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Published: May 29, 2023 License: MIT Imports: 13 Imported by: 48



Package etcd provides an Instancer and Registrar implementation for etcd. If you use etcd as your service discovery system, this package will help you implement the registration and client-side load balancing patterns.

package main

import (


func main() {
	// Let's say this is a service that means to register itself.
	// First, we will set up some context.
	var (
		etcdServer = "" // don't forget schema and port!
		prefix     = "/services/foosvc/"    // known at compile time
		instance   = ""         // taken from runtime or platform, somehow
		key        = prefix + instance      // should be globally unique
		value      = "http://" + instance   // based on our transport
		ctx        = context.Background()

	// Build the client.
	client, err := NewClient(ctx, []string{etcdServer}, ClientOptions{})
	if err != nil {

	// Build the registrar.
	registrar := NewRegistrar(client, Service{
		Key:   key,
		Value: value,
	}, log.NewNopLogger())

	// Register our instance.

	// At the end of our service lifecycle, for example at the end of func main,
	// we should make sure to deregister ourselves. This is important! Don't
	// accidentally skip this step by invoking a log.Fatal or os.Exit in the
	// interim, which bypasses the defer stack.
	defer registrar.Deregister()

	// It's likely that we'll also want to connect to other services and call
	// their methods. We can build an Instancer to listen for changes from etcd,
	// create Endpointer, wrap it with a load-balancer to pick a single
	// endpoint, and finally wrap it with a retry strategy to get something that
	// can be used as an endpoint directly.
	barPrefix := "/services/barsvc"
	logger := log.NewNopLogger()
	instancer, err := NewInstancer(client, barPrefix, logger)
	if err != nil {
	endpointer := sd.NewEndpointer(instancer, barFactory, logger)
	balancer := lb.NewRoundRobin(endpointer)
	retry := lb.Retry(3, 3*time.Second, balancer)

	// And now retry can be used like any other endpoint.
	req := struct{}{}
	if _, err = retry(ctx, req); err != nil {

func barFactory(string) (endpoint.Endpoint, io.Closer, error) { return endpoint.Nop, nil, nil }




This section is empty.


View Source
var (
	// ErrNoKey indicates a client method needs a key but receives none.
	ErrNoKey = errors.New("no key provided")

	// ErrNoValue indicates a client method needs a value but receives none.
	ErrNoValue = errors.New("no value provided")


This section is empty.


type Client

type Client interface {
	// GetEntries queries the given prefix in etcd and returns a slice
	// containing the values of all keys found, recursively, underneath that
	// prefix.
	GetEntries(prefix string) ([]string, error)

	// WatchPrefix watches the given prefix in etcd for changes. When a change
	// is detected, it will signal on the passed channel. Clients are expected
	// to call GetEntries to update themselves with the latest set of complete
	// values. WatchPrefix will always send an initial sentinel value on the
	// channel after establishing the watch, to ensure that clients always
	// receive the latest set of values. WatchPrefix will block until the
	// context passed to the NewClient constructor is terminated.
	WatchPrefix(prefix string, ch chan struct{})

	// Register a service with etcd.
	Register(s Service) error

	// Deregister a service with etcd.
	Deregister(s Service) error

Client is a wrapper around the etcd client.

func NewClient

func NewClient(ctx context.Context, machines []string, options ClientOptions) (Client, error)

NewClient returns Client with a connection to the named machines. It will return an error if a connection to the cluster cannot be made. The parameter machines needs to be a full URL with schemas. e.g. "http://localhost:2379" will work, but "localhost:2379" will not.

type ClientOptions

type ClientOptions struct {
	Cert                    string
	Key                     string
	CACert                  string
	DialTimeout             time.Duration
	DialKeepAlive           time.Duration
	HeaderTimeoutPerRequest time.Duration

ClientOptions defines options for the etcd client. All values are optional. If any duration is not specified, a default of 3 seconds will be used.

type Instancer added in v0.5.0

type Instancer struct {
	// contains filtered or unexported fields

Instancer yields instances stored in a certain etcd keyspace. Any kind of change in that keyspace is watched and will update the Instancer's Instancers.

func NewInstancer added in v0.5.0

func NewInstancer(c Client, prefix string, logger log.Logger) (*Instancer, error)

NewInstancer returns an etcd instancer. It will start watching the given prefix for changes, and update the subscribers.

func (*Instancer) Deregister added in v0.5.0

func (s *Instancer) Deregister(ch chan<- sd.Event)

Deregister implements Instancer.

func (*Instancer) Register added in v0.5.0

func (s *Instancer) Register(ch chan<- sd.Event)

Register implements Instancer.

func (*Instancer) Stop added in v0.5.0

func (s *Instancer) Stop()

Stop terminates the Instancer.

type Registrar added in v0.2.0

type Registrar struct {
	// contains filtered or unexported fields

Registrar registers service instance liveness information to etcd.

func NewRegistrar added in v0.2.0

func NewRegistrar(client Client, service Service, logger log.Logger) *Registrar

NewRegistrar returns a etcd Registrar acting on the provided catalog registration (service).

func (*Registrar) Deregister added in v0.2.0

func (r *Registrar) Deregister()

Deregister implements the sd.Registrar interface. Call it when you want your service to be deregistered from etcd, typically just prior to shutdown.

func (*Registrar) Register added in v0.2.0

func (r *Registrar) Register()

Register implements the sd.Registrar interface. Call it when you want your service to be registered in etcd, typically at startup.

type Service added in v0.2.0

type Service struct {
	Key           string // unique key, e.g. "/service/foobar/"
	Value         string // returned to subscribers, e.g. ""
	TTL           *TTLOption
	DeleteOptions *etcd.DeleteOptions

Service holds the instance identifying data you want to publish to etcd. Key must be unique, and value is the string returned to subscribers, typically called the "instance" string in other parts of package sd.

type TTLOption added in v0.4.0

type TTLOption struct {
	// contains filtered or unexported fields

TTLOption allow setting a key with a TTL. This option will be used by a loop goroutine which regularly refreshes the lease of the key.

func NewTTLOption added in v0.4.0

func NewTTLOption(heartbeat, ttl time.Duration) *TTLOption

NewTTLOption returns a TTLOption that contains proper TTL settings. Heartbeat is used to refresh the lease of the key periodically; its value should be at least 500ms. TTL defines the lease of the key; its value should be significantly greater than heartbeat.

Good default values might be 3s heartbeat, 10s TTL.

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