00-memberlist.md

Shows how to connect Hashicorp's memberlist to Golang's groupcache for dynamic cluster membership. Memberlist gossip can be encrypted by setting the SecretKey or Keyring attributes on cfg.

01-main.go

package main

import (
	"github.com/golang/groupcache"
	"github.com/hashicorp/memberlist"
	"log"
	"net"
	"net/http"
	"time"
)

func main() {
	mux := http.DefaultServeMux
	port := "8080"

	httpAddress := func(ip string) string {
		return net.JoinHostPort(ip, port)
	}

	// sets up UDP/TCP server on 0.0.0.0:7946
	cfg := memberlist.DefaultLocalConfig()
	list, err := memberlist.Create(cfg)
	if err != nil {
		log.Fatal("cannot start memberlist servers", err)
	}

	// join existing members
	_, err = list.Join([]string{"discovery.address"})
	if err != nil {
		log.Fatal("cannot join memberlist server", err)
	}

	self := httpAddress(list.LocalNode().Addr.String())
	
	opts := &groupcache.HTTPPoolOptions{BasePath: "/_groupcache/"}
	pool := groupcache.NewHTTPPoolOpts(self, opts)
	mux.Handle(opts.BasePath, pool)

	// setup background worker
	go func() {
		for {
			// update groupcache peers based on memberlist every 5 seconds
			<- time.Tick(5 * time.Second)

			members := list.Members()
			peers := make([]string, 0, len(members))
			for _, member := range members {
				peer := httpAddress(member.Addr.String())
				if peer != self {
					peers = append(peers, self)
				}
			}

			pool.Set(peers...)
		}
	}()
	
	// cache of 64MB
	group := groupcache.NewGroup("name", 64 << 20, groupcache.GetterFunc(
		func(ctx context.Context, key string, dest Sink) error {
			// cache miss
			// dest.SetString(str)
			// dest.SetProto(msg)
			return nil
		}
	))
	// err := group.Get(ctx, "key", groupcache.StringSink(&str))
	// err := group.Get(ctx, "key", groupcache.ProtoSink(msg))

	// sets up HTTP server on 0.0.0.0:8080
	if err := http.ListenAndServe(httpAddress("0.0.0.0"), mux); err != nil {
		log.Fatal("cannot start http server", err)
	}
}