docker-py running container blocks access to "docker stats"

I am using docker-py to run a short-running (1m-2h) container in the background and I’d like to monitor that container’s stats to record and characterize its I/O, CPU, and memory usage every second or two. But it appears that while containers are running under docker-py I can’t get stats, either from my code through docker-py (c.stats()) or the command line docker stats. Streaming or no streaming, both seem to just hang until they timeout, or the container just happens to finish and unblock docker.

I should note that I can call other functions on the docker-py Client, such as containers(). Just that the stats() call with no streaming or attempting to iterate over the generator with streaming just hangs until the container exits. Similar story with the command line. docker ps works, docker stats hangs.

I’m using Ubuntu 14.04, docker-py version 1.9.0, and docker version 1.12.1, plain vanilla from the repos, connecting over a local domain socket as configured by default (/var/run/docker.sock).

[TomasTomecek]

So this is actually fixed in upstream: https://github.com/docker/docker/pull/25905

The problem is that container has disabled networking (SandboxID is set to "") and stat collector fails to pick networking stats (obviously) and won’t publish any stats to channel, meaning server will never respond with any stats.

To workaround this issue: enable networking. To fix this issue: wait for upstream to release a new version of docker (> 1.12.1).

[bartgrantham]

Wait! {'network_disabled' : False} did fix my problem! But it was masked by another important problem that might be related the source of the bug. In my code I iterate until the container disappears from the list of running containers:

while container['Id'] in [i['Id'] for i in c.containers()]:
        print c.stats(container['Id'], stream=False)
        time.sleep(2)

With {'network_disabled' : False} that loops correctly until the container is no longer running. Then, and I suspect there’s a race condition here, what should be the final call to stats() hangs. My solution is to set the client timeout to something smaller and less annoying like 15 seconds and do this:

    while container['Id'] in [i['Id'] for i in c.containers()]:
        try:
            stats = c.stats(container['Id'], stream=False)
        except:
            break
        print stats
        time.sleep(2)