Initial merge of faas-containerd

This patch completes part of the work in #20 by porting the code
for faas-containerd in-tree. When tested, I was able to deploy
and then remove figlet from the store on `x86_64`.

In a follow-up PR, duplication will be removed where possible
and consolidated with updated documentation.

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

pkg/provider/handlers/scale.go

@@ -0,0 +1,102 @@
+package handlers
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"io/ioutil"
+	"log"
+	"net/http"
+
+	"github.com/containerd/containerd"
+	"github.com/containerd/containerd/namespaces"
+	gocni "github.com/containerd/go-cni"
+	"github.com/openfaas/faas-provider/types"
+)
+
+func MakeReplicaUpdateHandler(client *containerd.Client, cni gocni.CNI) func(w http.ResponseWriter, r *http.Request) {
+
+	return func(w http.ResponseWriter, r *http.Request) {
+
+		if r.Body == nil {
+			http.Error(w, "expected a body", http.StatusBadRequest)
+			return
+		}
+
+		defer r.Body.Close()
+
+		body, _ := ioutil.ReadAll(r.Body)
+		log.Printf("[Scale] request: %s\n", string(body))
+
+		req := types.ScaleServiceRequest{}
+		err := json.Unmarshal(body, &req)
+
+		if err != nil {
+			log.Printf("[Scale] error parsing input: %s\n", err)
+			http.Error(w, err.Error(), http.StatusBadRequest)
+
+			return
+		}
+
+		name := req.ServiceName
+
+		if _, err := GetFunction(client, name); 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(), FunctionNamespace)
+
+		ctr, ctrErr := client.LoadContainer(ctx, name)
+		if ctrErr != nil {
+			msg := fmt.Sprintf("cannot load service %s, error: %s", name, ctrErr)
+			log.Printf("[Scale] %s\n", msg)
+			http.Error(w, msg, http.StatusNotFound)
+			return
+		}
+
+		taskExists := true
+		task, taskErr := ctr.Task(ctx, nil)
+		if taskErr != nil {
+			msg := fmt.Sprintf("cannot load task for service %s, error: %s", name, taskErr)
+			log.Printf("[Scale] %s\n", msg)
+			taskExists = false
+		}
+
+		if req.Replicas > 0 {
+			if taskExists {
+				if status, statusErr := task.Status(ctx); statusErr == nil {
+					if status.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)
+						}
+					}
+				}
+			} else {
+				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)
+					return
+				}
+				return
+			}
+		} else {
+			if taskExists {
+				if status, statusErr := task.Status(ctx); statusErr == nil {
+					if status.Status == containerd.Running {
+						if pauseErr := task.Pause(ctx); pauseErr != nil {
+							log.Printf("[Scale] error pausing task %s, error: %s\n", name, pauseErr)
+							http.Error(w, pauseErr.Error(), http.StatusBadRequest)
+						}
+					}
+				}
+			}
+		}
+
+	}
+
+}