gossip: add gossip interface

cli/server/command.go

@@ -11,6 +11,8 @@ import (
 	"github.com/andydunstall/pico/pkg/log"
 	"github.com/andydunstall/pico/server"
 	"github.com/andydunstall/pico/server/config"
+	"github.com/andydunstall/pico/server/gossip"
+	"github.com/andydunstall/pico/server/netmap"
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/spf13/cobra"
 	"go.uber.org/zap"
@@ -183,6 +185,11 @@ func run(conf *config.Config, logger *log.Logger) {
 		logger,
 	)
 
+	netmap := netmap.NewNetworkMap()
+	// TODO(andydunstall): Should wait for gossip to join and sync before
+	// the server becomes ready.
+	gossip := gossip.NewGossip(netmap, logger)
+
 	ctx, cancel := signal.NotifyContext(
 		context.Background(), syscall.SIGINT, syscall.SIGTERM,
 	)
@@ -211,6 +218,12 @@ func run(conf *config.Config, logger *log.Logger) {
 		}
 		return nil
 	})
+	g.Go(func() error {
+		if err := gossip.Run(ctx); err != nil {
+			return fmt.Errorf("gossip: %w", err)
+		}
+		return nil
+	})
 
 	if err := g.Wait(); err != nil {
 		logger.Error("failed to run server", zap.Error(err))

server/gossip/gossip.go

@@ -0,0 +1,29 @@
+package gossip
+
+import (
+	"context"
+
+	"github.com/andydunstall/pico/pkg/log"
+	"github.com/andydunstall/pico/server/netmap"
+)
+
+// Gossip is responsible for maintaining the nodes local NetworkMap and
+// propagating the state of the local node to the rest of the cluster.
+type Gossip struct {
+	netmap *netmap.NetworkMap
+	logger *log.Logger
+}
+
+// NewGossip initializes gossip to maintain the given network map.
+func NewGossip(netmap *netmap.NetworkMap, logger *log.Logger) *Gossip {
+	return &Gossip{
+		netmap: netmap,
+		logger: logger.WithSubsystem("gossip"),
+	}
+}
+
+// Run gossips with the other nodes in the cluster until cancelled.
+func (g *Gossip) Run(_ context.Context) error {
+	g.logger.Info("starting gossip")
+	return nil
+}

server/netmap/netmap.go

@@ -0,0 +1,13 @@
+package netmap
+
+// NetworkMap represents the known state of the cluster as seen by the local
+// node.
+//
+// This map is eventually consistent. The state is propagated among the nodes
+// in the cluster using gossip.
+type NetworkMap struct {
+}
+
+func NewNetworkMap() *NetworkMap {
+	return &NetworkMap{}
+}

server/netmap/node.go

@@ -0,0 +1,17 @@
+package netmap
+
+// Node represents the known state about a node in the cluster.
+type Node struct {
+	// ID is a unique identifier for the node in the cluster.
+	ID string
+
+	// HTTPAddr is the advertised HTTP address
+	HTTPAddr string
+
+	// GossipAddr is the advertised gossip address.
+	GossipAddr string
+
+	// Endpoints contains the active endpoints on the node. This maps the
+	// active endpoint ID to the number of listeners for that endpoint.
+	Endpoints map[string]int
+}