Bug: `K3SContainer` does not support other connection modes (in `get_container_host_ip`)

[ndellosa95]

Describe the bug

K3SContainer calls get_container_host_ip in its __init__ method here and here before the container is started, causing it to fail with an AssertionError here.

To Reproduce

from testcontainers.k3s import K3SContainer

with K3SContainer() as k3s:
     print("gonna throw an error before I even get here :(")

Runtime environment

I'm on an ARM Mac and this is in Python 3.12, but that shouldn't make a difference.

[alexanderankin]

If there is a bug, it was probably introduced with the new waiting strategies, thanks for reporting, I'll take a look

…

On Wed, Aug 13, 2025, 5:19 PM ndellosa95 ***@***.***> wrote: *ndellosa95* created an issue (testcontainers/testcontainers-python#861) <#861> *Describe the bug* K3SContainer calls get_container_host_ip in its __init__ method here and here <https://github.com/testcontainers/testcontainers-python/blob/main/modules/k3s/testcontainers/k3s/__init__.py#L45-L46> before the container is started, causing it to fail with an AssertionError here <https://github.com/testcontainers/testcontainers-python/blame/main/core/testcontainers/core/container.py#L229-L231> . *To Reproduce* from testcontainers.k3s import K3SContainer with K3SContainer() as k3s: print("gonna throw an error before I even get here :(") *Runtime environment* I'm on an ARM Mac and this is in Python 3.12, but that shouldn't make a difference. — Reply to this email directly, view it on GitHub <#861>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/ACECGJGKK2FYZLF55ITU6ML3NOTVJAVCNFSM6AAAAACD23I4WKVHI2DSMVQWIX3LMV43ASLTON2WKOZTGMYTSOJTGA3TQNY> . You are receiving this because you are subscribed to this thread.Message ID: ***@***.***>

[alexanderankin]

oh, seems like we have to re-think container modes - or k3s - the new container modes that try to help address dind/dood are not compatible with the k3s container. ill move the assert inside the if branches that need it, and then it will work by default (not dind or dood or whatever0

…

On Wed, Aug 13, 2025 at 6:07 PM David Ankin ***@***.***> wrote: If there is a bug, it was probably introduced with the new waiting strategies, thanks for reporting, I'll take a look On Wed, Aug 13, 2025, 5:19 PM ndellosa95 ***@***.***> wrote: > *ndellosa95* created an issue (testcontainers/testcontainers-python#861) > <#861> > > *Describe the bug* > > K3SContainer calls get_container_host_ip in its __init__ method here and > here > <https://github.com/testcontainers/testcontainers-python/blob/main/modules/k3s/testcontainers/k3s/__init__.py#L45-L46> > before the container is started, causing it to fail with an > AssertionError here > <https://github.com/testcontainers/testcontainers-python/blame/main/core/testcontainers/core/container.py#L229-L231> > . > > *To Reproduce* > > from testcontainers.k3s import K3SContainer > with K3SContainer() as k3s: > print("gonna throw an error before I even get here :(") > > *Runtime environment* > > I'm on an ARM Mac and this is in Python 3.12, but that shouldn't make a > difference. > > — > Reply to this email directly, view it on GitHub > <#861>, or > unsubscribe > <https://github.com/notifications/unsubscribe-auth/ACECGJGKK2FYZLF55ITU6ML3NOTVJAVCNFSM6AAAAACD23I4WKVHI2DSMVQWIX3LMV43ASLTON2WKOZTGMYTSOJTGA3TQNY> > . > You are receiving this because you are subscribed to this thread.Message > ID: ***@***.***> >

[alexanderankin]

#862

[marbon87]

Still having the same error with 4.13.0:

_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
.venv/lib/python3.12/site-packages/testcontainers/k3s/__init__.py:45: in __init__
    self.with_env("K3S_URL", f"https://{self.get_container_host_ip()}:{self.KUBE_SECURE_PORT}")
                                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

self = <testcontainers.k3s.K3SContainer object at 0x7f087cac1250>

    def get_container_host_ip(self) -> str:
        connection_mode: ConnectionMode
        connection_mode = self.get_docker_client().get_connection_mode()
    
        if connection_mode == ConnectionMode.docker_host:
            return self.get_docker_client().host()
        elif connection_mode == ConnectionMode.gateway_ip:
            # mypy:
            container = self._container
>           assert container is not None
                   ^^^^^^^^^^^^^^^^^^^^^
E           AssertionError

[alexanderankin]

the fact that k3scontainer does not support other connection modes is not an issue with the core library, thats an issue with the community module. PR's welcome. before we introduced this change, this should have never worked with dind in the first place - connection modes allow for use of gateway_ip specifically. so in this case you can set the connection mode to docker_host and see if that works, otherwise we have to think together about how to solve this - getting the container's private ip before it exists - dont think this is possible. I believe the earlier behavior was just using connection mode = docker host

[marbon87]

Hi @alexanderankin ,

setting the conncetion-mode to docker_host with

os.environ["TESTCONTAINERS_CONNECTION_MODE"] = "docker_host"
from testcontainers.k3s import K3SContainer

does solve the problem.