leader election: Display replica status in docker info.

Signed-off-by: Andrea Luzzardi <aluzzardi@gmail.com>

api/handlers.go

@@ -27,7 +27,7 @@ func getInfo(c *context, w http.ResponseWriter, r *http.Request) {
 	info := dockerclient.Info{
 		Containers:      int64(len(c.cluster.Containers())),
 		Images:          int64(len(c.cluster.Images())),
-		DriverStatus:    c.cluster.Info(),
+		DriverStatus:    c.statusHandler.Status(),
 		NEventsListener: int64(c.eventsHandler.Size()),
 		Debug:           c.debug,
 		MemoryLimit:     true,

api/proxy.go

@@ -2,18 +2,24 @@ package api
 
 import (
 	"crypto/tls"
+	"fmt"
 	"net/http"
+	"strings"
 )
 
+var localRoutes = []string{"/info", "/_ping"}
+
 // ReverseProxy is a Docker reverse proxy.
 type ReverseProxy struct {
+	api       http.Handler
 	tlsConfig *tls.Config
 	dest      string
 }
 
 // NewReverseProxy creates a new reverse proxy.
-func NewReverseProxy(tlsConfig *tls.Config) *ReverseProxy {
+func NewReverseProxy(api http.Handler, tlsConfig *tls.Config) *ReverseProxy {
 	return &ReverseProxy{
+		api:       api,
 		tlsConfig: tlsConfig,
 	}
 }
@@ -26,12 +32,21 @@ func (p *ReverseProxy) SetDestination(dest string) {
 
 // ServeHTTP is the http.Handler.
 func (p *ReverseProxy) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	// Check whether we should handle this request locally.
+	for _, route := range localRoutes {
+		if strings.HasSuffix(r.URL.Path, route) {
+			p.api.ServeHTTP(w, r)
+			return
+		}
+	}
+
+	// Otherwise, forward.
 	if p.dest == "" {
 		httpError(w, "No cluster leader", http.StatusInternalServerError)
 		return
 	}
 
 	if err := hijack(p.tlsConfig, p.dest, w, r); err != nil {
-		httpError(w, err.Error(), http.StatusInternalServerError)
+		httpError(w, fmt.Sprintf("Unable to reach cluster leader: %v", err), http.StatusInternalServerError)
 	}
 }

api/router.go

@@ -13,6 +13,7 @@ import (
 type context struct {
 	cluster       cluster.Cluster
 	eventsHandler *eventsHandler
+	statusHandler StatusHandler
 	debug         bool
 	tlsConfig     *tls.Config
 }
@@ -83,7 +84,7 @@ func writeCorsHeaders(w http.ResponseWriter, r *http.Request) {
 }
 
 // NewRouter creates a new API router.
-func NewRouter(cluster cluster.Cluster, tlsConfig *tls.Config, enableCors bool) *mux.Router {
+func NewRouter(cluster cluster.Cluster, tlsConfig *tls.Config, status StatusHandler, enableCors bool) *mux.Router {
 	// Register the API events handler in the cluster.
 	eventsHandler := newEventsHandler()
 	cluster.RegisterEventHandler(eventsHandler)
@@ -91,6 +92,7 @@ func NewRouter(cluster cluster.Cluster, tlsConfig *tls.Config, enableCors bool)
 	context := &context{
 		cluster:       cluster,
 		eventsHandler: eventsHandler,
+		statusHandler: status,
 		tlsConfig:     tlsConfig,
 	}
 

api/status.go

@@ -0,0 +1,7 @@
+package api
+
+// StatusHandler allows the API to display extra information on docker info.
+type StatusHandler interface {
+	// Info provides key/values to be added to docker info.
+	Status() [][]string
+}

cli/flags.go

@@ -119,7 +119,7 @@ var (
 	}
 
 	flLeaderElection = cli.BoolFlag{
-		Name:  "leader-election",
-		Usage: "Enable cluster leader election between Swarm managers",
+		Name:  "replication",
+		Usage: "Enable Swarm manager replication",
 	}
 )

cli/manage.go

@@ -5,7 +5,6 @@ import (
 	"crypto/x509"
 	"fmt"
 	"io/ioutil"
-	"net/http"
 	"path"
 	"time"
 
@@ -41,6 +40,30 @@ func (h *logHandler) Handle(e *cluster.Event) error {
 	return nil
 }
 
+type statusHandler struct {
+	cluster   cluster.Cluster
+	candidate *leadership.Candidate
+	follower  *leadership.Follower
+}
+
+func (h *statusHandler) Status() [][]string {
+	var status [][]string
+
+	if h.candidate != nil && !h.candidate.IsLeader() {
+		status = [][]string{
+			{"\bRole", "replica"},
+			{"\bPrimary", h.follower.Leader()},
+		}
+	} else {
+		status = [][]string{
+			{"\bRole", "primary"},
+		}
+	}
+
+	status = append(status, h.cluster.Info()...)
+	return status
+}
+
 // Load the TLS certificates/keys and, if verify is true, the CA.
 func loadTLSConfig(ca, cert, key string, verify bool) (*tls.Config, error) {
 	c, err := tls.LoadX509KeyPair(cert, key)
@@ -91,7 +114,7 @@ func createDiscovery(uri string, c *cli.Context) discovery.Discovery {
 	return discovery
 }
 
-func setupLeaderElection(server *api.Server, apiHandler http.Handler, discovery discovery.Discovery, addr string, tlsConfig *tls.Config) {
+func setupReplication(c *cli.Context, cluster cluster.Cluster, server *api.Server, discovery discovery.Discovery, addr string, tlsConfig *tls.Config) {
 	kvDiscovery, ok := discovery.(*kvdiscovery.Discovery)
 	if !ok {
 		log.Fatal("Leader election is only supported with consul, etcd and zookeeper discovery.")
@@ -101,7 +124,8 @@ func setupLeaderElection(server *api.Server, apiHandler http.Handler, discovery
 	candidate := leadership.NewCandidate(client, leaderElectionPath, addr)
 	follower := leadership.NewFollower(client, leaderElectionPath)
 
-	proxy := api.NewReverseProxy(tlsConfig)
+	router := api.NewRouter(cluster, tlsConfig, &statusHandler{cluster, candidate, follower}, c.Bool("cors"))
+	proxy := api.NewReverseProxy(router, tlsConfig)
 
 	go func() {
 		candidate.RunForElection()
@@ -109,7 +133,7 @@ func setupLeaderElection(server *api.Server, apiHandler http.Handler, discovery
 		for isElected := range electedCh {
 			if isElected {
 				log.Info("Cluster leadership acquired")
-				server.SetHandler(apiHandler)
+				server.SetHandler(router)
 			} else {
 				log.Info("Cluster leadership lost")
 				server.SetHandler(proxy)
@@ -129,6 +153,8 @@ func setupLeaderElection(server *api.Server, apiHandler http.Handler, discovery
 			}
 		}
 	}()
+
+	server.SetHandler(router)
 }
 
 func manage(c *cli.Context) {
@@ -208,9 +234,7 @@ func manage(c *cli.Context) {
 	}
 
 	server := api.NewServer(hosts, tlsConfig)
-	router := api.NewRouter(cl, tlsConfig, c.Bool("cors"))
-
-	if c.Bool("leader-election") {
+	if c.Bool("replication") {
 		addr := c.String("advertise")
 		if addr == "" {
 			log.Fatal("--advertise address must be provided when using --leader-election")
@@ -219,9 +243,9 @@ func manage(c *cli.Context) {
 			log.Fatal("--advertise should be of the form ip:port or hostname:port")
 		}
 
-		setupLeaderElection(server, router, discovery, addr, tlsConfig)
+		setupReplication(c, cl, server, discovery, addr, tlsConfig)
 	} else {
-		server.SetHandler(router)
+		server.SetHandler(api.NewRouter(cl, tlsConfig, &statusHandler{cl, nil, nil}, c.Bool("cors")))
 	}
 
 	log.Fatal(server.ListenAndServe())