feat(backend): add custom healthcheck package

apps/backend/README.md

@@ -20,5 +20,8 @@ npm run test
 - Pretty logs in development with [pino-pretty](https://npm.im/pino-pretty).
 - Graceful shutdown on exit signals via
   [close-with-grace](https://npm.im/close-with-grace).
+- Health checks via
+  [fastify-custom-healthcheck](https://npm.im/fastify-custom-healthcheck) allowing other
+  plugins to add custom health checks.
 - Basic multipart form handling via
   [@fastify/multipart](https://npm.im/@fastify/multipart).

apps/backend/app.ts

@@ -1,23 +1,15 @@
 import { Multipart } from "@fastify/multipart";
-import fastify, { FastifyRequest } from "fastify";
+import fastify, { FastifyBaseLogger, FastifyHttpOptions, FastifyRequest } from "fastify";
+import * as http from "node:http";
 import { basePlugin } from "./plugins/base.js";
 
-export async function buildApp() {
-	const loggerConfig =
-		process.env.NODE_ENV === "development" ?
-			{
-				transport: {
-					target: "pino-pretty",
-					options: {
-						ignore: "pid,hostname",
-					},
-				},
-			}
-		:	true;
-
-	const app = fastify({
-		logger: loggerConfig,
-	});
+export async function buildApp(opts: FastifyHttpOptions<http.Server> = {}) {
+	const app = fastify<
+		http.Server,
+		http.IncomingMessage,
+		http.ServerResponse,
+		FastifyBaseLogger
+	>(opts);
 
 	app.register(basePlugin);
 

apps/backend/package.json

@@ -14,6 +14,7 @@
     "close-with-grace": "^1.2.0",
     "dotenv": "^16.4.4",
     "fastify": "^4.26.0",
+    "fastify-custom-healthcheck": "^3.1.0",
     "fastify-plugin": "^4.5.1",
     "@fastify/multipart": "^8.1.0"
   },

apps/backend/plugins/base.test.ts

@@ -25,7 +25,6 @@ test("base", async (t) => {
 		});
 
 		const data = await response.json();
-		console.log(data);
 
 		assert.equal(response.status, 200);
 		assert.deepEqual(data, [
@@ -39,4 +38,27 @@ test("base", async (t) => {
 			},
 		]);
 	});
+
+	await t.test("health check", async (t) => {
+		await t.test("success", async (t) => {
+			const response = await app.inject({
+				method: "get",
+				path: "/health",
+			});
+
+			assert.equal(response.statusCode, 200);
+			assert.equal(response.json().healthChecks.label, "HEALTHY");
+		});
+
+		await t.test("fail", async (t) => {
+			app.addHealthCheck("label2", () => false, { value: true });
+			const response = await app.inject({
+				method: "get",
+				path: "/health",
+			});
+
+			assert.equal(response.statusCode, 500);
+			assert.equal(response.json().healthChecks.label2, "FAIL");
+		});
+	});
 });

apps/backend/plugins/base.ts

@@ -1,9 +1,11 @@
-import { FastifyInstance, FastifyRegisterOptions, RegisterOptions } from "fastify";
-import fp from "fastify-plugin";
 import fastifyMultipart, { FastifyMultipartBaseOptions } from "@fastify/multipart";
+import { RegisterOptions } from "fastify";
+import fastifyCustomHealthCheck from "fastify-custom-healthcheck";
+import fp from "fastify-plugin";
+import { FastifyBase } from "../types.js";
 
 async function base(
-	fastify: FastifyInstance,
+	fastify: FastifyBase,
 	options: RegisterOptions & {
 		multipart?: FastifyMultipartBaseOptions;
 	},
@@ -41,6 +43,20 @@ async function base(
 
 		...options.multipart,
 	});
+
+	// TODO: Why do we need `as any` here?
+	fastify.register(fastifyCustomHealthCheck as any, {
+		// TODO: we should allow configuring one or multiple routes
+
+		path: "/health",
+		info: {},
+	});
+
+	fastify.ready(() => {
+		fastify.addHealthCheck("label", () => true, {
+			value: true,
+		});
+	});
 }
 
 export const basePlugin = fp(base, {

apps/backend/server.ts

@@ -4,7 +4,21 @@ import dotenv from "dotenv";
 
 dotenv.config({ path: [".env.local", ".env"] });
 
-const app = await buildApp();
+const loggerConfig =
+	process.env.NODE_ENV === "development" ?
+		{
+			transport: {
+				target: "pino-pretty",
+				options: {
+					ignore: "pid,hostname",
+				},
+			},
+		}
+	:	true;
+
+const app = await buildApp({
+	logger: loggerConfig,
+});
 
 const closeGracefully = closeWithGrace({ delay: 500 }, async (options) => {
 	if (options.err) {

apps/backend/types.ts

@@ -0,0 +1,9 @@
+import type { FastifyBaseLogger, FastifyInstance } from "fastify";
+import http from "node:http";
+
+export type FastifyBase = FastifyInstance<
+	http.Server,
+	http.IncomingMessage,
+	http.ServerResponse,
+	FastifyBaseLogger
+>;