Add peer discovery for Docker Swarm

The peer discovery relies on "GET /info" API call which returns
list of master nodes. The peer list is passed to weaver when
launching it.

If node is a master, then we pass "--ipalloc-alloc
consensus=$(MASTER_NODES_COUNT)" to weaver. Otherwise, we pass
"--ipalloc-alloc observer".

prog/v2-plugin/config.json

@@ -21,6 +21,18 @@
       "destination": "/procmount",
       "type": "proc",
       "source": "proc"
+    },
+    {
+      "destination": "/var/run/docker.sock",
+      "source": "/var/run/docker.sock",
+      "type": "bind",
+      "options": ["rbind"]
+    },
+    {
+      "destination": "/var/lib/weave",
+      "source": "/var/lib/weave",
+      "type": "bind",
+      "options": ["rbind"]
     }
   ],
   "network": {

prog/v2-plugin/launch.sh

@@ -7,13 +7,16 @@ IPALLOC_RANGE=${IPALLOC_RANGE:-10.32.0.0/12}
 HTTP_ADDR=${WEAVE_HTTP_ADDR:-127.0.0.1:6784}
 STATUS_ADDR=${WEAVE_STATUS_ADDR:-0.0.0.0:6782}
 HOST_ROOT=${HOST_ROOT:-/host}
-LOG_FILE=/tmp/weaver.log
+LOG_FILE=/var/lib/weave/weaver.log
 
 echo "Starting launch.sh" >>$LOG_FILE
 
 # Check if the IP range overlaps anything existing on the host
 /usr/bin/weaveutil netcheck $IPALLOC_RANGE weave
 
+SWARM_PEERS=$(/usr/bin/weaveutil swarm-manager-peers 2>>$LOG_FILE)
+! /usr/bin/weaveutil is-swarm-manager 2>>$LOG_FILE || IS_SWARM_MANAGER=1
+
 /home/weave/weave --local create-bridge --force >>$LOG_FILE 2>&1
 
 BRIDGE_OPTIONS="--datapath=datapath"
@@ -29,8 +32,11 @@ if [ "$(/home/weave/weave --local bridge-type)" = "bridge" ]; then
 fi
 
 if [ -z "$IPALLOC_INIT" ]; then
-    # ideally we would know the peer count
-    IPALLOC_INIT="consensus"
+    if [ $IS_SWARM_MANAGER == "1" ]; then
+        IPALLOC_INIT="consensus=$(echo $SWARM_PEERS | wc -l)"
+    else
+        IPALLOC_INIT="observer"
+    fi
 fi
 
 /home/weave/weaver $EXTRA_ARGS --port=6783 $BRIDGE_OPTIONS \
@@ -38,6 +44,7 @@ fi
     --ipalloc-range=$IPALLOC_RANGE \
     --ipalloc-init $IPALLOC_INIT \
     --nickname "$(hostname)" \
+    $(echo $SWARM_PEERS | tr '\n' ' ') \
     >>$LOG_FILE 2>&1 &
 WEAVE_PID=$!
 
@@ -51,7 +58,7 @@ while true; do
     sleep 1
 done
 
-/home/weave/plugin --meshsocket='' --docker-api='' >/tmp/plugin.log 2>&1 &
+/home/weave/plugin --meshsocket='' --docker-api='' >/var/lib/weave/plugin.log 2>&1 &
 
 echo "End of launch.sh" >>$LOG_FILE
 

prog/weaveutil/main.go

@@ -37,6 +37,8 @@ func init() {
 		"expose-nat":             exposeNAT,
 		"bridge-ip":              bridgeIP,
 		"unique-id":              uniqueID,
+		"swarm-manager-peers":    swarmManagerPeers,
+		"is-swarm-manager":       isSwarmManager,
 	}
 }
 

prog/weaveutil/swarm.go

@@ -0,0 +1,64 @@
+package main
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/fsouza/go-dockerclient"
+	"github.com/pkg/errors"
+)
+
+const DOCKER_API_VERSION = "1.26"
+
+func isSwarmManager(args []string) error {
+	info, err := dockerInfo()
+	if err != nil {
+		return err
+	}
+
+	if !info.Swarm.ControlAvailable {
+		return fmt.Errorf("node is not a manager")
+	}
+
+	return nil
+}
+
+func swarmManagerPeers(args []string) error {
+	info, err := dockerInfo()
+	if err != nil {
+		return err
+	}
+
+	for _, managerNode := range info.Swarm.RemoteManagers {
+		ip, err := ipFromAddr(managerNode.Addr)
+		if err != nil {
+			return errors.Wrap(err, "ipFromAddr")
+		}
+		fmt.Println(ip)
+	}
+
+	return nil
+}
+
+func dockerInfo() (*docker.DockerInfo, error) {
+	client, err := docker.NewVersionedClientFromEnv(DOCKER_API_VERSION)
+	if err != nil {
+		return nil, errors.Wrap(err, "docker.NewVersionedClientFromEnv")
+	}
+
+	info, err := client.Info()
+	if err != nil {
+		return nil, errors.Wrap(err, "docker.Info")
+	}
+
+	return info, nil
+}
+
+func ipFromAddr(addr string) (string, error) {
+	parts := strings.Split(addr, ":")
+	if len(parts) != 2 {
+		return "", fmt.Errorf("invalid address: %q", addr)
+	}
+
+	return parts[0], nil
+}