Merge pull request #1 from ifwe/add-redecs-agent

Add redecs_agent

redecs_agent.go

@@ -0,0 +1,142 @@
+package main
+
+// Originally adapted from https://github.com/awslabs/service-discovery-ecs-dns
+// This service is intended to run on AWS ECS instances. It will look for special
+// SERVICE environment variables and add those services to a Redis ZSET with the
+// timestamp as the key. The accompanying service, red53_agent will check this
+// ZSET and write changes to AWS Route53.
+
+import (
+	"errors"
+	"fmt"
+	log "github.com/Sirupsen/logrus"
+	"github.com/aws/aws-sdk-go/aws/ec2metadata"
+	"github.com/aws/aws-sdk-go/aws/session"
+	"github.com/fsouza/go-dockerclient"
+	"gopkg.in/redis.v5"
+	"os"
+	"strconv"
+	"strings"
+	"time"
+)
+
+type config struct {
+	EcsCluster string
+	Region     string
+	LocalIp    string
+	RedisHost  string
+}
+
+var configuration config
+
+func logErrorAndFail(err error) {
+	if err != nil {
+		log.Fatal(err)
+	}
+}
+
+func logErrorNoFatal(err error) {
+	if err != nil {
+		log.Error(err)
+	}
+}
+
+var dockerClient *docker.Client
+var redisClient *redis.Client
+
+func reportServiceActive(serviceName string) {
+	log.Debug("Reporting " + serviceName + " as active with IP " + configuration.LocalIp)
+	// write {timestamp => SERVICENAME_IP} to ecssd:service_pings
+	redisClient.ZAddNX("redecs:service_pings", redis.Z{float64(time.Now().Unix()), serviceName + "_" + configuration.LocalIp})
+}
+
+func getServiceName(container *docker.Container) string {
+	// One of the environment variables should be SERVICE_<port>_NAME = <name of the service>
+	// We look for this environment variable doing a split in the "=" and another one in the "_"
+	// So envEval = [SERVICE_<port>_NAME, <name>]
+	// nameEval = [SERVICE, <port>, NAME]
+	for _, env := range container.Config.Env {
+		envEval := strings.Split(env, "=")
+		nameEval := strings.Split(envEval[0], "_")
+		if len(envEval) == 2 && len(nameEval) == 3 && nameEval[0] == "SERVICE" && nameEval[2] == "NAME" {
+			if _, err := strconv.Atoi(nameEval[1]); err == nil {
+				return envEval[1]
+			}
+		}
+	}
+	return ""
+}
+
+func processContainers() {
+	log.Debug("Listing active containers...")
+
+	// only get running ones
+	containers, err := dockerClient.ListContainers(docker.ListContainersOptions{All: false})
+	// bail out completely if we can't list containers.
+	logErrorAndFail(err)
+	for _, containerEntry := range containers {
+		// have to inspect to get the environment variable
+		container, err := dockerClient.InspectContainer(containerEntry.ID)
+		// retry logic?
+		logErrorAndFail(err)
+		serviceName := getServiceName(container)
+		if serviceName != "" {
+			reportServiceActive(serviceName)
+		}
+	}
+
+	log.Debug("Done checking active containers")
+}
+
+func main() {
+	var err error
+	var sum int
+	if len(os.Args) < 2 || len(os.Args) > 3 {
+		err = errors.New(fmt.Sprintf("Usage: %s [Redis host] {host IP (for testing)}\n", os.Args[0]))
+		logErrorAndFail(err)
+	}
+	if len(os.Args) == 3 {
+		configuration.LocalIp = os.Args[2]
+	} else {
+		metadataClient := ec2metadata.New(session.New())
+		localIp, err := metadataClient.GetMetadata("/local-ipv4")
+		logErrorAndFail(err)
+		configuration.LocalIp = localIp
+	}
+	configuration.RedisHost = os.Args[1]
+	endpoint := "unix:///var/run/docker.sock"
+	dockerClient, err = docker.NewClient(endpoint)
+
+	// bail out if we can't talk to Docker
+	logErrorAndFail(err)
+
+	sum = 1
+	for {
+		// We try to get the Redis connection using exponential backoff
+		redisClient = redis.NewClient(&redis.Options{
+			Addr:       configuration.RedisHost + ":6379",
+			Password:   "", // none
+			DB:         0,  // default DB
+			MaxRetries: 3,
+		})
+		// Check the connection.
+		err := redisClient.Ping().Err()
+
+		if err == nil {
+			break
+		}
+		if sum > 8 {
+			logErrorAndFail(err)
+		}
+		time.Sleep(time.Duration(sum) * time.Second)
+		sum += 2
+	}
+
+	// continue processing once per minute
+	ticker := time.NewTicker(time.Second * 60)
+
+	for {
+		processContainers()
+		<-ticker.C
+	}
+}