feat(backend): add /healthz endpoint (#13834)

* feat(backend): add /healthz endpoint

* feat(backend): also check meilisearch status if available

* style: header

* chore: no-store

* chore: healthcheck.sh

* style: format

packages/backend/src/server/HealthServerService.ts

@@ -0,0 +1,54 @@
+/*
+ * SPDX-FileCopyrightText: syuilo and misskey-project
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import { Inject, Injectable } from '@nestjs/common';
+import * as Redis from 'ioredis';
+import { DataSource } from 'typeorm';
+import { bindThis } from '@/decorators.js';
+import { DI } from '@/di-symbols.js';
+import { readyRef } from '@/boot/ready.js';
+import type { FastifyInstance, FastifyPluginOptions } from 'fastify';
+import type { MeiliSearch } from 'meilisearch';
+
+@Injectable()
+export class HealthServerService {
+	constructor(
+		@Inject(DI.redis)
+		private redis: Redis.Redis,
+
+		@Inject(DI.redisForPub)
+		private redisForPub: Redis.Redis,
+
+		@Inject(DI.redisForSub)
+		private redisForSub: Redis.Redis,
+
+		@Inject(DI.redisForTimelines)
+		private redisForTimelines: Redis.Redis,
+
+		@Inject(DI.db)
+		private db: DataSource,
+
+		@Inject(DI.meilisearch)
+		private meilisearch: MeiliSearch | null,
+	) {}
+
+	@bindThis
+	public createServer(fastify: FastifyInstance, options: FastifyPluginOptions, done: (err?: Error) => void) {
+		fastify.get('/', async (request, reply) => {
+			reply.code(await Promise.all([
+				new Promise<void>((resolve, reject) => readyRef.value ? resolve() : reject()),
+				this.redis.ping(),
+				this.redisForPub.ping(),
+				this.redisForSub.ping(),
+				this.redisForTimelines.ping(),
+				this.db.query('SELECT 1'),
+				...(this.meilisearch ? [this.meilisearch.health()] : []),
+			]).then(() => 200, () => 503));
+			reply.header('Cache-Control', 'no-store');
+		});
+
+		done();
+	}
+}