Shutting down cleanly

An application should finish the messages it has read from the queue, and read no more, before it exits. That happens when you press Ctrl+C, when a process manager sends a signal such as kill -INT 1234, or when the pod, container or host it runs on is stopping. This page covers what the bus does by default and how to take over shutdown yourself.

The default

A bus that handles messages listens for SIGINT and SIGTERM, and stops when it receives one: it stops reading from the queue and waits for the handlers that are running to finish. The process then exits once nothing else keeps it running, such as an open connection to the transport.

Disposing the bus yourself

To close the transport and persistence connections too, so the process exits, listen for the signals yourself and call bus.dispose(). Pass withInterruptSignals([]) so the bus doesn't also listen for them. Hosts that own shutdown, such as NestJS or AWS Lambda, need this too.

const bus = Bus.configure()
  .withMessageTypes(messageTypes)
  .withHandler(reserveRoomHandler)
  // Don't stop on signals, since the app handles them below
  .withInterruptSignals([])
  .build()

await bus.initialize()
await bus.start()

const shutDown = (signal: NodeJS.Signals) => {
  console.log(`Received ${signal}, shutting down...`)
  // Waits for the messages being handled, then disconnects from the transport
  // and persistence so the process can exit
  bus.dispose().catch(error => {
    console.error('Failed to shut down the bus', error)
    process.exitCode = 1
  })
}

process.once('SIGINT', shutDown)
process.once('SIGTERM', shutDown)

To stop on other signals as well, pass all the signals the bus should listen for. They replace the defaults:

// Also stop on SIGUSR2, as well as the default SIGINT and SIGTERM
Bus.configure().withInterruptSignals(['SIGINT', 'SIGTERM', 'SIGUSR2'])

Send-only buses never listen for signals.

See also

• Lifecycle hooks
• Long running processes, for work that takes longer than a shutdown can wait
• BusInstance in the API reference