The Fix
pip install urllib3==1.25.9
Based on closed urllib3/urllib3 issue #1758 · PR/commit linked
Production note: Most teams hit this during upgrades or environment changes. Roll out with a canary and smoke critical endpoints (health, OpenAPI/docs) before 100%.
@@ -698,9 +698,11 @@ def urlopen(
clean_exit = True
- except queue.Empty:
- # Timed out by queue.
- raise EmptyPoolError(self, "No pool connections are available.")
Option A — Upgrade to fixed release\npip install urllib3==1.25.9\nWhen NOT to use: Do not apply this fix if the pool behavior is expected to handle None values.\n\n
Why This Fix Works in Production
- Trigger: When pool is in blocking mode, there is no connections in pool, and getting connection from pool is timed out.
- Mechanism: The connection pool incorrectly inserts 'None' when no connections are available, leading to timeouts
- Why the fix works: Prevents inserting 'None' into the connection pool when it is empty, addressing the issue of established connections being replaced by None values. (first fixed release: 1.25.9).
- If left unfixed, the same config can fail only in production (env differences), causing startup failures or partial feature outages.
Why This Breaks in Prod
- The connection pool incorrectly inserts 'None' when no connections are available, leading to timeouts
- Production symptom (often without a traceback): When pool is in blocking mode, there is no connections in pool, and getting connection from pool is timed out.
Proof / Evidence
- GitHub issue: #1758
- Fix PR: https://github.com/urllib3/urllib3/pull/1866
- First fixed release: 1.25.9
- Reproduced locally: No (not executed)
- Last verified: 2026-02-09
- Confidence: 0.85
- Did this fix it?: Yes (upstream fix exists)
- Own content ratio: 0.81
Discussion
High-signal excerpts from the issue thread (symptoms, repros, edge-cases).
“Hello! When pool is in blocking mode, there is no connections in pool, and getting connection from pool is timed out. https://github.com/urllib3/urllib3/pull/1759”
Failure Signature (Search String)
- When pool is in blocking mode, there is no connections in pool, and getting connection from pool is timed out.
Copy-friendly signature
Failure Signature
-----------------
When pool is in blocking mode, there is no connections in pool, and getting connection from pool is timed out.
Error Message
Signature-only (no traceback captured)
Error Message
-------------
When pool is in blocking mode, there is no connections in pool, and getting connection from pool is timed out.
What Broke
Connections are replaced by None, causing timeouts when attempting to retrieve connections from the pool.
Why It Broke
The connection pool incorrectly inserts 'None' when no connections are available, leading to timeouts
Fix Options (Details)
Option A — Upgrade to fixed release Safe default (recommended)
pip install urllib3==1.25.9
Use when you can deploy the upstream fix. It is usually lower-risk than long-lived workarounds.
Fix reference: https://github.com/urllib3/urllib3/pull/1866
First fixed release: 1.25.9
Last verified: 2026-02-09. Validate in your environment.
When NOT to Use This Fix
- Do not apply this fix if the pool behavior is expected to handle None values.
Did This Fix Work in Your Case?
Quick signal helps us prioritize which fixes to verify and improve.
Prevention
- Add a CI check that diffs key outputs after upgrades (OpenAPI schema snapshots, JSON payload shapes, CLI output).
- Upgrade behind a canary and run integration tests against the canary before 100% rollout.
- Add a stress test that runs high-concurrency workloads and fails on thread dumps / blocked locks.
- Enable watchdog dumps in prod (faulthandler, thread dump endpoint) to capture deadlocks quickly.
Version Compatibility Table
| Version | Status |
|---|---|
| 1.25.9 | Fixed |
Related Issues
No related fixes found.
Sources
We don’t republish the full GitHub discussion text. Use the links above for context.