feat(core): pass signal when manually invoking close

[bartversluijs]

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PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Other... Please describe:

What is the current behavior?

At the moment, when manually invoking the app.close(), no signal can be passed to the shutdown hooks (beforeApplicationShutdown & onApplicationShutdown). This means creating custom graceful shutdown implementations are limited by the fact that something simple as a signal can't be used for handling shutdown features.

Issue Number: N/A

What is the new behavior?

By adding the possibility the pass a signal to the app.close() function, which is still not required, the signal can be used in shutdown hooks, even when custom graceful shutdown implementations are made. Although it's a small feature, it makes creating graceful shutdowns somewhat easier, even if it's for logging only for example.

Does this PR introduce a breaking change?

• Yes
• No

Other information

[coveralls]

Pull Request Test Coverage Report for Build 58763218-68d8-4232-9174-89e899e36f2f

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 93.404%

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Totals
Change from base Build 1506e0bc-b980-484c-bfc0-6bf793b389fb:	0.0%
Covered Lines:	6202
Relevant Lines:	6640

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💛 - Coveralls

[micalevisk]

can you please share a code snippet on how that would look like?

[bartversluijs]

Hereby a code snippet as requested for closing the NestJS application with a exit signal:

// Define the custom shutdown signals
const shutdownSignals: Array<NodeJS.Signals> = ['SIGTERM', 'SIGINT', 'SIGABRT'];]

// Listen to those signals
shutdownSignals.forEach((signal) => {
  process.on(signal, async (signal: NodeJS.Signals | undefined, code: number) => {
    // Invoke custom shutdown methods or handlers here, when creating a custom graceful shutdown
    await beforeWorkerShutdown(signal);

    // Then, manually close NestJS and passing the signal
    nestApplication.close(signal);

    // Next, invoke the custom 'onWorkerShutdown' handler.
    await onWorkerShutdown(signal);

    // Exit the process
    process.exit(code);
  });
});

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I currently have something like this in place with the cluster package of Node.js. When starting my application, it first creates some workers (web & background), but I have some worker-specific startup and shutdown handlers in place (e.g. a background worker should wait for all queue jobs to complete, but a web worker shouldn't listen to the queue in the first place). But at the moment, I can't pass the signal that is used for a shutdown to the NestJS shutdown handlers. Because it is just a small change and it can have a large benefit, I proposed this change.

[kamilmysliwiec]

lgtm