sablier/main.go

package main

import (
	"flag"
	"fmt"
	"log"
	"net/http"
	"net/url"
	"time"

	"github.com/acouvreur/traefik-ondemand-service/pkg/scaler"
	"github.com/docker/docker/client"
	"gopkg.in/dc0d/tinykv.v4"
)

var defaultTimeout = time.Second * 5

type OnDemandRequestState struct {
	State string `json:"state"`
	Name  string `json:"name"`
}

func main() {

	swarmMode := flag.Bool("swarmMode", true, "Enable swarm mode")

	flag.Parse()

	cli, err := client.NewClientWithOpts()
	if err != nil {
		log.Fatal(fmt.Errorf("%+v", "Could not connect to docker API"))
	}

	dockerScaler := getDockerScaler(*swarmMode)

	fmt.Printf("Server listening on port 10000, swarmMode: %t\n", *swarmMode)
	http.HandleFunc("/", onDemand(cli, dockerScaler))
	log.Fatal(http.ListenAndServe(":10000", nil))
}

func getDockerScaler(swarmMode bool) scaler.Scaler {
	if swarmMode {
		return scaler.DockerSwarmScaler{}
	}
	return scaler.DockerClassicScaler{}
}

func onDemand(client *client.Client, scaler scaler.Scaler) func(w http.ResponseWriter, r *http.Request) {

	store := tinykv.New(time.Second*20, func(key string, _ interface{}) {
		// Auto scale down after timeout
		scaler.ScaleDown(client, key)
	})

	return func(rw http.ResponseWriter, r *http.Request) {

		name, err := getParam(r.URL.Query(), "name")

		if err != nil {
			ServeHTTPInternalError(rw, err)
			return
		}

		to, err := getParam(r.URL.Query(), "timeout")

		if err != nil {
			ServeHTTPInternalError(rw, err)
			return
		}

		timeout, err := time.ParseDuration(to)

		if err != nil {
			ServeHTTPInternalError(rw, err)
			return
		}

		replicas := uint64(1)

		requestState, exists := store.Get(name)

		// 1. Check against the current state
		if !exists || requestState.(OnDemandRequestState).State != "started" {
			if scaler.IsUp(client, name) {
				requestState = OnDemandRequestState{
					State: "started",
					Name:  name,
				}
			} else {
				requestState = OnDemandRequestState{
					State: "starting",
					Name:  name,
				}
				scaler.ScaleUp(client, name, &replicas)
			}
		}

		// 2. Store the updated state
		store.Put(name, requestState, tinykv.ExpiresAfter(timeout))

		// 3. Serve depending on the current state
		switch requestState.(OnDemandRequestState).State {
		case "starting":
			ServeHTTPRequestState(rw, requestState.(OnDemandRequestState))
		case "started":
			ServeHTTPRequestState(rw, requestState.(OnDemandRequestState))
		default:
			ServeHTTPInternalError(rw, fmt.Errorf("unknown state %s", requestState.(OnDemandRequestState).State))
		}
	}
}

func getParam(queryParams url.Values, paramName string) (string, error) {
	if queryParams[paramName] == nil {
		return "", fmt.Errorf("%s is required", paramName)
	}
	return queryParams[paramName][0], nil
}

func ServeHTTPInternalError(rw http.ResponseWriter, err error) {
	rw.WriteHeader(http.StatusInternalServerError)
	rw.Write([]byte(err.Error()))
}

func ServeHTTPRequestState(rw http.ResponseWriter, requestState OnDemandRequestState) {
	rw.Header().Set("Content-Type", "text/plain")
	if requestState.State == "started" {
		rw.WriteHeader(http.StatusCreated)
	} else {
		rw.WriteHeader(http.StatusAccepted)
	}
	rw.Write([]byte(requestState.State))
}