On a batch job, Am doing a large number of operations inside a docker.

Is there to send a command from inside so docker can come back as if it were just started ?

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2 Answers

You just need to install docker client when building your docker images and map /var/run/docker.sock when running a new container to enable docker client inside the container to connect the docker daemon on the host, then you can use docker command just like on the host.

First, add commands to install docker-ce in your Dockerfile:

FROM centos:7.8.2003
ENV DOCKER_VERSION='19.03.8'
RUN set -ex \ && DOCKER_FILENAME= \ && curl -L ${DOCKER_FILENAME} | tar -C /usr/bin/ -xzf - --strip-components 1 docker/docker

Then, build a new image and run a new container using it:

$ docker build --tag docker-in-docker:v1 .
$ docker run -dit \ --name docker-in-docker \ -v /var/run/docker.sock:/var/run/docker.sock:ro \ docker-in-docker:v1 bash

Now, you can operate docker-daemon (on the host) inside docker container.

$ docker exec -it docker-in-docker docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
bdc2d81b2227 docker-in-docker:v1 "bash" 8 seconds ago Up 7 seconds docker-in-docker
# just restart the container docker-in-docker in the container docker-in-docker:
$ docker exec docker-in-docker docker restart docker-in-docker

3

reboot command works from withing container. I use this in my Go code inside docker

out, err = exec.Command("reboot").Output()

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