Docker-in-Docker on Jenkins: Why Postgres Tests Can't Reach localhost (And How to Fix It)

Wed, 20 May 2026 00:00:00 +0000

Docker-in-Docker on Jenkins: Postgres Tests Can’t Reach localhost#

A Jenkins job runs docker run -d -p 5432:5432 postgres:17-alpine and gets back a container ID. The next step is psql -h localhost -p 5432 -U postgres and it returns Connection refused. The retry loop tries 30 times and gives up. The test job fails with “could not connect to server”.

If you’ve added longer waits, switched to --network host, or rewritten the test script to launch its own postgres container, none of that will help. The problem is the network model: Jenkins running in a Kubernetes pod uses the host’s docker socket to launch SIBLING containers. Those siblings live on the host’s docker bridge network, not in Jenkins’s pod network namespace. localhost from inside Jenkins is the pod’s loopback; the published port is on the host’s interface.

Jenkins Multibranch Silent Skip After Branch Recreate: Rename to Recover

Wed, 20 May 2026 00:00:00 +0000

Jenkins Multibranch Silent Skip After Branch Recreate#

Push a branch named fix/foo. Trigger a multibranch scan. The scan log shows Checking branch fix/foo and immediately moves to the next branch with no verdict line. No job appears under the multibranch. No build fires. Other branches scan and build normally.

This is Jenkins’s branch source plugin silently skipping a branch because its internal cache treats the name as a duplicate of a previously-deleted entry. The cache survives plugin restarts, multibranch rescans, and kubectl rollout restart jenkins. The reliable recovery is to push the same commits under a different branch name — the cache has no entry for the new name and processes it cleanly.

Jenkins-Debugging on Agent Zone

Docker-in-Docker on Jenkins: Why Postgres Tests Can't Reach localhost (And How to Fix It)

Docker-in-Docker on Jenkins: Postgres Tests Can’t Reach localhost#

Jenkins Multibranch Silent Skip After Branch Recreate: Rename to Recover

Jenkins Multibranch Silent Skip After Branch Recreate#