server: add node id prefix flag

cli/server/command.go

@@ -106,7 +106,11 @@ default value can be given using form ${VAR:default}.`,
 		}
 
 		if conf.Cluster.NodeID == "" {
-			conf.Cluster.NodeID = netmap.GenerateNodeID()
+			nodeID := netmap.GenerateNodeID()
+			if conf.Cluster.NodeIDPrefix != "" {
+				nodeID = conf.Cluster.NodeIDPrefix + nodeID
+			}
+			conf.Cluster.NodeID = nodeID
 		}
 
 		if conf.Proxy.AdvertiseAddr == "" {

server/config/config.go

@@ -75,6 +75,10 @@ type ClusterConfig struct {
 	// NodeID is a unique identifier for this node in the cluster.
 	NodeID string `json:"node_id" yaml:"node_id"`
 
+	// NodeIDPrefix is a node ID prefix, where Pico will generate the rest of
+	// the node ID to ensure uniqueness.
+	NodeIDPrefix string `json:"node_id_prefix" yaml:"node_id_prefix"`
+
 	// Join contians a list of addresses of members in the cluster to join.
 	Join []string `json:"join" yaml:"join"`
 }
@@ -249,6 +253,20 @@ A unique identifier for the node in the cluster.
 
 By default a random ID will be generated for the node.`,
 	)
+	fs.StringVar(
+		&c.Cluster.NodeIDPrefix,
+		"cluster.node-id-prefix",
+		"",
+		`
+A prefix for the node ID.
+
+Pico will generate a unique random identifier for the node and append it to
+the given prefix.
+
+Such as you could use the node or pod  name as a prefix, then add a unique
+identifier to ensure the node ID is unique across restarts.`,
+	)
+
 	fs.StringSliceVar(
 		&c.Cluster.Join,
 		"cluster.join",

server/netmap/node.go

@@ -70,7 +70,7 @@ func (n *Node) Copy() *Node {
 }
 
 func GenerateNodeID() string {
-	b := make([]byte, 10)
+	b := make([]byte, 6)
 	for i := range b {
 		n, err := rand.Int(rand.Reader, big.NewInt(int64(len(alphaNumericChars))))
 		if err != nil {