is it possible to start the container in detached mode and attach to print the output in a loop?

[dberardo-com]

i mean somethings like this:

await container.start(detach=True)  # this line should return immediately
async for chunk in container.log(stdout=True, stderr=os.environ.get("PRINT_WARNINGS",0), follow=True):
    print(chunk, end='')
error_log=[]

container cmd is "sleep 1 && echo 1 && sleep 20 && echo 20"

this means that the async loop will output 2 echo messages, one after 1 second and one after 20 seconds.

[dberardo-com]

the problem is that running with detached lead to this error: https://stackoverflow.com/questions/44515097/starting-container-using-docker-api

[Naufal Afif]

hi @dberardo-com

in docker-sdk / library, container is running in detached mode by default. so you dont have to specify it.

the problem is that running with detached lead to this error: https://stackoverflow.com/questions/44515097/starting-container-using-docker-api

this issue is happened because container.start is to start created container & doesn't accept any argument, the config should be provided in container.create. you can refer it to API doc https://docs.docker.com/engine/api/v1.42/#tag/Container/operation/ContainerStart

[Naufal Afif]

if you want to print the output in a loop, you can use container.attach or container.websocket

[Naufal Afif]

you can also do it using container exec

[dberardo-com]

thanks for the reply, i had already tried adding these params to the config object i pass to the create method, here:

await docker.containers.create(
          config={
              "Detach": True,
          },
      )

but then when i call the .start method, the python script awaits till the whole execution of the start command is finished, before proceeding ... which is exactly what i want to avoid.

any guess?

---

INFO: i was looking here and could not find any option to set the detached flag while creating the container: https://aiodocker.readthedocs.io/en/latest/_modules/aiodocker/containers.html#DockerContainers.create

btw the reason why i need to do this, is that i have to use the "docker copy" command equivalent before starting the container to copy files inside it upfront. if there is a way to do this all in one command, that would be welcome, otherwise my current approach was:

• create()
• put_archive()
• start(detached=True) --> error

[Naufal Afif]

Hi @dberardo-com

there's no need to put detached when creating container, it is running detached by default.

here's some example code that print the logs in a loop

import aiodocker

docker = aiodocker.Docker()
print('== Running a hello-world container ==')
container = await docker.containers.create_or_replace(
    config={
        'Cmd': ['/bin/bash', '-c', 'sleep 3600'],
        'Image': 'ubuntu:latest',
    },
    name='testing',
)
await container.start()

try:
    # code here
    socket = await container.exec(
        stdout=True,
        stderr=True,
        tty=True,
        cmd=["/bin/echo", '"hello world"'],
    )
    socket_stream = socket.start(detach=False)
    await socket_stream._init()

    while True:
        output = await socket_stream.read_out()
        if output:
            print(output)
        else:
            break
except Exception as e:
    print(e)


await container.delete(force=True)
await docker.close()

[dberardo-com]

i am totally sorry ... i have just realised that both your solution and mine from above were working .. but that i was not seeing any output because of this env variable not being set:

PYTHONUNBUFFERED=1

so the issue was related to the buffered output ...

thanks again for your support

[Naufal Afif]

Hi @dberardo-com , glad to hear that. i think you can close this issue