Add comment to explain how method works

Signed-off-by: Alex Ellis (OpenFaaS Ltd) <alexellis2@gmail.com>

cmd/provider.go

@@ -98,7 +98,7 @@ func makeProviderCmd() *cobra.Command {
 			DeployHandler:        handlers.MakeDeployHandler(client, cni, baseUserSecretsPath, alwaysPull),
 			FunctionReader:       handlers.MakeReadHandler(client),
 			ReplicaReader:        handlers.MakeReplicaReaderHandler(client),
-			ReplicaUpdater:       handlers.MakeReplicaUpdateHandler(client, cni),
+			ReplicaUpdater:       handlers.MakeReplicaUpdateHandler(client, cni, invokeResolver),
 			UpdateHandler:        handlers.MakeUpdateHandler(client, cni, baseUserSecretsPath, alwaysPull),
 			HealthHandler:        func(w http.ResponseWriter, r *http.Request) {},
 			InfoHandler:          handlers.MakeInfoHandler(Version, GitCommit),

pkg/provider/handlers/scale.go

@@ -6,16 +6,20 @@ import (
 	"fmt"
 	"io/ioutil"
 	"log"
+	"net"
 	"net/http"
+	"net/url"
+	"time"
 
 	"github.com/containerd/containerd"
 	"github.com/containerd/containerd/namespaces"
 	gocni "github.com/containerd/go-cni"
 
+	"github.com/openfaas/faas-provider/proxy"
 	"github.com/openfaas/faas-provider/types"
 )
 
-func MakeReplicaUpdateHandler(client *containerd.Client, cni gocni.CNI) func(w http.ResponseWriter, r *http.Request) {
+func MakeReplicaUpdateHandler(client *containerd.Client, cni gocni.CNI, resolver proxy.BaseURLResolver) func(w http.ResponseWriter, r *http.Request) {
 
 	return func(w http.ResponseWriter, r *http.Request) {
 
@@ -30,12 +34,9 @@ func MakeReplicaUpdateHandler(client *containerd.Client, cni gocni.CNI) func(w h
 		log.Printf("[Scale] request: %s\n", string(body))
 
 		req := types.ScaleServiceRequest{}
-		err := json.Unmarshal(body, &req)
-
-		if err != nil {
+		if err := json.Unmarshal(body, &req); err != nil {
 			log.Printf("[Scale] error parsing input: %s\n", err)
 			http.Error(w, err.Error(), http.StatusBadRequest)
-
 			return
 		}
 
@@ -55,18 +56,23 @@ func MakeReplicaUpdateHandler(client *containerd.Client, cni gocni.CNI) func(w h
 
 		name := req.ServiceName
 
-		if _, err := GetFunction(client, name, namespace); err != nil {
+		fn, err := GetFunction(client, name, namespace)
+		if err != nil {
 			msg := fmt.Sprintf("service %s not found", name)
 			log.Printf("[Scale] %s\n", msg)
 			http.Error(w, msg, http.StatusNotFound)
 			return
 		}
 
-		ctx := namespaces.WithNamespace(context.Background(), namespace)
+		healthPath := "/_/healthz"
+		if v := fn.annotations["com.openfaas.health.http.path"]; len(v) > 0 {
+			healthPath = v
+		}
 
-		ctr, ctrErr := client.LoadContainer(ctx, name)
-		if ctrErr != nil {
-			msg := fmt.Sprintf("cannot load service %s, error: %s", name, ctrErr)
+		ctx := namespaces.WithNamespace(context.Background(), namespace)
+		ctr, err := client.LoadContainer(ctx, name)
+		if err != nil {
+			msg := fmt.Sprintf("cannot load service %s, error: %s", name, err)
 			log.Printf("[Scale] %s\n", msg)
 			http.Error(w, msg, http.StatusNotFound)
 			return
@@ -75,16 +81,16 @@ func MakeReplicaUpdateHandler(client *containerd.Client, cni gocni.CNI) func(w h
 		var taskExists bool
 		var taskStatus *containerd.Status
 
-		task, taskErr := ctr.Task(ctx, nil)
-		if taskErr != nil {
-			msg := fmt.Sprintf("cannot load task for service %s, error: %s", name, taskErr)
+		task, err := ctr.Task(ctx, nil)
+		if err != nil {
+			msg := fmt.Sprintf("cannot load task for service %s, error: %s", name, err)
 			log.Printf("[Scale] %s\n", msg)
 			taskExists = false
 		} else {
 			taskExists = true
-			status, statusErr := task.Status(ctx)
-			if statusErr != nil {
-				msg := fmt.Sprintf("cannot load task status for %s, error: %s", name, statusErr)
+			status, err := task.Status(ctx)
+			if err != nil {
+				msg := fmt.Sprintf("cannot load task status for %s, error: %s", name, err)
 				log.Printf("[Scale] %s\n", msg)
 				http.Error(w, msg, http.StatusInternalServerError)
 				return
@@ -99,28 +105,31 @@ func MakeReplicaUpdateHandler(client *containerd.Client, cni gocni.CNI) func(w h
 		if req.Replicas == 0 {
 			// If a task is running, pause it
 			if taskExists && taskStatus.Status == containerd.Running {
-				if pauseErr := task.Pause(ctx); pauseErr != nil {
-					wrappedPauseErr := fmt.Errorf("error pausing task %s, error: %s", name, pauseErr)
-					log.Printf("[Scale] %s\n", wrappedPauseErr.Error())
-					http.Error(w, wrappedPauseErr.Error(), http.StatusNotFound)
+				if err := task.Pause(ctx); err != nil {
+					werr := fmt.Errorf("error pausing task %s, error: %s", name, err)
+					log.Printf("[Scale] %s\n", werr.Error())
+					http.Error(w, werr.Error(), http.StatusNotFound)
 					return
 				}
 			}
+
+			// Otherwise, no action is required
+			return
 		}
 
 		if taskExists {
 			if taskStatus != nil {
 				if taskStatus.Status == containerd.Paused {
-					if resumeErr := task.Resume(ctx); resumeErr != nil {
-						log.Printf("[Scale] error resuming task %s, error: %s\n", name, resumeErr)
-						http.Error(w, resumeErr.Error(), http.StatusBadRequest)
+					if err := task.Resume(ctx); err != nil {
+						log.Printf("[Scale] error resuming task %s, error: %s\n", name, err)
+						http.Error(w, err.Error(), http.StatusBadRequest)
 						return
 					}
 				} else if taskStatus.Status == containerd.Stopped {
 					// Stopped tasks cannot be restarted, must be removed, and created again
-					if _, delErr := task.Delete(ctx); delErr != nil {
-						log.Printf("[Scale] error deleting stopped task %s, error: %s\n", name, delErr)
-						http.Error(w, delErr.Error(), http.StatusBadRequest)
+					if _, err := task.Delete(ctx); err != nil {
+						log.Printf("[Scale] error deleting stopped task %s, error: %s\n", name, err)
+						http.Error(w, err.Error(), http.StatusBadRequest)
 						return
 					}
 					createNewTask = true
@@ -131,12 +140,70 @@ func MakeReplicaUpdateHandler(client *containerd.Client, cni gocni.CNI) func(w h
 		}
 
 		if createNewTask {
-			deployErr := createTask(ctx, client, ctr, cni)
-			if deployErr != nil {
-				log.Printf("[Scale] error deploying %s, error: %s\n", name, deployErr)
-				http.Error(w, deployErr.Error(), http.StatusBadRequest)
+			err := createTask(ctx, client, ctr, cni)
+			if err != nil {
+				log.Printf("[Scale] error deploying %s, error: %s\n", name, err)
+				http.Error(w, err.Error(), http.StatusBadRequest)
 				return
 			}
 		}
+
+		if err := waitUntilHealthy(name, resolver, healthPath); err != nil {
+			log.Printf("[Scale] error waiting for function %s to become ready, error: %s\n", name, err)
+			http.Error(w, err.Error(), http.StatusBadRequest)
+			return
+		}
 	}
 }
+
+// waitUntilHealthy blocks until the healthPath returns a HTTP 200 for the
+// IP address resolved for the given function.
+// Maximum retries: 100
+// Delay between each attempt: 20ms
+// A custom path can be set via an annotation in the function's spec:
+//  com.openfaas.health.http.path: /handlers/ready
+//
+func waitUntilHealthy(name string, resolver proxy.BaseURLResolver, healthPath string) error {
+	endpoint, err := resolver.Resolve(name)
+	if err != nil {
+		return err
+	}
+
+	host, port, _ := net.SplitHostPort(endpoint.Host)
+	u, err := url.Parse(fmt.Sprintf("http://%s:%s%s", host, port, healthPath))
+	if err != nil {
+		return err
+	}
+
+	// Try to hit the health endpoint and block until
+	// ready.
+	attempts := 100
+	pause := time.Millisecond * 20
+	for i := 0; i < attempts; i++ {
+		req, err := http.NewRequest(http.MethodGet, u.String(), nil)
+		if err != nil {
+			return err
+		}
+
+		res, err := http.DefaultClient.Do(req)
+		if err != nil {
+			return err
+		}
+
+		if res.Body != nil {
+			res.Body.Close()
+		}
+
+		if res.StatusCode != http.StatusOK {
+			return fmt.Errorf("unexpected health status: %d", res.StatusCode)
+		}
+
+		if err == nil {
+			break
+		}
+
+		time.Sleep(pause)
+	}
+
+	return nil
+}