From 6bc1220d8bacac1d2c15c9bee2e7ae13f3ca0d3a Mon Sep 17 00:00:00 2001
From: Gerardo Viedma <gviedma@users.noreply.github.com>
Date: Thu, 15 Mar 2018 10:28:56 +0000
Subject: [PATCH] Adds extension points for runner pools in load-balanced mode
 (Patch 1/2) (#851)

* adds extension points for runner pools in load-balanced mode

* adds error to return values in RunnerPool and Runner interfaces
---
 api/models/runner_pool.go | 31 +++++++++++++++++++++++++++++++
 api/server/server.go      |  7 +++++++
 fnext/setup.go            |  3 +++
 3 files changed, 41 insertions(+)
 create mode 100644 api/models/runner_pool.go

diff --git a/api/models/runner_pool.go b/api/models/runner_pool.go
new file mode 100644
index 000000000..bcb3dfd26
--- /dev/null
+++ b/api/models/runner_pool.go
@@ -0,0 +1,31 @@
+package models
+
+import (
+	"context"
+	"io"
+	"net/http"
+	"time"
+)
+
+// RunnerPool is the abstraction for getting an ordered list of runners to try for a call
+type RunnerPool interface {
+	Runners(call RunnerCall) ([]Runner, error)
+	Shutdown() error
+}
+
+// Runner is the interface to invoke the execution of a function call on a specific runner
+type Runner interface {
+	TryExec(ctx context.Context, call RunnerCall) (bool, error)
+	Close() error
+	Address() string
+}
+
+// RunnerCall provides access to the necessary details of request in order for it to be
+// processed by a RunnerPool
+type RunnerCall interface {
+	SlotDeadline() time.Time
+	Request() *http.Request
+	ResponseWriter() io.Writer
+	StdErr() io.ReadWriteCloser
+	Model() *Call
+}
diff --git a/api/server/server.go b/api/server/server.go
index 45e8a6cf2..bd54d3481 100644
--- a/api/server/server.go
+++ b/api/server/server.go
@@ -113,6 +113,7 @@ type Server struct {
 	rootMiddlewares []fnext.Middleware
 	apiMiddlewares  []fnext.Middleware
 	promExporter    *prometheus.Exporter
+	runnerPool      models.RunnerPool
 	// Extensions can append to this list of contexts so that cancellations are properly handled.
 	extraCtxs []context.Context
 }
@@ -842,6 +843,12 @@ func (s *Server) Datastore() models.Datastore {
 	return s.datastore
 }
 
+// WithRunnerPool provides an extension point for overriding
+// the default runner pool implementation when running in load-balanced mode
+func (s *Server) WithRunnerPool(runnerPool models.RunnerPool) {
+	s.runnerPool = runnerPool
+}
+
 // returns the unescaped ?cursor and ?perPage values
 // pageParams clamps 0 < ?perPage <= 100 and defaults to 30 if 0
 // ignores parsing errors and falls back to defaults.
diff --git a/fnext/setup.go b/fnext/setup.go
index 536cc3e71..99f23ae23 100644
--- a/fnext/setup.go
+++ b/fnext/setup.go
@@ -38,6 +38,9 @@ type ExtServer interface {
 	// AddRouteEndpoint adds an endpoints to /v1/apps/:app/routes/:route/x
 	AddRouteEndpointFunc(method, path string, handler func(w http.ResponseWriter, r *http.Request, app *models.App, route *models.Route))
 
+	// WithRunnerPool overrides the default runner pool implementation when running in load-balanced mode
+	WithRunnerPool(runnerPool models.RunnerPool)
+
 	// Datastore returns the Datastore Fn is using
 	Datastore() models.Datastore
 }