MongoDB Atlas: connect the Node.js driver with one shared MongoClient

TL;DR: The Node.js driver wants one MongoClient per app, created once and reused. This skill covers the Atlas SRV string, the pool options that matter, and the per-request client trap that exhausts connections. Never hardcode it, never log it. - serverSelectionTimeoutMS: 5000 turns a hung connect into a fast, debuggable error instead of a 30s stall. - maxPoolSize caps connections per client. Verify Run the startup ping from the same network your app runs on.

The fix

1. Put the Atlas SRV string (mongodb+srv://...) in an env var. Never hardcode it, never log it.
2. serverSelectionTimeoutMS: 5000 turns a hung connect into a fast, debuggable error instead of a 30s stall.
3. maxPoolSize caps connections per client. 10 to 50 covers most apps; one client means one pool.
4. The driver connects lazily, so an explicit await client.connect() plus a ping at startup proves the string, user, password, and IP access list entry all work before traffic arrives.
5. Close with await client.close() only on process shutdown, never after a request.

When to use this

• This covers exactly what the title says: MongoDB Atlas.
• You are setting this up for the first time, or auditing an existing setup.
• You want the key gotchas in one place before you start.

When not to use this

• You are doing a different workflow with MongoDB; these steps are specific to the title above.
• You need the full reference docs; this is the short path, not the manual.

Compatibility

• Not pinned to a specific version; follows current MongoDB behavior.

Verified against current MongoDB docs 2026-09-26: the connection string format reference (mongodb+srv vs mongodb, option names like maxPoolSize and serverSelectionTimeoutMS) at https://www.mongodb.com/docs/manual/reference/connection-string/ and the Atlas connection troubleshooting guide at https://www.mongodb.com/docs/atlas/troubleshoot-connection/, which lists the IP access list, database user credentials, and connection string as the three things to check first.