Pool Manager -- manage generic containers and their specialization

GenericPool is a pool of generic containers for an environment.
GenericPoolManager keeps track of all GenericPools, creating them
on-demand.

The pool manager API is simply a "lookup" for the service URL of a
function.  If one exists it is returned immediately; otherwise, a
generic pool is created, and then a pod is specialized from that pool.

poolmgr is designed to run from within the cluster, since it connects
to pod IP addresses directly.

This is a first cut with many pieces missing.

TODO:
* Use versioned kubernetes clients instead of the unversioned one
* Unit tests for GenericPoolMgr; improve unit test for GenericPool;
  test for API.
* Handle cases where a service exists but pod backing it has failed.
* On start up, use existing deployments/pods/services if they exist;
  in other words don't orphan resources on restart.
* Kill idle resources (services, pods, even generic pools)
* Autoscale generic pool (for example, by watching num ready pods)

poolmgr/gpm.go

@@ -0,0 +1,77 @@
+/*
+Copyright 2016 The Fission Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package poolmgr
+
+import (
+	"github.com/platform9/fission"
+	clientUnversioned "k8s.io/kubernetes/pkg/client/unversioned"
+)
+
+type (
+	GenericPoolManager struct {
+		pools            map[fission.Environment]*GenericPool
+		kubernetesClient *clientUnversioned.Client
+		namespace        string
+
+		requestChannel chan *request
+	}
+	request struct {
+		env             *fission.Environment
+		responseChannel chan *response
+	}
+	response struct {
+		error
+		pool *GenericPool
+	}
+)
+
+func MakeGenericPoolManager(client *clientUnversioned.Client, namespace string) *GenericPoolManager {
+	gpm := &GenericPoolManager{
+		pools:            make(map[fission.Environment]*GenericPool),
+		kubernetesClient: client,
+		namespace:        namespace,
+		requestChannel:   make(chan *request),
+	}
+	go gpm.service()
+	return gpm
+}
+
+func (gpm *GenericPoolManager) service() {
+	for {
+		select {
+		case req := <-gpm.requestChannel:
+			pool, ok := gpm.pools[*req.env]
+			if !ok {
+				pool, err := MakeGenericPool(gpm.kubernetesClient, req.env, 3, gpm.namespace)
+				if err != nil {
+					req.responseChannel <- &response{error: err}
+					continue
+				}
+				gpm.pools[*req.env] = pool
+				req.responseChannel <- &response{pool: pool}
+			}
+			req.responseChannel <- &response{pool: pool}
+		}
+	}
+}
+
+func (gpm *GenericPoolManager) GetPool(env *fission.Environment) (*GenericPool, error) {
+	c := make(chan *response)
+	gpm.requestChannel <- &request{env: env, responseChannel: c}
+	resp := <-c
+	return resp.pool, resp.error
+}