Attribute "ports" on Container Does Not Include Ports

[ClaytonNorthey92]

I am running a (postgres) container using the Docker Python SDK.

I am trying to bind a random host port to port 5432 in the container. According to the documentation:

None, to assign a random host port. For example, {'2222/tcp': None}.

This is my setup:

import docker


if __name__ == '__main__':
    client = docker.from_env()
    container = client.containers.run('postgres:9.6', None,
        detach=True,
        ports= {
            '5432/tcp': None # bind to a random port
        },
        network_mode='bridge',
        environment={
            'POSTGRES_PASSWORD': 'password'
        },
    )

    print(container.attrs['NetworkSettings'])
    print(container.ports)

The output from the print statements:

{'Bridge': '', 'SandboxID': '', 'HairpinMode': False, 'LinkLocalIPv6Address': '', 'LinkLocalIPv6PrefixLen': 0, 'Ports': {}, 'SandboxKey': '', 'SecondaryIPAddresses': None, 'SecondaryIPv6Addresses': None, 'EndpointID': '', 'Gateway': '', 'GlobalIPv6Address': '', 'GlobalIPv6PrefixLen': 0, 'IPAddress': '', 'IPPrefixLen': 0, 'IPv6Gateway': '', 'MacAddress': '', 'Networks': {'bridge': {'IPAMConfig': None, 'Links': None, 'Aliases': None, 'NetworkID': '', 'EndpointID': '', 'Gateway': '', 'IPAddress': '', 'IPPrefixLen': 0, 'IPv6Gateway': '', 'GlobalIPv6Address': '', 'GlobalIPv6PrefixLen': 0, 'MacAddress': '', 'DriverOpts': None}}}
{}

According to this pull request the .ports property should have the mapped port.

Python version:

Python 3.7.9

Docker SDK version:

Name: docker
Version: 4.3.1

And I can verify that the container indeed does have a bound port:

$ docker ps
CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS              PORTS                     NAMES
e97a2bb377fb        postgres:9.6        "docker-entrypoint.s…"   3 seconds ago       Up 3 seconds        0.0.0.0:32780->5432/tcp   stupefied_hellman

[steffenhk]

I had the same problem. Adding a container.reload() after calling run() seems to refresh the ports dict.

[ClaytonNorthey92]

I think the issue I was seeing has to do with the container's state after you create the container via the docker API.

I used @steffenhk 's advice and used container.reload() like so:

print(container.attrs['State'])
container.reload()
print(container.attrs['State'])

and got the output...

{'Status': 'created', 'Running': False, 'Paused': False, 'Restarting': False, 'OOMKilled': False, 'Dead': False, 'Pid': 0, 'ExitCode': 0, 'Error': '', 'StartedAt': '0001-01-01T00:00:00Z', 'FinishedAt': '0001-01-01T00:00:00Z'}

{'Status': 'running', 'Running': True, 'Paused': False, 'Restarting': False, 'OOMKilled': False, 'Dead': False, 'Pid': 14020, 'ExitCode': 0, 'Error': '', 'StartedAt': '2020-12-14T21:27:13.0983733Z', 'FinishedAt': '0001-01-01T00:00:00Z', 'Health': {'Status': 'starting', 'FailingStreak': 0, 'Log': []}}

you can see on the first output, the container is not yet started (and thus wouldn't have a mapped port). but after the reload it is started, which would make sense that the ports are now mapped

One option would be to add a healthcheck, but even then you would have to poll the health status like this function does

tldr; this isn't an issue with the docker-py code, this is me not handling starting the postgres container correctly. I would need a separate way to determine the container was up and running (such as a healthcheck), then reload() and check the port number