Add support for a default backend service

.gitignore

@@ -2,3 +2,5 @@
 
 /.idea/
 /*.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
+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
@@ -65,7 +70,11 @@ func (w *k8sWatcherImpl) startWithLoadedConfig(config *rest.Config) error {
 				if routableService != nil {
 					logrus.WithField("routableService", routableService).Debug("ADD")
 
+					if routableService.externalServiceName != "" {
 						Routes.CreateMapping(routableService.externalServiceName, routableService.containerEndpoint)
+					} else {
+						Routes.SetDefaultRoute(routableService.containerEndpoint)
+					}
 				}
 			},
 			DeleteFunc: func(obj interface{}) {
@@ -73,7 +82,11 @@ func (w *k8sWatcherImpl) startWithLoadedConfig(config *rest.Config) error {
 				if routableService != nil {
 					logrus.WithField("routableService", routableService).Debug("DELETE")
 
+					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")
 
+					if oldRoutableService.externalServiceName != "" && newRoutableService.externalServiceName != "" {
 						Routes.DeleteMapping(oldRoutableService.externalServiceName)
 						Routes.CreateMapping(newRoutableService.externalServiceName, newRoutableService.containerEndpoint)
+					} else {
+						Routes.SetDefaultRoute(newRoutableService.containerEndpoint)
+					}
 				}
 			},
 		},
@@ -116,7 +133,16 @@ func extractRoutableService(obj interface{}) *routableService {
 		return nil
 	}
 
-	if externalServiceName, exists := service.Annotations["mc-router.itzg.me/externalServerName"]; exists {
+	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 {
@@ -132,6 +158,3 @@ func extractRoutableService(obj interface{}) *routableService {
 	}
 	return rs
 }
-
-	return nil
-}

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)
 }
 
@@ -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{}
@@ -82,6 +105,15 @@ func (r *routesImpl) RegisterAll(mappings map[string]string) {
 type routesImpl struct {
 	sync.RWMutex
 	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 {
@@ -89,9 +121,14 @@ func (r *routesImpl) FindBackendForServerAddress(serverAddress string) string {
 	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
+		}
 	}
 }