ddebug (docker debug)

ddebug is a super simple script that helps debugging containers that are running, but either have a read-only rootfs or missing tools required to debug.

It creates a new container that shares a network, pid and ipc namespace with the target container, and will additionally mount the target containers root filesystem into the debug container, and /containerfs.

By default, it will create an alpine based container. You can change this by specifying an alternate image as a second positional parameter.

Usage

First, login to the host that is running your target container, or configure your local docker client to talk to the remote machines daemon.

You'll then want to get the ID or name of the container you intend to debug:

$ docker ps
CONTAINER ID        IMAGE                                   COMMAND                  CREATED             STATUS              PORTS                    NAMES
a55225460627        gcr.io/cloudsql-docker/gce-proxy:1.10   "/cloud_sql_proxy ..."   2 days ago          Up 2 days           0.0.0.0:3306->3306/tcp   epic_kepler

Now run ddebug using the containers ID (here a55225460627), or name (epic_kepler):

$ ddebug.sh epic_kepler

You can optionally override the debug image used like so:

$ ddebug.sh epic_kepler debian:jessie

Running ddebug in Docker

If you want to make it easy to run ddebug without having to upload a script to your hosts, or if you want to execute ddebug without having to SSH/configure your docker daemon (i.e. via Kubernetes), a Docker image for ddebug has been made available on Dockerhub. You can try this out with:

$ docker run --rm -it \
	-v $(which docker):/usr/bin/docker \
	-v /var/run/docker.sock:/var/run/docker.sock \
	munnerz/ddebug epic_kepler

This should immediately drop you into a debugging shell.

NOTE: if using OSX under Docker for Mac, you must replace $(which docker) with the absolute path to the docker binary within the Moby VM, something like:

$ docker run --rm -it \
	-v /usr/bin/docker:/usr/bin/docker \
	-v /var/run/docker.sock:/var/run/docker.sock \
	munnerz/ddebug epic_kepler