What happens to active requests when Nginx reloads?

Question

IT Interview Practice · Accepted Answer

A graceful reload lets new workers use the new configuration while old workers finish their current work. It aims to apply changes without abruptly stopping active requests.

## Follow an in-progress download

Suppose a download is running when you reload. New workers start accepting new connections. The old worker can keep serving the existing download until it completes, then exit when its remaining work is finished.

For a typical installation, validate and reload with:

```sh
nginx -t && nginx -s reload
```

The first command checks configuration; the second requests reload only if the check succeeds. Use the correct configuration path and privileges for your installation. If applying the new configuration fails, the master keeps the previous configuration running.

## Long connections change the tradeoff

A WebSocket can keep an old worker alive much longer. `worker_shutdown_timeout` can bound the shutdown wait, but connections may be closed when that limit is reached. Choose the bound according to whether clients can safely reconnect or resume work.

Test a reload during a download and a WebSocket session. Check worker lifetimes, errors and client recovery. A passed syntax check alone does not prove that the new backend routing works.

[Official documentation](https://nginx.org/en/docs/control.html).

Follow an in-progress download

Long connections change the tradeoff

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