Context :

• Slaves are provisioned by a docker swarm
• /var/run/docker.sock mounted in slaves containers
• Slaves base image contains a readable docker.json with auth correctly configured

A shell step with docker push <registry>:<image> fails with permission denied.

This is due to the DOCKER_HOST variable that is set during exec, the docker engine doesn't use the local docker.sock & local docker.json config.

Removing this variable with unset DOCKER_HOST before the docker push solves the issue.

I don't know if some people might need that variable but the behavior must be configurable somehow.