Before that change, etcd and zookeeper would fail to instantiate

the discovery without the key being already there in the store or
created beforehand and implicitely by a 'swarm join'.

Signed-off-by: Alexandre Beslic <abronan@docker.com>
Signed-off-by: Victor Vieux <vieux@docker.com>

This PR allows to configure the discovery path using the
--discovery-opt flag (with "kv.path=path/to/nodes"). We
can point to "docker/nodes" and use the docker discovery.

If docker instances are advertising to the cluster using
the `--cluster-advertise` flag, the swarm join command
becomes unnecessary.

Signed-off-by: Alexandre Beslic <abronan@docker.com>
Signed-off-by: Victor Vieux <vieux@docker.com>

docs/reference/commandline/daemon.md

@@ -603,6 +603,10 @@ The currently supported cluster store options are:
     private key is used as the client key for communication with the
     Key/Value store.
 
+*  `kv.path`
+
+    Specifies the path in the Key/Value store. If not configured, the default value is 'docker/nodes'.
+
 ## Access authorization
 
 Docker's access authorization can be extended by authorization plugins that your

pkg/discovery/kv/kv.go

@@ -17,7 +17,7 @@ import (
 )
 
 const (
-	discoveryPath = "docker/nodes"
+	defaultDiscoveryPath = "docker/nodes"
 )
 
 // Discovery is exported
@@ -62,7 +62,14 @@ func (s *Discovery) Initialize(uris string, heartbeat time.Duration, ttl time.Du
 
 	s.heartbeat = heartbeat
 	s.ttl = ttl
-	s.path = path.Join(s.prefix, discoveryPath)
+
+	// Use a custom path if specified in discovery options
+	dpath := defaultDiscoveryPath
+	if clusterOpts["kv.path"] != "" {
+		dpath = clusterOpts["kv.path"]
+	}
+
+	s.path = path.Join(s.prefix, dpath)
 
 	var config *store.Config
 	if clusterOpts["kv.cacertfile"] != "" && clusterOpts["kv.certfile"] != "" && clusterOpts["kv.keyfile"] != "" {
@@ -138,6 +145,17 @@ func (s *Discovery) Watch(stopCh <-chan struct{}) (<-chan discovery.Entries, <-c
 		// Forever: Create a store watch, watch until we get an error and then try again.
 		// Will only stop if we receive a stopCh request.
 		for {
+			// Create the path to watch if it does not exist yet
+			exists, err := s.store.Exists(s.path)
+			if err != nil {
+				errCh <- err
+			}
+			if !exists {
+				if err := s.store.Put(s.path, []byte(""), &store.WriteOptions{IsDir: true}); err != nil {
+					errCh <- err
+				}
+			}
+
 			// Set up a watch.
 			watchCh, err := s.store.WatchTree(s.path, stopCh)
 			if err != nil {

pkg/discovery/kv/kv_test.go

@@ -33,7 +33,7 @@ func (ds *DiscoverySuite) TestInitialize(c *check.C) {
 	s := d.store.(*FakeStore)
 	c.Assert(s.Endpoints, check.HasLen, 1)
 	c.Assert(s.Endpoints[0], check.Equals, "127.0.0.1")
-	c.Assert(d.path, check.Equals, discoveryPath)
+	c.Assert(d.path, check.Equals, defaultDiscoveryPath)
 
 	storeMock = &FakeStore{
 		Endpoints: []string{"127.0.0.1:1234"},
@@ -45,7 +45,7 @@ func (ds *DiscoverySuite) TestInitialize(c *check.C) {
 	s = d.store.(*FakeStore)
 	c.Assert(s.Endpoints, check.HasLen, 1)
 	c.Assert(s.Endpoints[0], check.Equals, "127.0.0.1:1234")
-	c.Assert(d.path, check.Equals, "path/"+discoveryPath)
+	c.Assert(d.path, check.Equals, "path/"+defaultDiscoveryPath)
 
 	storeMock = &FakeStore{
 		Endpoints: []string{"127.0.0.1:1234", "127.0.0.2:1234", "127.0.0.3:1234"},
@@ -60,7 +60,7 @@ func (ds *DiscoverySuite) TestInitialize(c *check.C) {
 	c.Assert(s.Endpoints[1], check.Equals, "127.0.0.2:1234")
 	c.Assert(s.Endpoints[2], check.Equals, "127.0.0.3:1234")
 
-	c.Assert(d.path, check.Equals, "path/"+discoveryPath)
+	c.Assert(d.path, check.Equals, "path/"+defaultDiscoveryPath)
 }
 
 // Extremely limited mock store so we can test initialization
@@ -224,8 +224,8 @@ func (ds *DiscoverySuite) TestWatch(c *check.C) {
 		&discovery.Entry{Host: "2.2.2.2", Port: "2222"},
 	}
 	kvs := []*store.KVPair{
-		{Key: path.Join("path", discoveryPath, "1.1.1.1"), Value: []byte("1.1.1.1:1111")},
-		{Key: path.Join("path", discoveryPath, "2.2.2.2"), Value: []byte("2.2.2.2:2222")},
+		{Key: path.Join("path", defaultDiscoveryPath, "1.1.1.1"), Value: []byte("1.1.1.1:1111")},
+		{Key: path.Join("path", defaultDiscoveryPath, "2.2.2.2"), Value: []byte("2.2.2.2:2222")},
 	}
 
 	stopCh := make(chan struct{})
@@ -245,7 +245,7 @@ func (ds *DiscoverySuite) TestWatch(c *check.C) {
 
 	// Add a new entry.
 	expected = append(expected, &discovery.Entry{Host: "3.3.3.3", Port: "3333"})
-	kvs = append(kvs, &store.KVPair{Key: path.Join("path", discoveryPath, "3.3.3.3"), Value: []byte("3.3.3.3:3333")})
+	kvs = append(kvs, &store.KVPair{Key: path.Join("path", defaultDiscoveryPath, "3.3.3.3"), Value: []byte("3.3.3.3:3333")})
 	mockCh <- kvs
 	c.Assert(<-ch, check.DeepEquals, expected)