**TL;DR:** The Connections metric jumps and the app starts failing. Find whether it is genuine load, a leak, or idle buildup, then act on the right cause. Flat means demand exceeds pool; climbing means clients are created and never closed. Check currentOp for sessions idle for a long time: idle app servers holding pools open, forgotten mongosh sessions, or tools left connected.

## The error

```text
Atlas Metrics shows Connections climbing; new operations start timing out.
```

## The fix

1. Is it flat at the cap (exhaustion) or climbing without bound (leak)? Flat means demand exceeds pool; climbing means clients are created and never closed.

2. Check currentOp for sessions idle for a long time: idle app servers holding pools open, forgotten mongosh sessions, or tools left connected.

3. Correlate with deploys: a deploy that started creating a client per request shows up as a step change.

4. Leak: share one client per process; close sessions and cursors explicitly.

5. Idle buildup: lower `maxIdleTimeMS` so idle connections recycle.

6. Genuine demand: raise `maxPoolSize` deliberately or scale the tier.

## When to use this

- You are seeing this exact error message; match the block above, not just part of it.
- The failing call matches the scenario in the title: Atlas.
- You want the fastest verified fix before digging through logs.

## When not to use this

- Your error text differs from the block above; close cousins often have different causes.
- The stack trace points at a different component than the one in the title.
- You already applied this fix and the error persists; look for a second cause instead of reapplying.

## Compatibility

- Not pinned to a specific version; follows current Atlas behavior.