mcset

go.serversets/mcset

Package mcset provides consistent sharding over a set of memcache nodes provided by go.serversets.

Consistent hashing is provided by github.com/stathat/consistent and the MCSet object fulfills the ServerSelector interface to be used with github.com/bradfitz/gomemcache/memcache.

Client Usage

package main

import (
	"log"

	"github.com/bradfitz/gomemcache/memcache"
	"github.com/strava/go.serversets"
	"github.com/strava/go.serversets/mcset"
)

func main() {
	zookeepers := []string{"10.0.1.0", "10.0.5.0", "10.0.9.0"}
	watch, err := serversets.New(serversets.Production, "memcache_nodes", zookeepers).Watch()
	if err != nil {
		// This will be a problem connecting to Zookeeper
		log.Fatalf("Registration error: %v", err)
	}

	cluster := mcset.New(watch)
	memcacheClient := memcache.NewFromSelector(cluster)

	// key will be consistently hash over the current set of servers
	item, err := memcacheClient.Get("key")

	log.Print(item, err)
}

Memcache node registration

package main

import (
	"log"
	"net"
	"os"

	"github.com/bradfitz/gomemcache/memcache"
	"github.com/strava/go.serversets"
)

func main() {
	localHostname, err := os.Hostname()
	if err != nil {
		log.Fatalf("Unable to determine hostname: %v", err)
	}

	// define a "ping" function
	localClient := memcache.New(net.JoinHostPort(localHostname, "11211"))
	pingFunc := func() error {
		_, err := localClient.Get("ping")
		if err == nil || err == memcache.ErrCacheMiss {
			return nil
		}

		log.Printf("Memcache error: %v", err)
		return err
	}

	// register the endpoint to the zookeepers
	zookeepers := []string{"10.0.1.0", "10.0.5.0", "10.0.9.0"}
	endpoint, err := serversets.New(serversets.Production, "memcache_nodes", zookeepers).
		RegisterEndpoint(localHostname, 11211, pingFunc)

	if err != nil {
		// This will be a problem connecting to Zookeeper
		log.Fatalf("Registration error: %v", err)
	}

	log.Printf("Registered as %s:11211", localHostname)

	// will will wait forever, since you'll never actually close the endpoint
	<-endpoint.CloseEvent
}

Dependencies

• github.com/strava/go.serversets to get the server list
• github.com/stathat/consistent for consistent hashing