Clean up/make consistent the APIs for registering core components, make Docker an optional component at compile time (#1111)

api/agent/agent.go

@@ -12,7 +12,6 @@ import (
 	"time"
 
 	"github.com/fnproject/fn/api/agent/drivers"
-	"github.com/fnproject/fn/api/agent/drivers/docker"
 	"github.com/fnproject/fn/api/agent/protocol"
 	"github.com/fnproject/fn/api/common"
 	"github.com/fnproject/fn/api/id"
@@ -142,7 +141,11 @@ func New(da CallHandler, options ...AgentOption) Agent {
 	logrus.Infof("agent starting cfg=%+v", a.cfg)
 
 	if a.driver == nil {
-		a.driver = NewDockerDriver(&a.cfg)
+		d, err := NewDockerDriver(&a.cfg)
+		if err != nil {
+			logrus.WithError(err).Fatal("failed to create docker driver ")
+		}
+		a.driver = d
 	}
 
 	a.resources = NewResourceTracker(&a.cfg)
@@ -201,8 +204,8 @@ func WithCallOverrider(fn CallOverrider) AgentOption {
 }
 
 // NewDockerDriver creates a default docker driver from agent config
-func NewDockerDriver(cfg *AgentConfig) *docker.DockerDriver {
-	return docker.NewDocker(drivers.Config{
+func NewDockerDriver(cfg *AgentConfig) (drivers.Driver, error) {
+	return drivers.New("docker", drivers.Config{
 		DockerNetworks:       cfg.DockerNetworks,
 		ServerVersion:        cfg.MinDockerVersion,
 		PreForkPoolSize:      cfg.PreForkPoolSize,

api/agent/agent_test.go

@@ -16,6 +16,7 @@ import (
 	"testing"
 	"time"
 
+	_ "github.com/fnproject/fn/api/agent/drivers/docker"
 	"github.com/fnproject/fn/api/id"
 	"github.com/fnproject/fn/api/logs"
 	"github.com/fnproject/fn/api/models"

api/agent/drivers/docker/docker.go

@@ -646,3 +646,9 @@ func (w *waitResult) wait(ctx context.Context) (status string, err error) {
 }
 
 var _ drivers.Driver = &DockerDriver{}
+
+func init() {
+	drivers.Register("docker", func(config drivers.Config) (drivers.Driver, error) {
+		return NewDocker(config), nil
+	})
+}

api/agent/drivers/register.go

@@ -0,0 +1,26 @@
+package drivers
+
+import (
+	"fmt"
+	"github.com/sirupsen/logrus"
+)
+
+type DriverFunc func(config Config) (Driver, error)
+
+var drivers = make(map[string]DriverFunc)
+
+// Register adds  a container driver by name to this process
+func Register(name string, driverFunc DriverFunc) {
+	logrus.Infof("Registering container driver '%s'", name)
+	drivers[name] = driverFunc
+}
+
+// New Instantiates a driver by name
+func New(driverName string, config Config) (Driver, error) {
+	driverFunc, ok := drivers[driverName]
+
+	if !ok {
+		return nil, fmt.Errorf("agent driver \"%s\" is not registered", driverName)
+	}
+	return driverFunc(config)
+}