docker-event-handler/main.go

package main

import (
	"bytes"
	"context"
	"errors"
	"fmt"
	"github.com/docker/docker/api/types/filters"
	"gopkg.in/ini.v1"
	"log"
	"os"
	"os/exec"
	"strconv"
	"strings"
	"text/template"
	"time"

	"github.com/docker/docker/api/types"
	"github.com/docker/docker/api/types/events"
	"github.com/docker/docker/client"
	"github.com/docker/go-connections/nat"
	"github.com/google/shlex"
	"github.com/ryanuber/go-glob"
)

type Configuration struct {
	handlers []Handler
}

type ContainerEvent struct {
	Action    string
	Name      string
	ID        string
	Image     string
	Labels    map[string]string
	Mounts    []types.MountPoint
	Hostname  string
	IPAddress string
	Ports     nat.PortMap
}

type Handler struct {
	Action   []string
	Name     []string
	Image    []string
	ID       []string
	Hostname []string
	Label    map[string]*string
	Handler  *template.Template
}

func (h Handler) matches(e ContainerEvent) bool {
	if !stringListMatches(h.Action, e.Action) {
		return false
	}
	if !stringListMatches(h.Name, e.Name) {
		return false
	}
	if !stringListMatches(h.Image, e.Image) {
		return false
	}
	if !stringListMatches(h.ID, e.ID) {
		return false
	}
	if !stringListMatches(h.Hostname, e.Hostname) {
		return false
	}

	for key, val := range h.Label {
		actualVal, exists := e.Labels[key]
		if !exists {
			return false
		}
		if val != nil {
			if actualVal != *val {
				return false
			}
		}
	}

	return true
}

func (h Handler) invoke(e ContainerEvent) error {
	var cmdBuf bytes.Buffer
	err := h.Handler.Execute(&cmdBuf, e)
	if err != nil {
		return err
	}
	parts, err := shlex.Split(cmdBuf.String())
	if err != nil {
		return err
	}

	if len(parts) < 1 {
		return errors.New("no handler given")
	}
	name := parts[0]
	args := parts[1:]

	return exec.Command(name, args...).Run()
}

func stringListMatches(list []string, subject string) bool {
	if len(list) == 0 {
		return true
	}
	for _, pattern := range list {
		if glob.Glob(pattern, subject) {
			return true
		}
	}
	return false
}

func handleEvent(dockerClient *client.Client, event events.Message, handlers []Handler) {
	if event.Type != "container" { // only container events are currently supported
		return
	}
	if event.Action == "destroy" { // destroy event is not supported because the container can't be inspected
		return
	}

	container, err := dockerClient.ContainerInspect(context.TODO(), event.Actor.ID)
	if err != nil {
		log.Printf("error inspecting container %v: %v", event.Actor.ID, err)
		return
	}

	ev := ContainerEvent{
		Action:    event.Action,
		Name:      container.Name,
		ID:        event.Actor.ID,
		Image:     container.Config.Image,
		Labels:    container.Config.Labels,
		Mounts:    container.Mounts,
		Hostname:  container.Config.Hostname,
		IPAddress: container.NetworkSettings.IPAddress,
		Ports:     container.NetworkSettings.Ports,
	}

	for _, handler := range handlers {
		if handler.matches(ev) {
			err := handler.invoke(ev)
			if err != nil {
				log.Printf("error invoking handler: %v", err)
			}
		}
	}
}

func readConfiguration(path string) (Configuration, error) {
	var config Configuration
	cfg, err := ini.LoadSources(ini.LoadOptions{
		AllowNonUniqueSections: true,
		AllowShadows:           true,
	}, path)
	if err != nil {
		return config, err
	}

	for _, section := range cfg.Sections() {
		if section.Name() == "Handler" {
			var handler Handler
			handler.Label = make(map[string]*string)
			for _, key := range section.Keys() {
				val := key.String()
				switch key.Name() {
				case "Action":
					handler.Action = append(handler.Action, val)
					break
				case "Name":
					handler.Name = append(handler.Name, val)
					break
				case "Image":
					handler.Image = append(handler.Image, val)
					break
				case "ID":
					handler.ID = append(handler.ID, val)
					break
				case "Hostname":
					handler.Hostname = append(handler.Hostname, val)
					break
				case "Label":
					parts := strings.SplitN(val, "=", 2)
					var k string
					var v *string
					if len(parts) == 2 {
						k = parts[0]
						v = &parts[1]
					} else {
						k = parts[0]
						v = nil
					}
					handler.Label[k] = v
					break
				case "Run":
					if handler.Handler != nil {
						return config, errors.New(fmt.Sprintf("duplicate key %v in section %v", key.Name(), section.Name()))
					}
					handler.Handler, err = template.New("Handler").Parse(val)
					if err != nil {
						return config, err
					}
					break
				default:
					return config, errors.New(fmt.Sprintf("unknown key %v in section %v", key.Name(), section.Name()))
				}
			}
			config.handlers = append(config.handlers, handler)
		}
	}
	return config, nil
}

func main() {
	configPath := "/etc/docker-event-handler.conf"

	if len(os.Args) > 1 {
		if len(os.Args) > 2 {
			log.Fatal("too many arguments")
		}
		configPath = os.Args[1]
	}

	config, err := readConfiguration(configPath)
	if err != nil {
		log.Fatal("configuration parsing failed", err)
	}

	dockerClient, err := client.NewClientWithOpts(client.WithAPIVersionNegotiation())
	if err != nil {
		log.Fatal("docker connection failed", err)
	}

	evs, errs := dockerClient.Events(context.TODO(), types.EventsOptions{
		Since: strconv.FormatInt(time.Now().Unix(), 10),
		Filters: filters.NewArgs(
			filters.Arg("type", events.ContainerEventType),
		),
	})

	for {
		select {
		case err := <-errs:
			log.Fatal("event stream failed", err)
		case event := <-evs:
			handleEvent(dockerClient, event, config.handlers)
		}
	}

}