[openstack-dev] [kolla] Diagnosing problems with containers

2014-09-26 Thread Lars Kellogg-Stedman
As people are starting to look at Kubernetes and Docker, there have
been a number of questions regarding how to diagnose problems with
containers.  Here are a few useful hints:

## Docker logs

Docker captures stdout/stderr from the main process and makes this
available via the `docker log` command.  That is, if your Dockerfile
looks like this:

FROM fedora
RUN yum -y install mariadb; yum clean all
CMD mysql --this-is-a-terrible-idea

And you were to have Kubernetes launch an image built from that file
and wanted to diagnose why it wasn't working, you could run `docker
logs container_name_or_id` and see:

mysql: unknown option '--this-is-a-terrible-idea'

## Using 'nsenter'

The `nsenter` command is available in recent coreutils packages.  It
allows you to run commands inside existing namespaces.  

A useful shortcut is to place the following inside a script and call
it docker-enter:

#!/bin/sh
nsenter -t $(docker inspect \
  --format '{{ .State.Pid }}' $CONTAINER) \
  -m -u -i -n -p -w $@

Now you can run `docker-enter container_name_or_id` to start a shell
inside the specified container.

Once inside the container, you may want to see the environment
variables passed to PID 1 to ensure that service discovery is
operating correctly.  You can do that via:

tr '\000' '\012'  /proc/1/environ

You can of course inspect anything on the filesystem, although ideally
your application is logging to stdout/stderr and not to local files.
If you know your container's ENTRYPOINT and CMD entries, you can run
those by hand to see exactly what is happening.

-- 
Lars Kellogg-Stedman l...@redhat.com | larsks @ {freenode,twitter,github}
Cloud Engineering / OpenStack  | http://blog.oddbit.com/



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Re: [openstack-dev] [kolla] Diagnosing problems with containers

2014-09-26 Thread Chmouel Boudjnah
On Fri, Sep 26, 2014 at 4:29 PM, Lars Kellogg-Stedman l...@redhat.com
wrote:

 As people are starting to look at Kubernetes and Docker, there have



Nice, thanks for sharing! I think that may be nice to have this in a blog
article (if it wasn't done already)

Chmouel
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