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// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// microproxy proxies incoming HTTPS connections to another
// destination. Instead of managing its own TLS certificates, it
// borrows issued certificates and keys from an autocert directory.
package main
import (
"crypto/tls"
"encoding/json"
"flag"
"fmt"
"io"
"io/ioutil"
"log"
"net/http"
"net/http/httputil"
"net/url"
"path/filepath"
"strings"
"sync"
"time"
"tailscale.com/logpolicy"
"tailscale.com/tsweb"
)
var (
addr = flag.String("addr", ":4430", "server address")
certdir = flag.String("certdir", "", "directory to borrow LetsEncrypt certificates from")
hostname = flag.String("hostname", "", "hostname to serve")
logCollection = flag.String("logcollection", "", "If non-empty, logtail collection to log to")
nodeExporter = flag.String("node-exporter", "http://localhost:9100", "URL of the local prometheus node exporter")
goVarsURL = flag.String("go-vars-url", "http://localhost:8383/debug/vars", "URL of a local Go server's /debug/vars endpoint")
insecure = flag.Bool("insecure", false, "serve over http, for development")
)
func main() {
flag.Parse()
if *logCollection != "" {
logpolicy.New(*logCollection)
}
ne, err := url.Parse(*nodeExporter)
if err != nil {
log.Fatalf("Couldn't parse URL %q: %v", *nodeExporter, err)
}
proxy := httputil.NewSingleHostReverseProxy(ne)
proxy.FlushInterval = time.Second
if _, err = url.Parse(*goVarsURL); err != nil {
log.Fatalf("Couldn't parse URL %q: %v", *goVarsURL, err)
}
mux := http.NewServeMux()
tsweb.Debugger(mux) // registers /debug/*
mux.Handle("/metrics", tsweb.Protected(proxy))
mux.Handle("/varz", tsweb.Protected(tsweb.StdHandler(&goVarsHandler{*goVarsURL}, tsweb.HandlerOptions{
Quiet200s: true,
Logf: log.Printf,
})))
ch := &certHolder{
hostname: *hostname,
path: filepath.Join(*certdir, *hostname),
}
httpsrv := &http.Server{
Addr: *addr,
Handler: mux,
}
if !*insecure {
httpsrv.TLSConfig = &tls.Config{GetCertificate: ch.GetCertificate}
err = httpsrv.ListenAndServeTLS("", "")
} else {
err = httpsrv.ListenAndServe()
}
if err != nil && err != http.ErrServerClosed {
log.Fatal(err)
}
}
type goVarsHandler struct {
url string
}
func promPrint(w io.Writer, prefix string, obj map[string]interface{}) {
for k, i := range obj {
if prefix != "" {
k = prefix + "_" + k
}
switch v := i.(type) {
case map[string]interface{}:
promPrint(w, k, v)
case float64:
const saveConfigReject = "control_save_config_rejected_"
const saveConfig = "control_save_config_"
switch {
case strings.HasPrefix(k, saveConfigReject):
fmt.Fprintf(w, "control_save_config_rejected{reason=%q} %f\n", k[len(saveConfigReject):], v)
case strings.HasPrefix(k, saveConfig):
fmt.Fprintf(w, "control_save_config{reason=%q} %f\n", k[len(saveConfig):], v)
default:
fmt.Fprintf(w, "%s %f\n", k, v)
}
default:
fmt.Fprintf(w, "# Skipping key %q, unhandled type %T\n", k, v)
}
}
}
func (h *goVarsHandler) ServeHTTPReturn(w http.ResponseWriter, r *http.Request) error {
resp, err := http.Get(h.url)
if err != nil {
return tsweb.Error(http.StatusInternalServerError, "fetch failed", err)
}
defer resp.Body.Close()
var mon map[string]interface{}
if err := json.NewDecoder(resp.Body).Decode(&mon); err != nil {
return tsweb.Error(http.StatusInternalServerError, "fetch failed", err)
}
w.WriteHeader(http.StatusOK)
promPrint(w, "", mon)
return nil
}
// certHolder loads and caches a TLS certificate from disk, reloading
// it every hour.
type certHolder struct {
hostname string // only hostname allowed in SNI
path string // path of certificate+key combined PEM file
mu sync.Mutex
cert *tls.Certificate // cached parsed cert+key
loaded time.Time
}
func (c *certHolder) GetCertificate(ch *tls.ClientHelloInfo) (*tls.Certificate, error) {
if ch.ServerName != c.hostname {
return nil, fmt.Errorf("wrong client SNI %q", ch.ServerName)
}
c.mu.Lock()
defer c.mu.Unlock()
if time.Since(c.loaded) > time.Hour {
if err := c.loadLocked(); err != nil {
log.Printf("Reloading cert %q: %v", c.path, err)
// continue anyway, we might be able to serve off the stale cert.
}
}
return c.cert, nil
}
// load reloads the TLS certificate and key from disk. Caller must
// hold mu.
func (c *certHolder) loadLocked() error {
bs, err := ioutil.ReadFile(c.path)
if err != nil {
return fmt.Errorf("reading %q: %v", c.path, err)
}
cert, err := tls.X509KeyPair(bs, bs)
if err != nil {
return fmt.Errorf("parsing %q: %v", c.path, err)
}
c.cert = &cert
c.loaded = time.Now()
return nil
}
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