2a2f10f2e9
DockerBuildRunner appended TESTCONTAINERS_HOST_OVERRIDE=localhost after the docker.env entries, so a host could not name another address. A rootless daemon with the slirp4netns port driver publishes ports on 10.0.2.100; vm4006 needs exactly that since its daemon switched. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Co-authored-by: mhoennig <michael@hoennig.de> Reviewed-on: #85
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WARNING: This document describes only the change applied in this PR. It may already be outdated once the next PR is merged. Historic PR-documentation is not maintained along with new PRs — treat it as a snapshot, not as current documentation.
The Problem
Since 2026-10-01 every Testcontainers test of hs.hsadmin.ng fails on vm4006 with "Connection to localhost: refused".
The rootless Docker daemon there runs with the slirp4netns port driver now: its unit was rewritten on 2026-09-23 and took effect at a reboot.
With this driver, docker-proxy listens on the child address 10.0.2.100 inside the daemon's network namespace, not on localhost.
A build container with network: host lives in that namespace, so Testcontainers must connect to 10.0.2.100.
The host set TESTCONTAINERS_HOST_OVERRIDE: "10.0.2.100" in docker.env, but DockerBuildRunner appended its own TESTCONTAINERS_HOST_OVERRIDE=localhost after it, and the last --env wins.
Non-Goals
- No detection of the port driver; the host knows its daemon, and one line in the machine config says so.
- No change to the default for hosts that set nothing.
The Scenarios
Feature: the host decides where Testcontainers reaches its ports
Scenario#85.01: A host override in docker.env wins
So that a host whose daemon publishes ports elsewhere can say so, and undo it by deleting the line.
- Given a build with
TESTCONTAINERS_HOST_OVERRIDEindocker.env - When Werkator starts its container
- Then the container gets that value, once
- Given no such entry, then the default stays:
localhostwithnetwork: host,host.docker.internalotherwise
Verified by
- DockerBuildRunnerTest — the override from
docker.envpassed once; the existing default tests for host and bridge networks
The Solution
DockerBuildRunner.runArgs appends its default TESTCONTAINERS_HOST_OVERRIDE only when docker.env has none.
Switching back is a configuration change, not a Werkator update: should the daemon go back to the builtin port driver, the host deletes its entry and the default applies again.
Additional Changes
docs/configuration.mdand the architecture skill describe the default and the override.- Version 1.24.1 with its release note.