`onClose hook`

Runs when the server is closing, allowing plugins to release resources.

Since Fastify 5 Spec ↗

Syntax

app.addHook('onClose', async (instance) => {})

Parameters

Name	Type	Required	Description
`instance`	`FastifyInstance`	No	The instance being closed.

Returns

void | Promise<void> — Awaited during shutdown.

Examples

import Fastify from 'fastify';

const app = Fastify();
const pool = createPool();

app.addHook('onClose', async () => {
  await pool.end();
});

Notes

Triggered by app.close(). Use it to close database pools, flush buffers, and clear timers for graceful shutdown. Plugins typically register their own onClose to clean up encapsulated resources.