testcontainers / testcontainers/testcontainers-python

Bug: `docker.errors.DockerException: Error while fetching server API version: maximum recursion depth exceeded` since upgrade of 4.15

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Description

Describe the bug

It seems there is a regression after upgrading from 4.14.2 to 4.15

I was able to reproduce locally (podman) and on Kubernetes (via kubedock) and DOCKER_HOST='tcp://localhost:2475'

To Reproduce

def test_containers():
    with PostgresContainer(
        "<custom_domain>/postgres:16.4"
    ) as postgres:
        engine = sqlalchemy.create_engine(postgres.get_connection_url())
        with engine.begin() as connection:
            result = connection.execute(sqlalchemy.text("select version()"))
            (version,) = result.fetchone()
            client = TestClient(app)
            response = client.get("/api/todos/1")
            assert response.status_code == 200
            assert response.json() == {"completed": False, "id": 1, "title": "Todo 1"}
            response = client.get("/api/todos")
            assert response.status_code == 200

FAILED app/test_main.py::test_containers - docker.errors.DockerException: Error while fetching server API version: maximum recursion depth exceeded

Runtime environment

WSL podman but same behavior on kubedock (Docker API for K8S)

# Get the operating system information (on a unix os).
$ uname -a
 6.18.33.2-microsoft-standard-WSL2 #1
# Get the python version.
$ python --version
Python 3.14.5
# Get the docker version and other docker information.
$ docker info
version:
  APIVersion: 4.9.3
  Built: 0
  BuiltTime: Thu Jan  1 01:00:00 1970
  GitCommit: ""
  GoVersion: go1.22.2
  Os: linux
  OsArch: linux/amd64
  Version: 4.9.3
# Get all python packages.
$ pip freeze
annotated-doc==0.0.4
annotated-types==0.7.0
anyio==4.14.1
babel==2.18.0
backrefs==7.0
beautifulsoup4==4.12.3
certifi==2026.6.17
cfgv==3.5.0
charset-normalizer==3.4.9
click==8.4.1
colorama==0.4.6
coverage==7.15.0
dacite==1.9.2
defusedxml==0.7.1
distlib==0.4.3
docker==7.1.0
fastapi==0.139.2
filelock==3.29.7
ghp-import==2.1.0
gitdb==4.0.12
GitPython==3.1.50
greenlet==3.5.3
h11==0.16.0
httpcore==1.0.9
httpie==3.2.4
httpx==0.28.1
identify==2.6.19
idna==3.18
iniconfig==2.3.0
Jinja2==3.1.6
Markdown==3.10.2
markdown-it-py==4.2.0
markdown_graphviz_inline==1.1.3
MarkupSafe==3.0.3
mdurl==0.1.2
mdx-truly-sane-lists==1.3
mergedeep==1.3.4
mkdocs==1.6.1
mkdocs-autorefs==1.4.4
mkdocs-get-deps==0.2.2
mkdocs-git-latest-changes-plugin==0.0.23
mkdocs-github-admonitions-plugin==0.1.1
mkdocs-include-dir-to-nav==1.2.0
mkdocs-inline-svg-plugin==0.1.5
mkdocs-kroki-plugin==1.6.0
mkdocs-material==9.7.6
mkdocs-material-extensions==1.3.1
mkdocs-monorepo-plugin==1.1.2
mkdocs-multirepo-plugin==0.8.3
mkdocs-nav-weight==0.3.0
mkdocs-redirects==1.2.3
mkdocs-same-dir==0.1.5
mkdocs-techdocs-core==1.7.0
mkdocstrings==1.0.4
multidict==6.7.1
mypy_extensions==1.1.0
nodeenv==1.10.0
packaging==26.2
paginate==0.5.7
pathspec==1.1.1
plantuml-markdown==3.11.2
platformdirs==4.10.0
pluggy==1.6.0
pre_commit==4.6.1
properdocs==1.6.7
psycopg2-binary==2.9.12
pydantic==2.13.4
pydantic_core==2.46.4
Pygments==2.20.0
pymdown-extensions==10.21.3
PySocks==1.7.1
pytest==9.1.1
pytest-cov==7.1.0
python-dateutil==2.9.0.post0
python-discovery==1.4.3
python-dotenv==1.2.2
python-slugify==8.0.4
PyYAML==6.0.3
pyyaml_env_tag==1.1
requests==2.31.0
requests-toolbelt==1.0.0
result==0.17.0
rich==15.0.0
setuptools==83.0.0
six==1.17.0
smmap==5.0.3
soupsieve==2.8.4
SQLAlchemy==2.0.51
starlette==1.3.1
testcontainers==4.15.0
text-unidecode==1.3
typing-inspect==0.8.0
typing-inspection==0.4.2
typing_extensions==4.16.0
urllib3==2.7.0
uvicorn==0.51.0
virtualenv==21.6.0
watchdog==6.0.0
wrapt==2.2.2

On 4.14.2 no issue on both environment

On CI I was able to capture this stacktrace

[05:43:48.711+02:00] - ../../../.local/lib/python3.14/site-packages/testcontainers/core/container.py:501: in _create_instance
[05:43:48.711+02:00] -     .start()
[05:43:48.711+02:00] -      ^^^^^^^
[05:43:48.711+02:00] - ../../../.local/lib/python3.14/site-packages/testcontainers/core/container.py:247: in start
[05:43:48.711+02:00] -     Reaper.get_instance()
[05:43:48.711+02:00] - ../../../.local/lib/python3.14/site-packages/testcontainers/core/container.py:472: in get_instance
[05:43:48.711+02:00] -     Reaper._instance = Reaper._create_instance()
[05:43:48.711+02:00] -                        ^^^^^^^^^^^^^^^^^^^^^^^^^
[05:43:48.711+02:00] - ../../../.local/lib/python3.14/site-packages/testcontainers/core/container.py:501: in _create_instance
[05:43:48.711+02:00] -     .start()
[05:43:48.711+02:00] -      ^^^^^^^
[05:43:48.711+02:00] - ../../../.local/lib/python3.14/site-packages/testcontainers/core/container.py:247: in start
[05:43:48.711+02:00] -     Reaper.get_instance()
[05:43:48.711+02:00] - ../../../.local/lib/python3.14/site-packages/testcontainers/core/container.py:472: in get_instance
[05:43:48.711+02:00] -     Reaper._instance = Reaper._create_instance()
[05:43:48.711+02:00] -                        ^^^^^^^^^^^^^^^^^^^^^^^^^
[05:43:48.711+02:00] - ../../../.local/lib/python3.14/site-packages/testcontainers/core/container.py:501: in _create_instance
[05:43:48.711+02:00] -     .start()
[05:43:48.711+02:00] -      ^^^^^^^
[05:43:48.711+02:00] - ../../../.local/lib/python3.14/site-packages/testcontainers/core/container.py:247: in start
[05:43:48.711+02:00] -     Reaper.get_instance()
[05:43:48.711+02:00] - ../../../.local/lib/python3.14/site-packages/testcontainers/core/container.py:472: in get_instance
[05:43:48.711+02:00] -     Reaper._instance = Reaper._create_instance()
[05:43:48.711+02:00] -                        ^^^^^^^^^^^^^^^^^^^^^^^^^
[05:43:48.711+02:00] - ../../../.local/lib/python3.14/site-packages/testcontainers/core/container.py:501: in _create_instance
[05:43:48.711+02:00] -     .start()
[05:43:48.711+02:00] -      ^^^^^^^
[05:43:48.711+02:00] - ../../../.local/lib/python3.14/site-packages/testcontainers/core/container.py:247: in start
[05:43:48.711+02:00] -     Reaper.get_instance()
[05:43:48.711+02:00] - ../../../.local/lib/python3.14/site-packages/testcontainers/core/container.py:472: in get_instance
[05:43:48.711+02:00] -     Reaper._instance = Reaper._create_instance()
[05:43:48.711+02:00] -                        ^^^^^^^^^^^^^^^^^^^^^^^^^
[05:43:48.711+02:00] - ../../../.local/lib/python3.14/site-packages/testcontainers/core/container.py:501: in _create_instance
[05:43:48.711+02:00] -     .start()
[05:43:48.711+02:00] -      ^^^^^^^
[05:43:48.711+02:00] - ../../../.local/lib/python3.14/site-packages/testcontainers/core/container.py:247: in start
[05:43:48.711+02:00] -     Reaper.get_instance()
[05:43:48.711+02:00] - ../../../.local/lib/python3.14/site-packages/testcontainers/core/container.py:472: in get_instance
[05:43:48.711+02:00] -     Reaper._instance = Reaper._create_instance()
[05:43:48.711+02:00] -                        ^^^^^^^^^^^^^^^^^^^^^^^^^
[05:43:48.711+02:00] - ../../../.local/lib/python3.14/site-packages/testcontainers/core/container.py:501: in _create_instance
[05:43:48.711+02:00] -     .start()
[05:43:48.711+02:00] -      ^^^^^^^
[05:43:48.711+02:00] - ../../../.local/lib/python3.14/site-packages/testcontainers/core/container.py:247: in start
[05:43:48.711+02:00] -     Reaper.get_instance()
[05:43:48.711+02:00] - ../../../.local/lib/python3.14/site-packages/testcontainers/core/container.py:472: in get_instance
[05:43:48.711+02:00] -     Reaper._instance = Reaper._create_instance()
[05:43:48.711+02:00] -                        ^^^^^^^^^^^^^^^^^^^^^^^^^
[05:43:48.711+02:00] - ../../../.local/lib/python3.14/site-packages/testcontainers/core/container.py:495: in _create_instance
[05:43:48.711+02:00] -     DockerContainer(c.ryuk_image)
[05:43:48.711+02:00] - ../../../.local/lib/python3.14/site-packages/testcontainers/core/container.py:129: in __init__
[05:43:48.711+02:00] -     self._docker = DockerClient(**(docker_client_kw or {}))
[05:43:48.711+02:00] -                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[05:43:48.711+02:00] - ../../../.local/lib/python3.14/site-packages/testcontainers/core/docker_client.py:194: in __init__
[05:43:48.712+02:00] -     self.client = docker.from_env(**kwargs)
[05:43:48.712+02:00] -                   ^^^^^^^^^^^^^^^^^^^^^^^^^
[05:43:48.712+02:00] - ../../../.local/lib/python3.14/site-packages/docker/client.py:110: in from_env
[05:43:48.712+02:00] -     return cls(
[05:43:48.712+02:00] - ../../../.local/lib/python3.14/site-packages/docker/client.py:48: in __init__
[05:43:48.712+02:00] -     self.api = APIClient(*args, **kwargs)
[05:43:48.712+02:00] -                ^^^^^^^^^^^^^^^^^^^^^^^^^^
[05:43:48.712+02:00] - ../../../.local/lib/python3.14/site-packages/docker/api/client.py:207: in __init__
[05:43:48.712+02:00] -     self._version = self._retrieve_server_version()
[05:43:48.712+02:00] -                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[05:43:48.712+02:00] - _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
[05:43:48.712+02:00] - 
[05:43:48.712+02:00] - self = <docker.api.client.APIClient object at 0x7f97b2161650>
[05:43:48.712+02:00] - 
[05:43:48.712+02:00] -     def _retrieve_server_version(self):
[05:43:48.712+02:00] -         try:
[05:43:48.712+02:00] -             return self.version(api_version=False)["ApiVersion"]
[05:43:48.712+02:00] -         except KeyError as ke:
[05:43:48.712+02:00] -             raise DockerException(
[05:43:48.712+02:00] -                 'Invalid response from docker daemon: key "ApiVersion"'
[05:43:48.712+02:00] -                 ' is missing.'
[05:43:48.712+02:00] -             ) from ke
[05:43:48.712+02:00] -         except Exception as e:
[05:43:48.712+02:00] - >           raise DockerException(
[05:43:48.712+02:00] -                 f'Error while fetching server API version: {e}'
[05:43:48.712+02:00] -             ) from e
[05:43:48.712+02:00] - E           docker.errors.DockerException: Error while fetching server API version: maximum recursion depth exceeded
[05:43:48.712+02:00] - 
[05:43:48.712+02:00] - ../../../.local/lib/python3.14/site-packages/docker/api/client.py:230: DockerException

Reaper._create_instance() seems to be called forever

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

First inspect testcontainers/core/container.py at Reaper.get_instance(), _create_instance(), and DockerContainer.init, then follow DockerClient construction into docker/api/client.py's _retrieve_server_version shown in the trace. Reproduce with the supplied test_containers example and DOCKER_HOST; done means the 4.15 path no longer recurses and the regression is covered.

Written by the indexing model from the issue text.

Assessment

Tech stack
docker, python
Domain
testing
Issue type
Bug
Difficulty
3/5
Estimated time
1-2 days
Activity status
Quiet
Clarity
Mostly clear
Newbie friendliness
58/100

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