server: add cluster config

cli/agent/command.go

@@ -101,7 +101,6 @@ Heartbeat interval in seconds.
 To verify the connection to the server is ok, the listener sends a
 heartbeat to the upstream at the '--server.heartbeat-interval-seconds'
 interval, with a timeout of '--server.heartbeat-timeout-seconds'.`,
-
 	)
 	cmd.Flags().IntVar(
 		&conf.Server.HeartbeatTimeoutSeconds,
@@ -143,7 +142,7 @@ The available levels are 'debug', 'info', 'warn' and 'error'.`,
 		"log.subsystems",
 		nil,
 		`
-Each log has a 'subsystem' field where the log occured. 
+Each log has a 'subsystem' field where the log occured.
 
 '--log.subsystems' enables all log levels for those given subsystems. This
 can be useful to debug a particular subsystem without having to enable all

cli/server/command.go

@@ -31,14 +31,19 @@ func NewCommand() *cobra.Command {
 The Pico server is responsible for proxying requests from downstream clients to
 registered upstream listeners.
 
-Note Pico does not yet support a cluster of nodes.
+Pico may run as a cluster of nodes for fault tolerance and scalability. Use
+'--cluster.members' to configure addresses of existing members in the cluster
+to join.
 
 Examples:
-  # Start a pico server on :8080
+  # Start a Pico server on :8080
   pico server
 
-  # Start a pico server on :7000.
-  pico server --server.addr :7000
+  # Start a Pico server on :7000.
+  pico server --server.listen-addr :7000
+
+  # Start a Pico server and join an existing cluster.
+  pico server --cluster.members 10.26.104.14,10.26.104.75
 `,
 	}
 
@@ -53,8 +58,19 @@ The host/port to listen on for incoming HTTP and WebSocket connections from
 both downstream clients and upstream listeners.
 
 If the host is unspecified it defaults to all listeners, such as
-'--server.addr :8080' will listen on '0.0.0.0:8080'`,
+'--server.listen-addr :8080' will listen on '0.0.0.0:8080'`,
+	)
+	cmd.Flags().StringVar(
+		&conf.Server.GossipAddr,
+		"server.gossip-addr",
+		":7000",
+		`
+The host/port to listen for inter-node gossip traffic.
+
+If the host is unspecified it defaults to all listeners, such as
+'--server.gossip-addr :7000' will listen on '0.0.0.0:7000'`,
 	)
+
 	cmd.Flags().IntVar(
 		&conf.Server.GracePeriodSeconds,
 		"server.grace-period-seconds",
@@ -68,6 +84,25 @@ connections to upstream listeners, announcing to the cluster the node is
 leaving...`,
 	)
 
+	cmd.Flags().StringSliceVar(
+		&conf.Cluster.Members,
+		"cluster.members",
+		nil,
+		`
+A list of addresses of members in the cluster to join.
+
+This may be either addresses of specific nodes, such as
+'--cluster.members 10.26.104.14,10.26.104.75', or a domain that resolves to
+the addresses of the nodes in the cluster (e.g. a Kubernetes headless
+service), such as '--cluster.members pico.prod-pico-ns'.
+
+Each address must include the host, and may optionally include a port. If no
+port is given, the gossip port of this node is used.
+
+Note each node propagates membership information to the other known nodes,
+so the initial set of configured members only needs to be a subset of nodes.`,
+	)
+
 	cmd.Flags().IntVar(
 		&conf.Proxy.TimeoutSeconds,
 		"proxy.timeout-seconds",

server/config/config.go

@@ -8,12 +8,22 @@ package config
 import "fmt"
 
 type ServerConfig struct {
+	// ListenAddr is the address to listen for incoming HTTP and WebSocket
+	// connections.
 	ListenAddr string `json:"listen_addr"`
+
+	// GossipAddr is the address to listen for incoming UDP gossip messages.
+	GossipAddr string `json:"gossip_addr"`
+
 	// GracePeriodSeconds is the maximum number of seconds to gracefully
 	// shutdown after receiving a shutdown signal.
 	GracePeriodSeconds int `json:"grace_period_seconds"`
 }
 
+type ClusterConfig struct {
+	Members []string `json:"members"`
+}
+
 func (c *ServerConfig) Validate() error {
 	if c.ListenAddr == "" {
 		return fmt.Errorf("missing listen addr")
@@ -63,6 +73,7 @@ func (c *LogConfig) Validate() error {
 
 type Config struct {
 	Server   ServerConfig   `json:"server"`
+	Cluster  ClusterConfig  `json:"cluster"`
 	Proxy    ProxyConfig    `json:"proxy"`
 	Upstream UpstreamConfig `json:"upstream"`
 	Log      LogConfig      `json:"log"`