chetcd

chetcd

Config-helpers for etcd. The aim is to have some common etcd-client use cases wrapper in an elegant API.

Dir watcher

A dir watcher will simply watch a (directory) key recursively. We can attach key observers to receive these changes via native golang channels.

A typical usage would be if we have a directory for all our config values of the application. We want to watch all those config values and react on them to update our live instance.

Quick Start

Source

go get -u github.com/coreos/etcd go get -u github.com/francoishill/chetcd

Usage

package main

import (
    "fmt"
    "github.com/coreos/etcd/client"
    "github.com/francoishill/chetcd"
    "log"
    "time"
)

func main() {
    cfg := client.Config{
        Endpoints:               []string{"http://127.0.0.1:2379"},
        Transport:               client.DefaultTransport,
        HeaderTimeoutPerRequest: time.Second, // set timeout per request to fail fast when the target endpoint is unavailable
    }

    c, err := client.New(cfg)
    if err != nil {
        log.Fatal(err)
    }

    keysAPI := client.NewKeysAPI(c)

    foodirWatcher := chetcd.NewDirWatcher(keysAPI, "/foodir")

    bar1ConfigValue, err := foodirWatcher.GetObservedConfigValue("/bar1")
    if err != nil {
        log.Fatal(err)
    }

    bar2ConfigValue, err := foodirWatcher.GetObservedConfigValue("/bar2")
    if err != nil {
        log.Fatal(err)
    }

    go func() {
        for {
            select {
            case b1 := <-bar1ConfigValue.ChangesChannel():
                fmt.Printf("Bar 1 changed from '%s' to '%s'\n", b1.OldNode.Value, b1.NewNode.Value)
                break
            case b2 := <-bar2ConfigValue.ChangesChannel():
                fmt.Printf("Bar 2 changed from '%s' to '%s'\n", b2.OldNode.Value, b2.NewNode.Value)
                break
            }
        }
    }()

    //The delay to wait when we receive `watcher.Next()` errors. This could be because the etcd server is down.
    delayOnError := 30 * time.Second
    errChan := foodirWatcher.WatchDir(delayOnError)
    for er := range errChan {
        fmt.Printf("DIR WATCH ERROR: %s, watcher: %q\n", er.Error(), foodirWatcher)
    }
}