Add support for a default backend service

Author: itzg

.gitignore

@@ -1,4 +1,6 @@
 /vendor/
 
 /.idea/
-/*.iml
+/*.iml
+/mc-router.exe
+/mc-router

README.md

@@ -25,16 +25,24 @@ Flags:
   "backend": "HOST:PORT"
 }
 ```
-
+* `POST /defaultRoute`
+  Registers a default route to the given backend. JSON body is structured as:
+```json
+{
+  "backend": "HOST:PORT"
+}
+```
 * `DELETE /routes/{serverAddress}`
   Deletes an existing route for the given `serverAddress`
 
 ## Using kubernetes service auto-discovery
 
 When running `mc-router` as a kubernetes pod and you pass the `--in-kube-cluster` command-line argument, then
-it will automatically watch for any services annotated with `mc-router.itzg.me/externalServerName`. The value
-of the annotation will be registered as the external hostname Minecraft clients would used to connect to the
-routed service. The service's clusterIP and target port are used as the routed backend.
+it will automatically watch for any services annotated with 
+- `mc-router.itzg.me/externalServerName` : The value of the annotation will be registered as the external hostname Minecraft clients would used to connect to the
+   routed service. The service's clusterIP and target port are used as the routed backend.
+- `mc-router.itzg.me/defaultServer` : The service's clusterIP and target port are used as the default if
+  no other `externalServiceName` annotations applies.
 
 For example, start `mc-router`'s container spec with
 

docs/k8s-mc-with-default.yaml

@@ -0,0 +1,94 @@
+---
+apiVersion: v1
+kind: Service
+metadata:
+  name: mc-stable
+  annotations:
+    "mc-router.itzg.me/defaultServer": "mc.your.domain"
+spec:
+  ports:
+  - port: 25565
+  selector:
+    run: mc-stable
+---
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  labels:
+    run: mc-stable
+  name: mc-stable
+spec:
+  selector:
+    matchLabels:
+      run: mc-stable
+  template:
+    metadata:
+      labels:
+        run: mc-stable
+    spec:
+      securityContext:
+        runAsUser: 1000
+        fsGroup: 1000
+      containers:
+      - image: itzg/minecraft-server
+        name: mc-stable
+        env:
+        - name: EULA
+          value: "TRUE"
+        ports:
+        - containerPort: 25565
+        volumeMounts:
+        - name: data
+          mountPath: /data
+      volumes:
+      - name: data
+        persistentVolumeClaim:
+          claimName: mc-stable
+---
+apiVersion: v1
+kind: Service
+metadata:
+  name: mc-snapshot
+  annotations:
+    "mc-router.itzg.me/externalServerName": "snapshot.your.domain"
+spec:
+  ports:
+  - port: 25565
+  selector:
+    run: mc-snapshot
+---
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  labels:
+    run: mc-snapshot
+  name: mc-snapshot
+spec:
+  selector:
+    matchLabels:
+      run: mc-snapshot
+  template:
+    metadata:
+      labels:
+        run: mc-snapshot
+    spec:
+      securityContext:
+        runAsUser: 1000
+        fsGroup: 1000
+      containers:
+      - image: itzg/minecraft-server
+        name: mc-snapshot
+        env:
+        - name: EULA
+          value: "TRUE"
+        - name: VERSION
+          value: "SNAPSHOT"
+        ports:
+        - containerPort: 25565
+        volumeMounts:
+        - name: data
+          mountPath: /data
+      volumes:
+      - name: data
+        persistentVolumeClaim:
+          claimName: mc-snapshot

server/k8s.go

@@ -12,6 +12,11 @@ import (
 	"net"
 )
 
+const (
+	AnnotationExternalServerName = "mc-router.itzg.me/externalServerName"
+	AnnotationDefaultServer      = "mc-router.itzg.me/defaultServer"
+)
+
 type IK8sWatcher interface {
 	StartWithConfig(kubeConfigFile string) error
 	StartInCluster() error
@@ -65,15 +70,23 @@ func (w *k8sWatcherImpl) startWithLoadedConfig(config *rest.Config) error {
 				if routableService != nil {
 					logrus.WithField("routableService", routableService).Debug("ADD")
 
-					Routes.CreateMapping(routableService.externalServiceName, routableService.containerEndpoint)
+					if routableService.externalServiceName != "" {
+						Routes.CreateMapping(routableService.externalServiceName, routableService.containerEndpoint)
+					} else {
+						Routes.SetDefaultRoute(routableService.containerEndpoint)
+					}
 				}
 			},
 			DeleteFunc: func(obj interface{}) {
 				routableService := extractRoutableService(obj)
 				if routableService != nil {
 					logrus.WithField("routableService", routableService).Debug("DELETE")
 
-					Routes.DeleteMapping(routableService.externalServiceName)
+					if routableService.externalServiceName != "" {
+						Routes.DeleteMapping(routableService.externalServiceName)
+					} else {
+						Routes.SetDefaultRoute("")
+					}
 				}
 			},
 			UpdateFunc: func(oldObj, newObj interface{}) {
@@ -85,8 +98,12 @@ func (w *k8sWatcherImpl) startWithLoadedConfig(config *rest.Config) error {
 						"new": newRoutableService,
 					}).Debug("UPDATE")
 
-					Routes.DeleteMapping(oldRoutableService.externalServiceName)
-					Routes.CreateMapping(newRoutableService.externalServiceName, newRoutableService.containerEndpoint)
+					if oldRoutableService.externalServiceName != "" && newRoutableService.externalServiceName != "" {
+						Routes.DeleteMapping(oldRoutableService.externalServiceName)
+						Routes.CreateMapping(newRoutableService.externalServiceName, newRoutableService.containerEndpoint)
+					} else {
+						Routes.SetDefaultRoute(newRoutableService.containerEndpoint)
+					}
 				}
 			},
 		},
@@ -116,22 +133,28 @@ func extractRoutableService(obj interface{}) *routableService {
 		return nil
 	}
 
-	if externalServiceName, exists := service.Annotations["mc-router.itzg.me/externalServerName"]; exists {
-		clusterIp := service.Spec.ClusterIP
-		port := "25565"
-		for _, p := range service.Spec.Ports {
-			if p.Port == 25565 {
-				if p.TargetPort.String() != "" {
-					port = p.TargetPort.String()
-				}
-			}
-		}
-		rs := &routableService{
-			externalServiceName: externalServiceName,
-			containerEndpoint:   net.JoinHostPort(clusterIp, port),
-		}
-		return rs
+	if externalServiceName, exists := service.Annotations[AnnotationExternalServerName]; exists {
+		return buildDetails(service, externalServiceName)
+	} else if _, exists := service.Annotations[AnnotationDefaultServer]; exists {
+		return buildDetails(service, "")
 	}
 
 	return nil
 }
+
+func buildDetails(service *v1.Service, externalServiceName string) *routableService {
+	clusterIp := service.Spec.ClusterIP
+	port := "25565"
+	for _, p := range service.Spec.Ports {
+		if p.Port == 25565 {
+			if p.TargetPort.String() != "" {
+				port = p.TargetPort.String()
+			}
+		}
+	}
+	rs := &routableService{
+		externalServiceName: externalServiceName,
+		containerEndpoint:   net.JoinHostPort(clusterIp, port),
+	}
+	return rs
+}

server/routes.go

@@ -1,11 +1,11 @@
 package server
 
 import (
-	"sync"
-	"net/http"
 	"encoding/json"
-	"github.com/sirupsen/logrus"
 	"github.com/gorilla/mux"
+	"github.com/sirupsen/logrus"
+	"net/http"
+	"sync"
 )
 
 func init() {
@@ -15,6 +15,9 @@ func init() {
 	apiRoutes.Path("/routes").Methods("POST").
 		Headers("Content-Type", "application/json").
 		HandlerFunc(routesCreateHandler)
+	apiRoutes.Path("/defaultRoute").Methods("POST").
+		Headers("Content-Type", "application/json").
+		HandlerFunc(routesSetDefault)
 	apiRoutes.Path("/routes/{serverAddress}").Methods("DELETE").HandlerFunc(routesDeleteHandler)
 }
 
@@ -43,7 +46,7 @@ func routesDeleteHandler(writer http.ResponseWriter, request *http.Request) {
 func routesCreateHandler(writer http.ResponseWriter, request *http.Request) {
 	var definition = struct {
 		ServerAddress string
-		Backend string
+		Backend       string
 	}{}
 
 	defer request.Body.Close()
@@ -60,6 +63,25 @@ func routesCreateHandler(writer http.ResponseWriter, request *http.Request) {
 	writer.WriteHeader(http.StatusCreated)
 }
 
+func routesSetDefault(writer http.ResponseWriter, request *http.Request) {
+	var body = struct {
+		Backend string
+	}{}
+
+	defer request.Body.Close()
+
+	decoder := json.NewDecoder(request.Body)
+	err := decoder.Decode(&body)
+	if err != nil {
+		logrus.WithError(err).Error("Unable to parse request")
+		writer.WriteHeader(http.StatusBadRequest)
+		return
+	}
+
+	Routes.SetDefaultRoute(body.Backend)
+	writer.WriteHeader(http.StatusOK)
+}
+
 type IRoutes interface {
 	RegisterAll(mappings map[string]string)
 	// FindBackendForServerAddress returns the host:port for the external server address, if registered.
@@ -68,6 +90,7 @@ type IRoutes interface {
 	GetMappings() map[string]string
 	DeleteMapping(serverAddress string) bool
 	CreateMapping(serverAddress string, backend string)
+	SetDefaultRoute(backend string)
 }
 
 var Routes IRoutes = &routesImpl{}
@@ -81,17 +104,31 @@ func (r *routesImpl) RegisterAll(mappings map[string]string) {
 
 type routesImpl struct {
 	sync.RWMutex
-	mappings   map[string]string
+	mappings     map[string]string
+	defaultRoute string
+}
+
+func (r *routesImpl) SetDefaultRoute(backend string) {
+	r.defaultRoute = backend
+
+	logrus.WithFields(logrus.Fields{
+		"backend": backend,
+	}).Info("Using default route")
 }
 
 func (r *routesImpl) FindBackendForServerAddress(serverAddress string) string {
 	r.RLock()
 	defer r.RUnlock()
 
 	if r.mappings == nil {
-		return ""
+		return r.defaultRoute
 	} else {
-		return r.mappings[serverAddress]
+
+		if route, exists := r.mappings[serverAddress]; exists {
+			return route
+		} else {
+			return r.defaultRoute
+		}
 	}
 }
 
@@ -125,7 +162,7 @@ func (r *routesImpl) CreateMapping(serverAddress string, backend string) {
 
 	logrus.WithFields(logrus.Fields{
 		"serverAddress": serverAddress,
-		"backend": backend,
+		"backend":       backend,
 	}).Info("Creating route")
 	r.mappings[serverAddress] = backend
-}
+}