MongoDB "MongoTopologyClosedError: Topology is closed" in CI

The driver tried to use a client whose topology was already closed. In CI this usually means the client was disconnected (often in a test teardown) before a lingering async operation ran, or the connection dropped mid-run.

What this error means

A query fails with "MongoTopologyClosedError: Topology is closed" (older drivers: "Topology was destroyed"), frequently near the end of a test file after close() was called.

node

MongoTopologyClosedError: Topology is closed
    at ClientSession.startTransaction (.../mongodb/lib/sessions.js:200:23)

Common causes

The client was closed while work was still pending

An afterAll/teardown called client.close() before an un-awaited query or a background operation completed.

The connection dropped during the run

The mongod service was torn down or the network blipped, closing the topology while the app still held the client.

How to fix it

Await all work before closing the client

Ensure every query is awaited before teardown.
Close the client only in a single afterAll, after all tests finish.
Do not share one client across suites that close independently.

test-setup.js

afterAll(async () => {
  await client.close();
});

Keep the service alive for the whole job

Make sure the mongo service is not stopped until all steps that use it have completed.

How to prevent it

Await pending operations before closing the client.
Own client lifecycle in one place per test run.
Keep the mongod service up for the duration of DB steps.