Support TLS connections to remote daemons

container/client.go

@@ -1,6 +1,7 @@
 package container
 
 import (
+	"crypto/tls"
 	"time"
 
 	log "github.com/Sirupsen/logrus"
@@ -21,8 +22,8 @@ type Client interface {
 	IsContainerStale(Container) (bool, error)
 }
 
-func NewClient(dockerHost string, pullImages bool) Client {
-	docker, err := dockerclient.NewDockerClient(dockerHost, nil)
+func NewClient(dockerHost string, tlsConfig *tls.Config, pullImages bool) Client {
+	docker, err := dockerclient.NewDockerClient(dockerHost, tlsConfig)
 
 	if err != nil {
 		log.Fatalf("Error instantiating Docker client: %s", err)

main.go

@@ -1,9 +1,13 @@
 package main // import "github.com/CenturyLinkLabs/watchtower"
 
 import (
+	"crypto/tls"
+	"crypto/x509"
 	"fmt"
+	"io/ioutil"
 	"os"
 	"os/signal"
+	"strings"
 	"sync"
 	"syscall"
 	"time"
@@ -15,10 +19,22 @@ import (
 )
 
 var (
-	wg sync.WaitGroup
+	wg           sync.WaitGroup
+	client       container.Client
+	pollInterval time.Duration
 )
 
+func init() {
+	log.SetLevel(log.InfoLevel)
+}
+
 func main() {
+	rootCertPath := "/etc/ssl/docker"
+
+	if os.Getenv("DOCKER_CERT_PATH") != "" {
+		rootCertPath = os.Getenv("DOCKER_CERT_PATH")
+	}
+
 	app := cli.NewApp()
 	app.Name = "watchtower"
 	app.Usage = "Automatically update running Docker containers"
@@ -27,27 +43,87 @@ func main() {
 	app.Flags = []cli.Flag{
 		cli.StringFlag{
 			Name:   "host, H",
+			Usage:  "daemon socket to connect to",
 			Value:  "unix:///var/run/docker.sock",
-			Usage:  "Docker daemon socket to connect to",
 			EnvVar: "DOCKER_HOST",
 		},
 		cli.IntFlag{
 			Name:  "interval, i",
-			Value: 300,
 			Usage: "poll interval (in seconds)",
+			Value: 300,
 		},
 		cli.BoolFlag{
 			Name:  "no-pull",
 			Usage: "do not pull new images",
 		},
+		cli.BoolFlag{
+			Name:  "tls",
+			Usage: "use TLS; implied by --tlsverify",
+		},
+		cli.BoolFlag{
+			Name:   "tlsverify",
+			Usage:  "use TLS and verify the remote",
+			EnvVar: "DOCKER_TLS_VERIFY",
+		},
+		cli.StringFlag{
+			Name:  "tlscacert",
+			Usage: "trust certs signed only by this CA",
+			Value: fmt.Sprintf("%s/ca.pem", rootCertPath),
+		},
+		cli.StringFlag{
+			Name:  "tlscert",
+			Usage: "client certificate for TLS authentication",
+			Value: fmt.Sprintf("%s/cert.pem", rootCertPath),
+		},
+		cli.StringFlag{
+			Name:  "tlskey",
+			Usage: "client key for TLS authentication",
+			Value: fmt.Sprintf("%s/key.pem", rootCertPath),
+		},
 		cli.BoolFlag{
 			Name:  "debug",
 			Usage: "enable debug mode with verbose logging",
 		},
 	}
 
+	if err := app.Run(os.Args); err != nil {
+		log.Fatal(err)
+	}
+}
+
+func before(c *cli.Context) error {
+	if c.GlobalBool("debug") {
+		log.SetLevel(log.DebugLevel)
+	}
+
+	pollInterval = time.Duration(c.Int("interval")) * time.Second
+
+	// Set-up container client
+	tls, err := tlsConfig(c)
+	if err != nil {
+		return err
+	}
+
+	client = container.NewClient(c.GlobalString("host"), tls, !c.GlobalBool("no-pull"))
+
 	handleSignals()
-	app.Run(os.Args)
+	return nil
+}
+
+func start(*cli.Context) {
+	if err := actions.CheckPrereqs(client); err != nil {
+		log.Fatal(err)
+	}
+
+	for {
+		wg.Add(1)
+		if err := actions.Update(client); err != nil {
+			fmt.Println(err)
+		}
+		wg.Done()
+
+		time.Sleep(pollInterval)
+	}
 }
 
 func handleSignals() {
@@ -63,34 +139,56 @@ func handleSignals() {
 	}()
 }
 
-func before(c *cli.Context) error {
-	if c.GlobalBool("debug") {
-		log.SetLevel(log.DebugLevel)
-	} else {
-		log.SetLevel(log.InfoLevel)
-	}
+// tlsConfig translates the command-line options into a tls.Config struct
+func tlsConfig(c *cli.Context) (*tls.Config, error) {
+	var tlsConfig *tls.Config
+	var err error
+	caCertFlag := c.GlobalString("tlscacert")
+	certFlag := c.GlobalString("tlscert")
+	keyFlag := c.GlobalString("tlskey")
 
-	client := newContainerClient(c)
-	return actions.CheckPrereqs(client)
-}
+	if c.GlobalBool("tls") || c.GlobalBool("tlsverify") {
+		tlsConfig = &tls.Config{
+			InsecureSkipVerify: !c.GlobalBool("tlsverify"),
+		}
 
-func start(c *cli.Context) {
-	client := newContainerClient(c)
-	secs := time.Duration(c.Int("interval")) * time.Second
+		// Load CA cert
+		if caCertFlag != "" {
+			var caCert []byte
 
-	for {
-		wg.Add(1)
-		if err := actions.Update(client); err != nil {
-			fmt.Println(err)
+			if strings.HasPrefix(caCertFlag, "/") {
+				caCert, err = ioutil.ReadFile(caCertFlag)
+				if err != nil {
+					return nil, err
+				}
+			} else {
+				caCert = []byte(caCertFlag)
+			}
+
+			caCertPool := x509.NewCertPool()
+			caCertPool.AppendCertsFromPEM(caCert)
+
+			tlsConfig.RootCAs = caCertPool
 		}
-		wg.Done()
 
-		time.Sleep(secs)
+		// Load client certificate
+		if certFlag != "" && keyFlag != "" {
+			var cert tls.Certificate
+
+			if strings.HasPrefix(certFlag, "/") && strings.HasPrefix(keyFlag, "/") {
+				cert, err = tls.LoadX509KeyPair(certFlag, keyFlag)
+				if err != nil {
+					return nil, err
+				}
+			} else {
+				cert, err = tls.X509KeyPair([]byte(certFlag), []byte(keyFlag))
+				if err != nil {
+					return nil, err
+				}
+			}
+			tlsConfig.Certificates = []tls.Certificate{cert}
+		}
 	}
-}
 
-func newContainerClient(c *cli.Context) container.Client {
-	dockerHost := c.GlobalString("host")
-	noPull := c.GlobalBool("no-pull")
-	return container.NewClient(dockerHost, !noPull)
+	return tlsConfig, nil
 }