main.go

package main

import (
    "os"
    "log"
    
    flags "github.com/jessevdk/go-flags"
    dockerapi "github.com/fsouza/go-dockerclient"
)

func getopt(name, def string) string {
    if env := os.Getenv(name); env != "" {
        return env
    }
    
    return def
}

func assert(err error) {
    if err != nil {
        log.Fatal("docker-hosts: ", err)
    }
}

type Options struct {
	DomainName string `short:"d" long:"domain-name" description:"domain to append"`
	File struct {
		Filename string
	} `positional-args:"true" required:"true" description:"the hosts file to write"`
}

func main() {
	var opts Options
	
	_, err := flags.Parse(&opts)
	if err != nil {
		os.Exit(1)
	}
	
    docker, err := dockerapi.NewClient(getopt("DOCKER_HOST", "unix:///var/run/docker.sock"))
    assert(err)

    hosts := NewHosts(docker, opts.File.Filename, opts.DomainName)

    // set up to handle events early, so we don't miss anything while doing the
    // initial population
    events := make(chan *dockerapi.APIEvents)
    assert(docker.AddEventListener(events))

    containers, err := docker.ListContainers(dockerapi.ListContainersOptions{})
    assert(err)

    for _, listing := range containers {
        go hosts.Add(listing.ID)
    }

    log.Println("docker-hosts: Listening for Docker events...")
    for msg := range events {
        switch msg.Status {
        case "start":
            go hosts.Add(msg.ID)

        case "die":
            go hosts.Remove(msg.ID)
        }
    }

    log.Fatal("docker-hosts: docker event loop closed") // todo: reconnect?
}