How to get logs for docker maintenance tasks in preparation

Question

Now I am playing with docker 1.12, created a service and noticed that there is a "preparing" step when I launched "docker service tasks xxx" .

I can only guess that at this stage the images are stretched or updated.

My question is: how can I see the magazines for this stage? Or more generally: how can I see the logs for docker service tasks?

Answer 1

I use a docker machine to emulate different "hosts" in my development environment.

This is what I did to find out what is going on at this stage of the “Preparation” for my services:

docker service ps <serviceName>

You should see the nodes (machines) where your service was supposed to start. Here you will see the message "Preparation".

Use the ssh dock machine to connect to a specific machine:

 docker-machine ssh <nameOfNode/Machine> 

Your invitation will change. You are now inside another machine. Inside this other machine, do the following:

tail -f /var/log/docker.log

You will see a demon log for this machine. There you will see if this particular daemon does "pull" or what it does in preparation for the service. In my case, I found something like this:

time="2016-09-05T19:04:07.881790998Z" level=debug msg="pull progress map[progress:[===========================================> ] 112.4 MB/130.2 MB status:Downloading

Which made me realize that it was just downloading some images from my docker account.

Answer 2

Your assumption (about stretching during preparation) is correct.

There is no log command for tasks yet, but you can probably connect to this daemon and make docker logs usual way.