Use maintenance component to throw 503s when some components are unavailable

src/Application.ts

@@ -214,11 +214,6 @@ export default abstract class Application implements Extendable<ApplicationCompo
             });
         });
 
-        // Start components
-        for (const component of this.components) {
-            await component.start?.(app);
-        }
-
         // Components routes
         for (const component of this.components) {
             if (component.initRoutes) {
@@ -234,6 +229,11 @@ export default abstract class Application implements Extendable<ApplicationCompo
             component.setCurrentRouter(null);
         }
 
+        // Start components
+        for (const component of this.components) {
+            await component.start?.(app);
+        }
+
         // Routes
         this.routes(initRouter, handleRouter);
 
@@ -373,6 +373,10 @@ export default abstract class Application implements Extendable<ApplicationCompo
         return this.cacheProvider || null;
     }
 
+    public getComponents(): ApplicationComponent[] {
+        return [...this.components];
+    }
+
     public as<C extends ApplicationComponent | WebSocketListener<Application>>(type: Type<C>): C {
         const module = this.components.find(component => component.constructor === type) ||
             Object.values(this.webSocketListeners).find(listener => listener.constructor === type);

src/ApplicationComponent.ts

@@ -15,14 +15,18 @@ export default abstract class ApplicationComponent {
 
     public async init?(): Promise<void>;
 
-    public async start?(expressApp: Express): Promise<void>;
-
     public async initRoutes?(router: Router): Promise<void>;
 
     public async handleRoutes?(router: Router): Promise<void>;
 
+    public async start?(expressApp: Express): Promise<void>;
+
     public async stop?(): Promise<void>;
 
+    public isReady(): boolean {
+        return true;
+    }
+
     protected async prepare(name: string, prepare: () => Promise<void>): Promise<void> {
         let err;
         do {

src/TestApp.ts

@@ -21,6 +21,7 @@ import FormHelperComponent from "./components/FormHelperComponent.js";
 import FrontendToolsComponent from "./components/FrontendToolsComponent.js";
 import LogRequestsComponent from "./components/LogRequestsComponent.js";
 import MailComponent from "./components/MailComponent.js";
+import MaintenanceComponent from "./components/MaintenanceComponent.js";
 import MysqlComponent from "./components/MysqlComponent.js";
 import PreviousUrlComponent from "./components/PreviousUrlComponent.js";
 import RedisComponent from "./components/RedisComponent.js";
@@ -79,6 +80,9 @@ export default class TestApp extends Application {
         // Static files
         this.use(new ServeStaticDirectoryComponent('public'));
 
+        // Maintenance
+        this.use(new MaintenanceComponent());
+
         // Dynamic views and routes
         const intermediateDirectory = 'build';
         this.use(new FrontendToolsComponent(

src/components/MaintenanceComponent.ts

@@ -1,36 +1,29 @@
 import config from "config";
 import {NextFunction, Request, Response, Router} from "express";
 
-import Application from "../Application.js";
 import ApplicationComponent from "../ApplicationComponent.js";
 import {ServiceUnavailableHttpError} from "../HttpError.js";
 
 export default class MaintenanceComponent extends ApplicationComponent {
-    private readonly application: Application;
+    public async initRoutes(router: Router): Promise<void> {
-    private readonly canServe: () => boolean;
-
-    public constructor(application: Application, canServe: () => boolean) {
-        super();
-        this.application = application;
-        this.canServe = canServe;
-    }
-
-    public async handleRoutes(router: Router): Promise<void> {
         router.use((req: Request, res: Response, next: NextFunction) => {
             if (res.headersSent) {
                 return next();
             }
 
-            if (!this.application.isReady()) {
+            if (!this.getApp().isReady()) {
                 res.header({'Retry-After': 60});
                 res.locals.refresh_after = 5;
                 throw new ServiceUnavailableHttpError(`${config.get('app.name')} is readying up. Please wait a few seconds...`);
             }
 
-            if (!this.canServe()) {
+            for (const component of this.getApp().getComponents()) {
+                if (!component.isReady()) {
+                    res.header({'Retry-After': 60});
                     res.locals.refresh_after = 30;
                     throw new ServiceUnavailableHttpError(`${config.get('app.name')} is unavailable due to failure of dependent services.`);
                 }
+            }
 
             next();
         });

src/components/MysqlComponent.ts

@@ -12,7 +12,7 @@ export default class MysqlComponent extends ApplicationComponent {
         await MysqlConnectionManager.endPool();
     }
 
-    public canServe(): boolean {
+    public isReady(): boolean {
         return MysqlConnectionManager.isReady();
     }
 

src/components/RedisComponent.ts

@@ -9,7 +9,7 @@ import {logger} from "../Logger.js";
 
 export default class RedisComponent extends ApplicationComponent implements CacheProvider {
     private redisClient?: RedisClient;
-    private store?: Store;
+    private store: Store = new RedisStore(this);
 
     public async start(_app: Express): Promise<void> {
         this.redisClient = redis.createClient(config.get('redis.port'), config.get('redis.host'), {
@@ -18,8 +18,6 @@ export default class RedisComponent extends ApplicationComponent implements Cach
         this.redisClient.on('error', (err: Error) => {
             logger.error(err, 'An error occurred with redis.');
         });
-
-        this.store = new RedisStore(this);
     }
 
     public async stop(): Promise<void> {
@@ -30,11 +28,10 @@ export default class RedisComponent extends ApplicationComponent implements Cach
     }
 
     public getStore(): Store {
-        if (!this.store) throw `Redis store was not initialized.`;
         return this.store;
     }
 
-    public canServe(): boolean {
+    public isReady(): boolean {
         return this.redisClient !== undefined && this.redisClient.connected;
     }