shutdownmanager

ShutdownManager is a lightweight TypeScript library designed to manage the graceful shutdown of services in a Node.js application. It listens for OS signals (SIGINT, SIGTERM) and ensures that all registered services are properly closed before the application exits. This is especially useful for releasing database connections, closing file streams, or cleaning up resources to prevent data corruption and ensure a smooth restart.

Installation

You can install ShutdownManager using npm:

npm install shutdownmanager

Or, you can add it to your package.json file:

{
  "dependencies": {
    "shutdownmanager": "^1.0.0"
  }
}

And then run:

npm install

Usage

Basic Example

First, import the ShutdownManager:

import { ShutdownManager } from 'shutdownmanager';

Or in CommonJS syntax:

const { ShutdownManager } = require('shutdownmanager');

Next, initialize the ShutdownManager and add your services. Each service should have a close method which returns a Promise. This method will contain the logic to gracefully shut down the service.

const databaseService = {
  close: async (): Promise<void> => {
    console.log('Closing database connections...');
    // Add logic to close database connections here
  }
};

const eventBusService = {
  close: async (): Promise<void> => {
    console.log('Closing event bus connections...');
    // Add logic to close event bus connections here
  }
};

const shutdownManager = new ShutdownManager(databaseService, eventBusService);

Manually Initiating Shutdown

While shutdownmanager is designed to handle the graceful shutdown of services in response to OS signals like SIGINT and SIGTERM, you can also manually initiate the shutdown process using the shutdown method.

Waiting for Services to Close

To manually initiate the shutdown and wait for all services to close, call the shutdown method on the ShutdownManager instance. This method returns a Promise that resolves when all services have been successfully closed.

await shutdownManager.shutdown();

This can be particularly useful in scenarios where you need to programmatically control when the shutdown process begins, rather than waiting for an OS signal.

Waiting for Services to Close with a Timeout

You can also manually initiate the shutdown with a timeout, ensuring that the process does not hang indefinitely if there are issues closing the services. To do this, pass the desired timeout (in milliseconds) as an argument to the shutdown method. This method returns a Promise that resolves when all services have been closed, or rejects if the timeout is reached before the shutdown is complete.

await shutdownManager.shutdown(5000);

It’s important to note that even if you are using the shutdown method to manually initiate the shutdown process, shutdownmanager will still respond to OS signals. If a SIGINT or SIGTERM signal is received while the shutdown is in progress, it will not interrupt the manual shutdown process. However, if the shutdown is initiated by an OS signal and then shutdown is called manually, the method will return the Promise of the ongoing shutdown process, ensuring that your services are not closed multiple times.

By providing these manual controls in addition to automatic handling of OS signals, shutdownmanager offers a flexible solution for managing the graceful shutdown of services in various scenarios.

Wait for Manager to Close

If you want to wait for the shutdown manager to finish its shutdown process, you can use the wait method:

const shutdownManager = new ShutdownManager(/*...services...*/);
//...
await shutdownManager.wait();

Using a Custom Logger

To use a custom logger, pass it as the first argument to the ShutdownManager constructor. Ensure that your logger has info, debug, error, and warn methods.

const customLogger = {
  info: (message: string) => console.log(`INFO: ${message}`),
  debug: (message: string) => console.log(`DEBUG: ${message}`),
  error: (message: string, error?: Error) => console.error(`ERROR: ${message}`, error),
  warn: (message: string) => console.warn(`WARN: ${message}`)
};

const shutdownManager = new ShutdownManager(customLogger, databaseService, eventBusService);

This custom logger will be used for logging information, debug messages, errors, and warnings during the shutdown process.

Using NoOp Logger

If you don't want any logs to be printed, you can use the noOpLogger provided by the library:

import { noOpLogger } from 'shutdownmanager';

const shutdownManager = new ShutdownManager(noOpLogger, databaseService, eventBusService);

Alternatively, you can pass null as the first argument to use the noOpLogger:

const shutdownManager = new ShutdownManager(null, databaseService, eventBusService);

Triggering a Graceful Shutdown

You can trigger a graceful shutdown manually by sending a SIGINT or SIGTERM signal to your Node.js application.

kill -SIGINT <process_id>

Or, if you're running the application in a terminal, you can usually trigger a graceful shutdown with Ctrl+C.

Graceful Shutdown

shutdownmanager listens for SIGINT and SIGTERM signals, and it will call the close method on each service that has been added to it, allowing you to ensure that resources are properly closed before the application exits.

Your services should aim to handle these closures as gracefully as possible, ensuring that any in-flight operations are completed before shutting down.

License

ShutdownManager is MIT licensed. See LICENSE for details.