How to Resolve Code Server Startup Failures Due to Pex Version Issues

Last updated: October 16, 2025

If you encounter deployment failures with the error Exception: Code server failed to start up or connection pool is full, this may be due to compatibility issues with Pex version 2.60.0.

To resolve this issue:

  1. Check your base image and CI/CD configuration

  2. Pin your Pex version to a version prior to 2.60.0

  3. If using dagster-cloud[serverless], update to version 1.11.15 or later which automatically handles Pex version constraints

This issue typically occurs after updating base images or dependencies that might pull in Pex 2.60.0. Even if deployments initially succeed after an update, issues may surface in subsequent deployments.

For more information about this issue, you can refer to the related Pex issue tracker: PEX Issue #2942