urllib3 Ubuntu 20.04 (OpenSSL 1.1.1) 2.7

The Fix

pip install urllib3==2.0.0a4

Based on closed urllib3/urllib3 issue #2975 · 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%.

Jump to Verify Open PR/Commit

@@ -98,7 +98,12 @@ jobs:
           cache: "pip"
 
-      - name: "Install dependencies"
+      - if: matrix.python-version == '2.7'
+        name: "Install dependencies"

repro.py

nox > Running session unsupported_setup_py-2.7
nox > Creating virtual environment (virtualenv) using python2.7 in .nox/unsupported_setup_py-2-7
nox > Command /opt/hostedtoolcache/Python/3.11.3/x64/bin/python -m virtualenv /home/runner/work/urllib3/urllib3/.nox/unsupported_setup_py-2-7 -p python2.7 failed with exit code 1:
RuntimeError: failed to find interpreter for Builtin discover of python_spec='python2.7'
nox > Session unsupported_setup_py-2.7 failed.

verify

Re-run the minimal reproduction on your broken version, then apply the fix and re-run.

fix.md

Option A — Upgrade to fixed release\npip install urllib3==2.0.0a4\nWhen NOT to use: Do not use if it changes public behavior or if the failure cannot be reproduced.\n\n

Why This Fix Works in Production

Trigger: nox > Running session unsupported_setup_py-2.7
Mechanism: Pins the virtualenv version to fix the Python 2.7 CI job failure.
Why the fix works: Pins the virtualenv version to fix the Python 2.7 CI job failure. (first fixed release: 2.0.0a4).

Production impact:

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

Shows up under Python 2.7 in real deployments (not just unit tests).
Surfaces as: nox > Running session unsupported_setup_py-2.7

Proof / Evidence

GitHub issue: #2975
Fix PR: https://github.com/urllib3/urllib3/pull/2977
First fixed release: 2.0.0a4
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.85
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.48

Discussion

High-signal excerpts from the issue thread (symptoms, repros, edge-cases).

Jump to Sources Open on GitHub

“the cause is https://virtualenv.pypa.io/en/latest/changelog.html#features-20-22-0 https://github.com/pypa/virtualenv/pull/2548”

@graingert · 2023-04-20 · source

Failure Signature (Search String)

nox > Running session unsupported_setup_py-2.7

Error Message

Stack trace

error.txt

Error Message
-------------
nox > Running session unsupported_setup_py-2.7
nox > Creating virtual environment (virtualenv) using python2.7 in .nox/unsupported_setup_py-2-7
nox > Command /opt/hostedtoolcache/Python/3.11.3/x64/bin/python -m virtualenv /home/runner/work/urllib3/urllib3/.nox/unsupported_setup_py-2-7 -p python2.7 failed with exit code 1:
RuntimeError: failed to find interpreter for Builtin discover of python_spec='python2.7'
nox > Session unsupported_setup_py-2.7 failed.

Minimal Reproduction

repro.py

nox > Running session unsupported_setup_py-2.7
nox > Creating virtual environment (virtualenv) using python2.7 in .nox/unsupported_setup_py-2-7
nox > Command /opt/hostedtoolcache/Python/3.11.3/x64/bin/python -m virtualenv /home/runner/work/urllib3/urllib3/.nox/unsupported_setup_py-2-7 -p python2.7 failed with exit code 1:
RuntimeError: failed to find interpreter for Builtin discover of python_spec='python2.7'
nox > Session unsupported_setup_py-2.7 failed.

Environment

Python: 2.7

What Broke

CI jobs fail to run, causing delays in testing and deployment.

Fix Options (Details)

Option A — Upgrade to fixed release Safe default (recommended)

pip install urllib3==2.0.0a4

When NOT to use: Do not use if it changes public behavior or if the failure cannot be reproduced.

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/2977

First fixed release: 2.0.0a4

Last verified: 2026-02-09. Validate in your environment.

When NOT to Use This Fix

Do not use if it changes public behavior or if the failure cannot be reproduced.

Verify Fix

verify

Re-run the minimal reproduction on your broken version, then apply the fix and re-run.

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 TLS smoke test that performs a real handshake in CI (include CA bundle validation and hostname checks).
Alert on handshake failures by error string and endpoint to catch cert/CA changes quickly.

Version Compatibility Table

Version	Status
2.0.0a4	Fixed

Related Issues

No related fixes found.

Cluster: urllib3:configuration-error urllib3 hub urllib3 best practices All hubs All clusters

Related clusters: Data consistency SSL handshake Other

Sources

We don’t republish the full GitHub discussion text. Use the links above for context.

urllib3 Ubuntu 20.04 (OpenSSL 1.1.1) 2.7 unsupported_setup_py CI job fails (Fix)