Building docker image, inside an alpine linux container - docker

Question

We are using docker containers running alpine linux as build agents in bamboo. As part of the build plan a docker image needs to be created.
Our build agent has docker installed, however we are getting errors as the docker daemon isn't running. Starting the daemon with
/usr/local/bin/dockerd
gives the following:
INFO[0000] libcontainerd: new containerd process, pid: 640
ERRO[0001] 'overlay' is not supported over overlayfs
INFO[0001] Graph migration to content-addressability took 0.00 seconds
INFO[0001] Loading containers: start.
WARN[0001] Running modprobe bridge br_netfilter failed with message: modprobe: can't change directory to '/lib/modules': No such file or directory
, error: exit status 1
WARN[0001] Running modprobe nf_nat failed with message: `modprobe: can't change directory to '/lib/modules': No such file or directory`, error: exit status 1
WARN[0001] Running modprobe xt_conntrack failed with message: `modprobe: can't change directory to '/lib/modules': No such file or directory`, error: exit status 1
Error starting daemon: Error initializing network controller: error obtaining controller instance: failed to create NAT chain: Iptables not found
To try and get round this I've installed iptables. Now when I try to run the docker daemon I get:
INFO[0000] libcontainerd: new containerd process, pid: 705
ERRO[0001] 'overlay' is not supported over overlayfs
INFO[0001] Graph migration to content-addressability took 0.00 seconds
INFO[0001] Loading containers: start.
WARN[0001] Running modprobe bridge br_netfilter failed with message: modprobe: can't change directory to '/lib/modules': No such file or directory
, error: exit status 1
WARN[0001] Running modprobe nf_nat failed with message: `modprobe: can't change directory to '/lib/modules': No such file or directory`, error: exit status 1
WARN[0001] Running modprobe xt_conntrack failed with message: `modprobe: can't change directory to '/lib/modules': No such file or directory`, error: exit status 1
Error starting daemon: Error initializing network controller: error obtaining controller instance: failed to create NAT chain: iptables failed: iptables -t nat -N DOCKER: iptables v1.6.0: can't initialize iptables table `nat': Permission denied (you must be root)
Perhaps iptables or your kernel needs to be upgraded.
(exit status 3)
I'm a little stuck on where to go now as sudo isn't a thing on alpine.

Answer 1

Running the Docker daemon inside the Docker container is generally a dodgy prospect. We have this exact same requirement, and we solve it by mounting /var/run/docker.sock from the Docker host into the Docker container:
docker run -v /var/run/docker.sock:/var/run/docker.sock --privileged
That way the docker command inside the build agent container is actually talking to the Docker daemon on the host, not inside the container. Works really well for us.