate: UIResponder, UIApplicationDelegate {
     private var connectController: ConnectViewController?
     private weak var settingsNavController: SettingsNavigationController?
 
-    private var cachedRelays: CachedRelays? {
+    private var cachedRelays: RelayCache.CachedRelays? {
         didSet {
             if let cachedRelays = cachedRelays {
                 self.selectLocationViewController?.setCachedRelays(cachedRelays)
@@ -75,23 +75,22 @@ class AppDelegate: UIResponder, UIApplicationDelegate {
         launchController.view.backgroundColor = .primaryColor
         self.window?.rootViewController = launchController
 
-        // Update relays
-        RelayCache.shared.addObserver(self)
-        RelayCache.shared.updateRelays()
+        // Add relay cache observer
+        RelayCache.Tracker.shared.addObserver(self)
 
         // Load initial relays
-        self.logger?.debug("Load relays")
-        RelayCache.shared.read { (result) in
-            DispatchQueue.main.async {
+        RelayCache.Tracker.shared.read()
+            .receive(on: .main)
+            .observe { completion in
+                guard let result = completion.unwrappedValue else { return }
+
                 switch result {
                 case .success(let cachedRelays):
                     self.cachedRelays = cachedRelays
-                    self.logger?.debug("Loaded relays")
 
                 case .failure(let error):
                     self.logger?.error(chainedError: error, message: "Failed to load initial relays")
                 }
-            }
         }
 
         // Load tunnels
@@ -134,6 +133,14 @@ class AppDelegate: UIResponder, UIApplicationDelegate {
 
     func applicationDidBecomeActive(_ application: UIApplication) {
         TunnelManager.shared.refreshTunnelState(completionHandler: nil)
+
+        // Start periodic relays updates
+        RelayCache.Tracker.shared.startPeriodicUpdates()
+    }
+
+    func applicationWillResignActive(_ application: UIApplication) {
+        // Stop periodic relays updates
+        RelayCache.Tracker.shared.stopPeriodicUpdates()
     }
 
     // MARK: - Private
@@ -701,7 +708,7 @@ extension AppDelegate: UIAdaptivePresentationControllerDelegate {
 
 extension AppDelegate: RelayCacheObserver {
 
-    func relayCache(_ relayCache: RelayCache, didUpdateCachedRelays cachedRelays: CachedRelays) {
+    func relayCache(_ relayCache: RelayCache.Tracker, didUpdateCachedRelays cachedRelays: RelayCache.CachedRelays) {
         DispatchQueue.main.async {
             self.cachedRelays = cachedRelays
         }
diff --git a/ios/MullvadVPN/RelayCache.swift b/ios/MullvadVPN/RelayCache.swift
deleted file mode 100644
index fe07798bbd..0000000000
--- a/ios/MullvadVPN/RelayCache.swift
+++ /dev/null
@@ -1,393 +0,0 @@
-//
-//  RelayCache.swift
-//  MullvadVPN
-//
-//  Created by pronebird on 05/06/2019.
-//  Copyright © 2019 Mullvad VPN AB. All rights reserved.
-//
-
-import Foundation
-import Logging
-
-/// Periodic update interval
-private let kUpdateIntervalSeconds = 3600
-
-/// Error emitted by read and write functions
-enum RelayCacheError: ChainedError {
-    case readCache(Error)
-    case readPrebundledRelays(Error)
-    case decodePrebundledRelays(Error)
-    case writeCache(Error)
-    case encodeCache(Error)
-    case decodeCache(Error)
-    case rest(RestError)
-
-    var errorDescription: String? {
-        switch self {
-        case .encodeCache:
-            return "Encode cache error"
-        case .decodeCache:
-            return "Decode cache error"
-        case .readCache:
-            return "Read cache error"
-        case .readPrebundledRelays:
-            return "Read pre-bundled relays error"
-        case .decodePrebundledRelays:
-            return "Decode pre-bundled relays error"
-        case .writeCache:
-            return "Write cache error"
-        case .rest:
-            return "REST error"
-        }
-    }
-}
-
-protocol RelayCacheObserver: AnyObject {
-    func relayCache(_ relayCache: RelayCache, didUpdateCachedRelays cachedRelays: CachedRelays)
-}
-
-private class AnyRelayCacheObserver: WeakObserverBox, RelayCacheObserver {
-
-    typealias Wrapped = RelayCacheObserver
-
-    private(set) weak var inner: RelayCacheObserver?
-
-    init<T: RelayCacheObserver>(_ inner: T) {
-        self.inner = inner
-    }
-
-    func relayCache(_ relayCache: RelayCache, didUpdateCachedRelays cachedRelays: CachedRelays) {
-        inner?.relayCache(relayCache, didUpdateCachedRelays: cachedRelays)
-    }
-
-    static func == (lhs: AnyRelayCacheObserver, rhs: AnyRelayCacheObserver) -> Bool {
-        return lhs.inner === rhs.inner
-    }
-}
-
-class RelayCache {
-    private let logger = Logger(label: "RelayCache")
-
-    /// Mullvad REST client
-    private let rest = MullvadRest()
-
-    /// The cache location used by the class instance
-    private let cacheFileURL: URL
-
-    /// A dispatch queue used for thread synchronization
-    private let dispatchQueue = DispatchQueue(label: "net.mullvad.MullvadVPN.RelayCache")
-
-    /// A timer source used for periodic updates
-    private var timerSource: DispatchSourceTimer?
-
-    /// A flag that indicates whether periodic updates are running
-    private var isPeriodicUpdatesEnabled = false
-
-    /// A download task used for relay RPC request
-    private var downloadTask: URLSessionTask?
-
-    /// The default cache file location
-    static var defaultCacheFileURL: URL {
-        let appGroupIdentifier = ApplicationConfiguration.securityGroupIdentifier
-        let containerURL = FileManager.default.containerURL(forSecurityApplicationGroupIdentifier: appGroupIdentifier)!
-
-        return containerURL.appendingPathComponent("relays.json")
-    }
-
-    /// The path to the pre-bundled relays.json file
-    private static var preBundledRelaysFileURL: URL {
-        return Bundle.main.url(forResource: "relays", withExtension: "json")!
-    }
-
-    /// Observers
-    private let observerList = ObserverList<AnyRelayCacheObserver>()
-
-    /// A shared instance of `RelayCache`
-    static let shared = RelayCache(cacheFileURL: defaultCacheFileURL)
-
-    private init(cacheFileURL: URL) {
-        self.cacheFileURL = cacheFileURL
-    }
-
-    func startPeriodicUpdates(queue: DispatchQueue?, completionHandler: (() -> Void)?) {
-        dispatchQueue.async {
-            if !self.isPeriodicUpdatesEnabled {
-                self.isPeriodicUpdatesEnabled = true
-
-                switch Self.read(cacheFileURL: self.cacheFileURL) {
-                case .success(let cachedRelayList):
-                    if let nextUpdate = Self.nextUpdateDate(lastUpdatedAt: cachedRelayList.updatedAt) {
-                        let startTime = Self.makeWalltime(fromDate: nextUpdate)
-                        self.scheduleRepeatingTimer(startTime: startTime)
-                    }
-
-                case .failure(let readError):
-                    self.logger.error(chainedError: readError, message: "Failed to read the relay cache")
-
-                    if Self.shouldDownloadRelaysOnReadFailure(readError) {
-                        self.scheduleRepeatingTimer(startTime: .now())
-                    }
-                }
-            }
-
-            queue.performOnWrappedOrCurrentQueue {
-                completionHandler?()
-            }
-        }
-    }
-
-    func stopPeriodicUpdates(queue: DispatchQueue?, completionHandler: (() -> Void)?) {
-        dispatchQueue.async {
-            self.isPeriodicUpdatesEnabled = false
-
-            self.timerSource?.cancel()
-            self.timerSource = nil
-            self.downloadTask?.cancel()
-
-            queue.performOnWrappedOrCurrentQueue {
-                completionHandler?()
-            }
-        }
-    }
-
-    func updateRelays() {
-        dispatchQueue.async {
-            self._updateRelays()
-        }
-    }
-
-    /// Read the relay cache from disk
-    func read(completionHandler: @escaping (Result<CachedRelays, RelayCacheError>) -> Void) {
-        dispatchQueue.async {
-            let result = Self.read(cacheFileURL: self.cacheFileURL)
-                .flatMapError { (error) -> Result<CachedRelays, RelayCacheError> in
-                    switch error {
-                    case .decodeCache, .readCache(CocoaError.fileReadNoSuchFile):
-                        return Self.readPrebundledRelays(fileURL: Self.preBundledRelaysFileURL)
-                    default:
-                        return .failure(error)
-                    }
-            }
-            completionHandler(result)
-        }
-    }
-
-    // MARK: - Observation
-
-    func addObserver<T: RelayCacheObserver>(_ observer: T) {
-        observerList.append(AnyRelayCacheObserver(observer))
-    }
-
-    func removeObserver<T: RelayCacheObserver>(_ observer: T) {
-        observerList.remove(AnyRelayCacheObserver(observer))
-    }
-
-    // MARK: - Private instance methods
-
-    private func _updateRelays() {
-        switch Self.read(cacheFileURL: self.cacheFileURL) {
-        case .success(let cachedRelays):
-            let nextUpdate = Self.nextUpdateDate(lastUpdatedAt: cachedRelays.updatedAt)
-
-            if let nextUpdate = nextUpdate, nextUpdate <= Date() {
-                self.downloadRelays(previouslyCachedRelays: cachedRelays)
-            }
-
-        case .failure(let readError):
-            self.logger.error(chainedError: readError, message: "Failed to read the relay cache to determine if it needs to be updated")
-
-            if Self.shouldDownloadRelaysOnReadFailure(readError) {
-                self.downloadRelays(previouslyCachedRelays: nil)
-            }
-        }
-    }
-
-    private func downloadRelays(previouslyCachedRelays: CachedRelays?) {
-        let taskResult = makeDownloadTask(etag: previouslyCachedRelays?.etag) { (result) in
-            switch result {
-            case .success(.newContent(let etag, let relays)):
-                let numRelays = relays.wireguard.relays.count
-
-                self.logger.info("Downloaded \(numRelays) relays")
-
-                let cachedRelays = CachedRelays(etag: etag, relays: relays, updatedAt: Date())
-                switch Self.write(cacheFileURL: self.cacheFileURL, record: cachedRelays) {
-                case .success:
-                    self.observerList.forEach { (observer) in
-                        observer.relayCache(self, didUpdateCachedRelays: cachedRelays)
-                    }
-
-                case .failure(let error):
-                    self.logger.error(chainedError: error, message: "Failed to store downloaded relays")
-                }
-
-            case .success(.notModified):
-                self.logger.info("Relays haven't changed since last check.")
-
-                var cachedRelays = previouslyCachedRelays!
-                cachedRelays.updatedAt = Date()
-
-                switch Self.write(cacheFileURL: self.cacheFileURL, record: cachedRelays) {
-                case .success:
-                    break
-
-                case .failure(let error):
-                    self.logger.error(chainedError: error, message: "Failed to update cached relays timestamp")
-                }
-
-            case .failure(let error):
-                self.logger.error(chainedError: error, message: "Failed to download relays")
-            }
-        }
-
-        downloadTask?.cancel()
-
-        switch taskResult {
-        case .success(let newDownloadTask):
-            downloadTask = newDownloadTask
-            newDownloadTask.resume()
-
-        case .failure(let restError):
-            self.logger.error(chainedError: restError, message: "Failed to create a REST request for updating relays")
-            downloadTask = nil
-        }
-    }
-
-    private func scheduleRepeatingTimer(startTime: DispatchWallTime) {
-        let timerSource = DispatchSource.makeTimerSource(queue: dispatchQueue)
-        timerSource.setEventHandler { [weak self] in
-            guard let self = self else { return }
-
-            if self.isPeriodicUpdatesEnabled {
-                self._updateRelays()
-            }
-        }
-
-        timerSource.schedule(wallDeadline: startTime, repeating: .seconds(kUpdateIntervalSeconds))
-        timerSource.activate()
-
-        self.timerSource = timerSource
-    }
-
-    private func makeDownloadTask(etag: String?, completionHandler: @escaping (Result<HttpResourceCacheResponse<ServerRelaysResponse>, RelayCacheError>) -> Void) -> Result<URLSessionDataTask, RestError> {
-        return rest.getRelays().dataTask(payload: ETagPayload(etag: etag, enforceWeakValidator: true, payload: EmptyPayload())) { (result) in
-            self.dispatchQueue.async {
-                completionHandler(result.mapError { RelayCacheError.rest($0) })
-            }
-        }
-    }
-
-    // MARK: - Private class methods
-
-    /// Safely read the cache file from disk using file coordinator
-    private class func read(cacheFileURL: URL) -> Result<CachedRelays, RelayCacheError> {
-        var result: Result<CachedRelays, RelayCacheError>?
-        let fileCoordinator = NSFileCoordinator(filePresenter: nil)
-
-        let accessor = { (fileURLForReading: URL) -> Void in
-            // Decode data from disk
-            result = Result { try Data(contentsOf: fileURLForReading) }
-                .mapError { RelayCacheError.readCache($0) }
-                .flatMap { (data) in
-                    Result { try JSONDecoder().decode(CachedRelays.self, from: data) }
-                        .mapError { RelayCacheError.decodeCache($0) }
-                }
-        }
-
-        var error: NSError?
-        fileCoordinator.coordinate(readingItemAt: cacheFileURL,
-                                   options: [.withoutChanges],
-                                   error: &error,
-                                   byAccessor: accessor)
-
-        if let error = error {
-            result = .failure(.readCache(error))
-        }
-
-        return result!
-    }
-
-    private class func readPrebundledRelays(fileURL: URL) -> Result<CachedRelays, RelayCacheError> {
-        return Result { try Data(contentsOf: fileURL) }
-            .mapError { RelayCacheError.readPrebundledRelays($0) }
-            .flatMap { (data) -> Result<CachedRelays, RelayCacheError> in
-                return Result { try MullvadRest.makeJSONDecoder().decode(ServerRelaysResponse.self, from: data) }
-                    .mapError { RelayCacheError.decodePrebundledRelays($0) }
-                    .map { (relays) -> CachedRelays in
-                        return CachedRelays(
-                            relays: relays,
-                            updatedAt: Date(timeIntervalSince1970: 0)
-                        )
-                }
-        }
-    }
-
-    /// Safely write the cache file on disk using file coordinator
-    private class func write(cacheFileURL: URL, record: CachedRelays) -> Result<(), RelayCacheError> {
-        var result: Result<(), RelayCacheError>?
-        let fileCoordinator = NSFileCoordinator(filePresenter: nil)
-
-        let accessor = { (fileURLForWriting: URL) -> Void in
-            result = Result { try JSONEncoder().encode(record) }
-                .mapError { RelayCacheError.encodeCache($0) }
-                .flatMap { (data) in
-                    Result { try data.write(to: fileURLForWriting) }
-                        .mapError { RelayCacheError.writeCache($0) }
-                }
-        }
-
-        var error: NSError?
-        fileCoordinator.coordinate(writingItemAt: cacheFileURL,
-                                   options: [.forReplacing],
-                                   error: &error,
-                                   byAccessor: accessor)
-
-        if let error = error {
-            result = .failure(.writeCache(error))
-        }
-
-        return result!
-    }
-
-    private class func makeWalltime(fromDate date: Date) -> DispatchWallTime {
-        let (seconds, frac) = modf(date.timeIntervalSince1970)
-
-        let nsec: Double = frac * Double(NSEC_PER_SEC)
-        let walltime = timespec(tv_sec: Int(seconds), tv_nsec: Int(nsec))
-
-        return DispatchWallTime(timespec: walltime)
-    }
-
-    private class func nextUpdateDate(lastUpdatedAt: Date) -> Date? {
-        return Calendar.current.date(
-            byAdding: .second,
-            value: kUpdateIntervalSeconds,
-            to: lastUpdatedAt
-        )
-    }
-
-    private class func shouldDownloadRelaysOnReadFailure(_ error: RelayCacheError) -> Bool {
-        switch error {
-        case .readPrebundledRelays, .decodePrebundledRelays, .decodeCache:
-            return true
-
-        case .readCache(CocoaError.fileReadNoSuchFile):
-            return true
-
-        default:
-            return false
-        }
-    }
-}
-
-/// A struct that represents the relay cache on disk
-struct CachedRelays: Codable {
-    /// E-tag returned by server
-    var etag: String?
-
-    /// The relay list stored within the cache entry
-    var relays: ServerRelaysResponse
-
-    /// The date when this cache was last updated
-    var updatedAt: Date
-}
diff --git a/ios/MullvadVPN/RelayCache/AnyRelayCacheObserver.swift b/ios/MullvadVPN/RelayCache/AnyRelayCacheObserver.swift
new file mode 100644
index 0000000000..b588530311
--- /dev/null
+++ b/ios/MullvadVPN/RelayCache/AnyRelayCacheObserver.swift
@@ -0,0 +1,31 @@
+//
+//  AnyRelayCacheObserver.swift
+//  AnyRelayCacheObserver
+//
+//  Created by pronebird on 09/09/2021.
+//  Copyright © 2021 Mullvad VPN AB. All rights reserved.
+//
+
+import Foundation
+
+extension RelayCache {
+
+    final class AnyRelayCacheObserver: WeakObserverBox, RelayCacheObserver {
+        typealias Wrapped = RelayCacheObserver
+
+        private(set) weak var inner: RelayCacheObserver?
+
+        init<T: RelayCacheObserver>(_ inner: T) {
+            self.inner = inner
+        }
+
+        func relayCache(_ relayCache: RelayCache.Tracker, didUpdateCachedRelays cachedRelays: CachedRelays) {
+            inner?.relayCache(relayCache, didUpdateCachedRelays: cachedRelays)
+        }
+
+        static func == (lhs: AnyRelayCacheObserver, rhs: AnyRelayCacheObserver) -> Bool {
+            return lhs.inner === rhs.inner
+        }
+    }
+
+}
diff --git a/ios/MullvadVPN/RelayCache/CachedRelays.swift b/ios/MullvadVPN/RelayCache/CachedRelays.swift
new file mode 100644
index 0000000000..a4cbcc93e5
--- /dev/null
+++ b/ios/MullvadVPN/RelayCache/CachedRelays.swift
@@ -0,0 +1,25 @@
+//
+//  CachedRelays.swift
+//  CachedRelays
+//
+//  Created by pronebird on 27/07/2021.
+//  Copyright © 2021 Mullvad VPN AB. All rights reserved.
+//
+
+import Foundation
+
+extension RelayCache {
+
+    /// A struct that represents the relay cache on disk
+    struct CachedRelays: Codable {
+        /// E-tag returned by server
+        var etag: String?
+
+        /// The relay list stored within the cache entry
+        var relays: REST.ServerRelaysResponse
+
+        /// The date when this cache was last updated
+        var updatedAt: Date
+    }
+
+}
diff --git a/ios/MullvadVPN/RelayCache/RelayCache.swift b/ios/MullvadVPN/RelayCache/RelayCache.swift
new file mode 100644
index 0000000000..6ad72e205a
--- /dev/null
+++ b/ios/MullvadVPN/RelayCache/RelayCache.swift
@@ -0,0 +1,11 @@
+//
+//  RelayCache.swift
+//  RelayCache
+//
+//  Created by pronebird on 06/09/2021.
+//  Copyright © 2021 Mullvad VPN AB. All rights reserved.
+//
+
+import Foundation
+
+enum RelayCache {}
diff --git a/ios/MullvadVPN/RelayCache/RelayCacheError.swift b/ios/MullvadVPN/RelayCache/RelayCacheError.swift
new file mode 100644
index 0000000000..c161ee3937
--- /dev/null
+++ b/ios/MullvadVPN/RelayCache/RelayCacheError.swift
@@ -0,0 +1,46 @@
+//
+//  RelayCacheError.swift
+//  RelayCacheError
+//
+//  Created by pronebird on 27/07/2021.
+//  Copyright © 2021 Mullvad VPN AB. All rights reserved.
+//
+
+import Foundation
+
+extension RelayCache {
+
+    /// Error emitted by RelayCache cluster.
+    enum Error: ChainedError {
+        case readCache(Swift.Error)
+        case readPrebundledRelays(Swift.Error)
+        case decodePrebundledRelays(Swift.Error)
+        case writeCache(Swift.Error)
+        case encodeCache(Swift.Error)
+        case decodeCache(Swift.Error)
+        case rest(REST.Error)
+        case backgroundTaskScheduler(Swift.Error)
+
+        var errorDescription: String? {
+            switch self {
+            case .encodeCache:
+                return "Encode cache error"
+            case .decodeCache:
+                return "Decode cache error"
+            case .readCache:
+                return "Read cache error"
+            case .readPrebundledRelays:
+                return "Read pre-bundled relays error"
+            case .decodePrebundledRelays:
+                return "Decode pre-bundled relays error"
+            case .writeCache:
+                return "Write cache error"
+            case .rest:
+                return "REST error"
+            case .backgroundTaskScheduler:
+                return "Background task scheduler error"
+            }
+        }
+    }
+
+}
diff --git a/ios/MullvadVPN/RelayCache/RelayCacheIO.swift b/ios/MullvadVPN/RelayCache/RelayCacheIO.swift
new file mode 100644
index 0000000000..fc9a13dd41
--- /dev/null
+++ b/ios/MullvadVPN/RelayCache/RelayCacheIO.swift
@@ -0,0 +1,112 @@
+//
+//  RelayCacheIO.swift
+//  RelayCacheIO
+//
+//  Created by pronebird on 27/07/2021.
+//  Copyright © 2021 Mullvad VPN AB. All rights reserved.
+//
+
+import Foundation
+
+extension RelayCache {
+    enum IO {}
+}
+
+extension RelayCache.IO {
+    /// The default cache file location bound by app group container.
+    static func defaultCacheFileURL(forSecurityApplicationGroupIdentifier appGroupIdentifier: String) -> URL? {
+        let containerURL = FileManager.default.containerURL(forSecurityApplicationGroupIdentifier: appGroupIdentifier)
+
+        return containerURL?.appendingPathComponent("relays.json")
+    }
+
+    /// The path to pre-bundled `relays.json` file.
+    static var preBundledRelaysFileURL: URL? {
+        return Bundle.main.url(forResource: "relays", withExtension: "json")
+    }
+
+    /// Safely read the cache file from disk using file coordinator.
+    static func read(cacheFileURL: URL) -> Result<RelayCache.CachedRelays, RelayCache.Error> {
+        var result: Result<RelayCache.CachedRelays, RelayCache.Error>?
+        let fileCoordinator = NSFileCoordinator(filePresenter: nil)
+
+        let accessor = { (fileURLForReading: URL) -> Void in
+            // Decode data from disk
+            result = Result { try Data(contentsOf: fileURLForReading) }
+            .mapError { RelayCache.Error.readCache($0) }
+            .flatMap { (data) in
+                Result { try JSONDecoder().decode(RelayCache.CachedRelays.self, from: data) }
+                .mapError { RelayCache.Error.decodeCache($0) }
+            }
+        }
+
+        var error: NSError?
+        fileCoordinator.coordinate(readingItemAt: cacheFileURL,
+                                   options: [.withoutChanges],
+                                   error: &error,
+                                   byAccessor: accessor)
+
+        if let error = error {
+            result = .failure(.readCache(error))
+        }
+
+        return result!
+    }
+
+    /// Safely read the cache file from disk using file coordinator and fallback to prebundled relays in case if the
+    /// relay cache file is missing.
+    static func readWithFallback(cacheFileURL: URL, preBundledRelaysFileURL: URL) -> Result<RelayCache.CachedRelays, RelayCache.Error> {
+        return Self.read(cacheFileURL: cacheFileURL)
+            .flatMapError { (error) -> Result<RelayCache.CachedRelays, RelayCache.Error> in
+                switch error {
+                case .decodeCache, .readCache(CocoaError.fileReadNoSuchFile):
+                    return RelayCache.IO.readPrebundledRelays(fileURL: preBundledRelaysFileURL)
+                default:
+                    return .failure(error)
+                }
+            }
+    }
+
+    /// Read pre-bundled relays file from disk.
+    static func readPrebundledRelays(fileURL: URL) -> Result<RelayCache.CachedRelays, RelayCache.Error> {
+        return Result { try Data(contentsOf: fileURL) }
+        .mapError { RelayCache.Error.readPrebundledRelays($0) }
+        .flatMap { (data) -> Result<RelayCache.CachedRelays, RelayCache.Error> in
+            return Result { try REST.Coding.makeJSONDecoder().decode(REST.ServerRelaysResponse.self, from: data) }
+            .mapError { RelayCache.Error.decodePrebundledRelays($0) }
+            .map { (relays) -> RelayCache.CachedRelays in
+                return RelayCache.CachedRelays(
+                    relays: relays,
+                    updatedAt: Date(timeIntervalSince1970: 0)
+                )
+            }
+        }
+    }
+
+    /// Safely write the cache file on disk using file coordinator.
+    static func write(cacheFileURL: URL, record: RelayCache.CachedRelays) -> Result<(), RelayCache.Error> {
+        var result: Result<(), RelayCache.Error>?
+        let fileCoordinator = NSFileCoordinator(filePresenter: nil)
+
+        let accessor = { (fileURLForWriting: URL) -> Void in
+            result = Result { try JSONEncoder().encode(record) }
+            .mapError { RelayCache.Error.encodeCache($0) }
+            .flatMap { (data) in
+                Result { try data.write(to: fileURLForWriting) }
+                .mapError { RelayCache.Error.writeCache($0) }
+            }
+        }
+
+        var error: NSError?
+        fileCoordinator.coordinate(writingItemAt: cacheFileURL,
+                                   options: [.forReplacing],
+                                   error: &error,
+                                   byAccessor: accessor)
+
+        if let error = error {
+            result = .failure(.writeCache(error))
+        }
+
+        return result!
+    }
+}
diff --git a/ios/MullvadVPN/RelayCache/RelayCacheObserver.swift b/ios/MullvadVPN/RelayCache/RelayCacheObserver.swift
new file mode 100644
index 0000000000..53a9edc299
--- /dev/null
+++ b/ios/MullvadVPN/RelayCache/RelayCacheObserver.swift
@@ -0,0 +1,13 @@
+//
+//  RelayCacheObserver.swift
+//  RelayCacheObserver
+//
+//  Created by pronebird on 09/09/2021.
+//  Copyright © 2021 Mullvad VPN AB. All rights reserved.
+//
+
+import Foundation
+
+protocol RelayCacheObserver: AnyObject {
+    func relayCache(_ relayCache: RelayCache.Tracker, didUpdateCachedRelays cachedRelays: RelayCache.CachedRelays)
+}
diff --git a/ios/MullvadVPN/RelayCache/RelayCacheTracker.swift b/ios/MullvadVPN/RelayCache/RelayCacheTracker.swift
new file mode 100644
index 0000000000..9e34795c88
--- /dev/null
+++ b/ios/MullvadVPN/RelayCache/RelayCacheTracker.swift
@@ -0,0 +1,246 @@
+//
+//  RelayCacheTracker.swift
+//  MullvadVPN
+//
+//  Created by pronebird on 05/06/2019.
+//  Copyright © 2019 Mullvad VPN AB. All rights reserved.
+//
+
+import Foundation
+import Logging
+
+extension RelayCache {
+
+    class Tracker {
+        /// Relay update interval (in seconds)
+        private static let relayUpdateInterval: TimeInterval = 60 * 60
+
+        /// Tracker log
+        private let logger = Logger(label: "RelayCacheTracker")
+
+        /// The cache location used by the class instance
+        private let cacheFileURL: URL
+
+        /// The location of prebundled `relays.json`
+        private let prebundledRelaysFileURL: URL
+
+        /// A dispatch queue used for thread synchronization
+        private let stateQueue = DispatchQueue(label: "RelayCacheTrackerStateQueue")
+
+        /// A dispatch queue used for serializing relay cache updates
+        private let updateQueue = DispatchQueue(label: "RelayCacheTrackerUpdateQueue")
+
+        /// A timer source used for periodic updates
+        private var timerSource: DispatchSourceTimer?
+
+        /// A flag that indicates whether periodic updates are running
+        private var isPeriodicUpdatesEnabled = false
+
+        /// Observers
+        private let observerList = ObserverList<AnyRelayCacheObserver>()
+
+        /// A shared instance of `RelayCache`
+        static let shared: RelayCache.Tracker = {
+            let cacheFileURL = RelayCache.IO.defaultCacheFileURL(forSecurityApplicationGroupIdentifier: ApplicationConfiguration.securityGroupIdentifier)!
+            let prebundledRelaysFileURL = RelayCache.IO.preBundledRelaysFileURL!
+
+            return Tracker(
+                cacheFileURL: cacheFileURL,
+                prebundledRelaysFileURL: prebundledRelaysFileURL
+            )
+        }()
+
+        private init(cacheFileURL: URL, prebundledRelaysFileURL: URL) {
+            self.cacheFileURL = cacheFileURL
+            self.prebundledRelaysFileURL = prebundledRelaysFileURL
+        }
+
+        func startPeriodicUpdates() {
+            stateQueue.async {
+                guard !self.isPeriodicUpdatesEnabled else { return }
+
+                self.logger.debug("Start periodic relay updates")
+
+                self.isPeriodicUpdatesEnabled = true
+
+                switch RelayCache.IO.read(cacheFileURL: self.cacheFileURL) {
+                case .success(let cachedRelays):
+                    let nextUpdate = cachedRelays.updatedAt.addingTimeInterval(Self.relayUpdateInterval)
+                    self.scheduleRepeatingTimer(startTime: .now() + nextUpdate.timeIntervalSinceNow)
+
+                case .failure(let readError):
+                    self.logger.error(chainedError: readError, message: "Failed to read the relay cache")
+
+                    if Self.shouldDownloadRelaysOnReadFailure(readError) {
+                        self.scheduleRepeatingTimer(startTime: .now())
+                    }
+                }
+            }
+        }
+
+        func stopPeriodicUpdates() {
+            stateQueue.async {
+                guard self.isPeriodicUpdatesEnabled else { return }
+
+                self.logger.debug("Stop periodic relay updates")
+
+                self.isPeriodicUpdatesEnabled = false
+
+                self.timerSource?.cancel()
+                self.timerSource = nil
+            }
+        }
+
+        func updateRelays() -> Result<RelayCache.FetchResult, RelayCache.Error>.Promise {
+            return Promise.deferred {
+                return RelayCache.IO.read(cacheFileURL: self.cacheFileURL)
+            }
+            .schedule(on: stateQueue)
+            .then { result in
+                switch result {
+                case .success(let cachedRelays):
+                    let nextUpdate = cachedRelays.updatedAt.addingTimeInterval(Self.relayUpdateInterval)
+
+                    if nextUpdate <= Date() {
+                        return self.downloadRelays(previouslyCachedRelays: cachedRelays)
+                    } else {
+                        return .success(.throttled)
+                    }
+
+                case .failure(let readError):
+                    self.logger.error(chainedError: readError, message: "Failed to read the relay cache to determine if it needs to be updated")
+
+                    if Self.shouldDownloadRelaysOnReadFailure(readError) {
+                        return self.downloadRelays(previouslyCachedRelays: nil)
+                    } else {
+                        return .failure(readError)
+                    }
+                }
+            }
+            .block(on: updateQueue)
+        }
+
+        func read() -> Result<CachedRelays, RelayCache.Error>.Promise {
+            return Promise.deferred {
+                return RelayCache.IO.readWithFallback(
+                    cacheFileURL: self.cacheFileURL,
+                    preBundledRelaysFileURL: self.prebundledRelaysFileURL
+                )
+            }.schedule(on: stateQueue)
+        }
+
+        // MARK: - Observation
+
+        func addObserver<T: RelayCacheObserver>(_ observer: T) {
+            observerList.append(AnyRelayCacheObserver(observer))
+        }
+
+        func removeObserver<T: RelayCacheObserver>(_ observer: T) {
+            observerList.remove(AnyRelayCacheObserver(observer))
+        }
+
+        // MARK: - Private instance methods
+
+        private func downloadRelays(previouslyCachedRelays: CachedRelays?) -> Result<RelayCache.FetchResult, RelayCache.Error>.Promise {
+            return REST.Client.shared.getRelays(etag: previouslyCachedRelays?.etag)
+                .receive(on: stateQueue)
+                .mapError { error in
+                    self.logger.error(chainedError: error, message: "Failed to download relays")
+                    return RelayCache.Error.rest(error)
+                }
+                .mapThen { result in
+                    switch result {
+                    case .newContent(let etag, let relays):
+                        let numRelays = relays.wireguard.relays.count
+
+                        self.logger.info("Downloaded \(numRelays) relays")
+
+                        let cachedRelays = CachedRelays(etag: etag, relays: relays, updatedAt: Date())
+
+                        return RelayCache.IO.write(cacheFileURL: self.cacheFileURL, record: cachedRelays)
+                            .asPromise()
+                            .map { _ in
+                                self.observerList.forEach { (observer) in
+                                    observer.relayCache(self, didUpdateCachedRelays: cachedRelays)
+                                }
+
+                                return .newContent
+                            }
+                            .onFailure { error in
+                                self.logger.error(chainedError: error, message: "Failed to store downloaded relays")
+                            }
+
+                    case .notModified:
+                        self.logger.info("Relays haven't changed since last check.")
+
+                        var cachedRelays = previouslyCachedRelays!
+                        cachedRelays.updatedAt = Date()
+
+                        return RelayCache.IO.write(cacheFileURL: self.cacheFileURL, record: cachedRelays)
+                            .asPromise()
+                            .map { _ in
+                                return .sameContent
+                            }
+                            .onFailure { error in
+                                self.logger.error(chainedError: error, message: "Failed to update cached relays timestamp")
+                            }
+                    }
+                }
+        }
+
+        private func scheduleRepeatingTimer(startTime: DispatchWallTime) {
+            let timerSource = DispatchSource.makeTimerSource(queue: stateQueue)
+            timerSource.setEventHandler { [weak self] in
+                self?.updateRelays().observe { _ in }
+            }
+
+            timerSource.schedule(wallDeadline: startTime, repeating: .seconds(Int(Self.relayUpdateInterval)))
+            timerSource.activate()
+
+            self.timerSource = timerSource
+        }
+
+        // MARK: - Private class methods
+
+        private class func shouldDownloadRelaysOnReadFailure(_ error: RelayCache.Error) -> Bool {
+            switch error {
+            case .readPrebundledRelays, .decodePrebundledRelays, .decodeCache:
+                return true
+
+            case .readCache(CocoaError.fileReadNoSuchFile):
+                return true
+
+            default:
+                return false
+            }
+        }
+    }
+
+}
+
+extension RelayCache {
+
+    /// Type describing the result of an attempt to fetch the new relay list from server.
+    enum FetchResult: CustomStringConvertible {
+        /// Request to update relays was throttled.
+        case throttled
+
+        /// Refreshed relays but the same content was found on remote.
+        case sameContent
+
+        /// Refreshed relays with new content.
+        case newContent
+
+        var description: String {
+            switch self {
+            case .throttled:
+                return "throttled"
+            case .sameContent:
+                return "same content"
+            case .newContent:
+                return "new content"
+            }
+        }
+    }
+
+}
diff --git a/ios/MullvadVPN/SelectLocationViewController.swift b/ios/MullvadVPN/SelectLocationViewController.swift
index 222aa14b85..3b672c2c09 100644
--- a/ios/MullvadVPN/SelectLocationViewController.swift
+++ b/ios/MullvadVPN/SelectLocationViewController.swift
@@ -25,7 +25,7 @@ class SelectLocationViewController: UIViewController, UITableViewDelegate {
 
     private let logger = Logger(label: "SelectLocationController")
     private var dataSource: LocationDataSource?
-    private var setCachedRelaysOnViewDidLoad: CachedRelays?
+    private var setCachedRelaysOnViewDidLoad: RelayCache.CachedRelays?
     private var setRelayLocationOnViewDidLoad: RelayLocation?
     private var setScrollPositionOnViewDidLoad: UITableView.ScrollPosition = .none
     private var isViewAppeared = false
@@ -203,7 +203,7 @@ class SelectLocationViewController: UIViewController, UITableViewDelegate {
 
     // MARK: - Public
 
-    func setCachedRelays(_ cachedRelays: CachedRelays) {
+    func setCachedRelays(_ cachedRelays: RelayCache.CachedRelays) {
         guard isViewLoaded else {
             self.setCachedRelaysOnViewDidLoad = cachedRelays
             return