Is a connection to MongoDB automatically closed on process.exit()?

Question

I am using the mongodb driver to connect to a MongoDB server from a Node.js application.

Supposed my application crashes, or I call process.exit(), without closing the connection previously - does it stay open? Is it closed automatically? If so, who cares about that? Node.js? The TCP/IP stack? MongoDB? …? And: When does that happen?

Does it make a difference if I hit <Ctrl>+<C>?

Answer 1

The answer is no. DB connections don't gracefully shut down when you exit (or crash).

To do that you should use something similar to:

// Create a function to terminate your app gracefully:
function gracefulShutdown(){
    // First argument is [force], see mongoose doc.
    mongoose.connection.close(false, () => {
      console.log('MongoDb connection closed.');
    });
  });
}

// Ask node to run your function before exit:

// This will handle process.exit():
process.on('exit', gracefulShutdown);

// This will handle kill commands, such as CTRL+C:
process.on('SIGINT', gracefulShutdown);
process.on('SIGTERM', gracefulShutdown);
process.on('SIGKILL', gracefulShutdown);

// This will prevent dirty exit on code-fault crashes:
process.on('uncaughtException', gracefulShutdown);

There are also some packages to handle this behavior, but this is usually very straightforward, and simple to implement.