Executor abstraction (#384)

This change adds a layer of abstraction over poolmgr. Poolmgr is now just one of the ways to turn a function into a service; other implementations will be added. The executor abstraction is a uniform API over all these implementations.

* Executor layer added on top of pool manager

* Removed the external server for executor

* Minor changes to keep existing semantics as much possible

* Separating the executor vs. poolmgr backend functionality and associated data members

* Executor logic separated from Poolmgr backend completely, placeholder for new backend

* Changed references to poolmgr in tests

* Moved poolmgr to it's package, as a side effect moved Cache to its's package (was causing cyclical dependency) and had to make some data structures exposed outside package

* Rebased from master and changed references to tpr -> crd

* Executor layer added on top of pool manager

* Executor logic separated from Poolmgr backend completely, placeholder for new backend

* Changed podName to a generic objectReference in fscache (#391)

Changed podName to a generic objectReference in function service cache implementation.

* Moved poolmgr to it's package, as a side effect moved Cache to its's package (was causing cyclical dependency) and had to make some data structures exposed outside package

* Rebased from master and changed references to tpr -> crd

* Merged from master with latest changes

* Removed stale executor service & deployment from previous merge

* Addressed review comments, still testing some areas

router/functionHandler.go

@@ -28,18 +28,18 @@ import (
 	"github.com/gorilla/mux"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 
-	poolmgrClient "github.com/fission/fission/poolmgr/client"
+	executorClient "github.com/fission/fission/executor/client"
 )
 
 type functionHandler struct {
 	fmap     *functionServiceMap
-	poolmgr  *poolmgrClient.Client
+	executor *executorClient.Client
 	function *metav1.ObjectMeta
 }
 
 func (fh *functionHandler) getServiceForFunction() (*url.URL, error) {
-	// call poolmgr, get a url for a function
-	svcName, err := fh.poolmgr.GetServiceForFunction(fh.function)
+	// call executor, get a url for a function
+	svcName, err := fh.executor.GetServiceForFunction(fh.function)
 	if err != nil {
 		return nil, err
 	}
@@ -83,10 +83,10 @@ func (rrt RetryingRoundTripper) RoundTrip(req *http.Request) (*http.Response, er
 }
 
 func (fh *functionHandler) tapService(serviceUrl *url.URL) {
-	if fh.poolmgr == nil {
+	if fh.executor == nil {
 		return
 	}
-	fh.poolmgr.TapService(serviceUrl)
+	fh.executor.TapService(serviceUrl)
 }
 
 func (fh *functionHandler) handler(responseWriter http.ResponseWriter, request *http.Request) {
@@ -121,7 +121,7 @@ func (fh *functionHandler) handler(responseWriter http.ResponseWriter, request *
 		fh.fmap.assign(fh.function, serviceUrl)
 	} else {
 		// if we're using our cache, asynchronously tell
-		// poolmgr we're using this service
+		// executor we're using this service
 		go fh.tapService(serviceUrl)
 	}