Docker with amazonlinux

Question

Complete newbie with Docker, but the concepts are sticking.

Goal

Create a container locally that matches my prod EC2 instance. Upgrade PHP7 and test my application.

Approach

My first step was to create just a basic box amazon linux box. Mount it and run the commands from the CLI. Then I can slowly build up the commands to put in my Dockerfile.

Problem

I build the box fine run yum update -Y and see the updates. However, when I run docker ps the image isn't listed? So I can't mount it. My composerfile is as follows...

FROM amazonlinux:2017.03

RUN yum update -y

Why is the box not remaining in an open state?

Answer 1

I had the same goal of testing instances in development environment and initially I thought it should be as easy as docker run amazonlinux:2 -it. But I was so wrong and it took me almost one full day to get it to work!

Funny thing is when you google "amazonlinux Docker" it's often people trying to install "Docker in amazonlinux", but here we want to install "amazonlinux in Docker"!

We also want to install Docker in that amazonlinux, so basically "Docker in amazonlinux in Docker" which is "Docker in Docker" eventually! ;D*

My findings:

• Amazonlinux in Docker (created via FROM amazonlinux:2) is so bare and empty that it doesn't even have basic stuffs like sudo or passwd.) New AWS EC2 instances do.
• In order to have your serviced properly working (to start any daemon, including Docker Daemon), you need to have /usr/sbin/init be there (via yum install initscripts and actually called. However, the meat you want to play with need your shell to start from /bin/bash.
• You are running a Docker within a Docker. That needs to be priviledged from the host in your docker run via --priviledged.
• You need to share the /sys/fs/cgroup from your host machine (it can be read-only) for it to be able to properly initialize docker daemon.

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My solution:

1) To fulfill the first two issues above, your Dockerfile can be:

FROM amazonlinux:2

RUN yum update -y && yum install -y initscripts;

CMD ["/usr/sbin/init"]

2) Build an image from it, e.g. docker build . -t ax1

3) Then, to address the latter two issues above, run a detached (running in background) container from it, priviledged, with a shared volume to your /sys/fs/cgroup. e.g.

docker run --name ac11 -d --privileged -v /sys/fs/cgroup:/sys/fs/cgroup:ro ax1

4) Finally you can bash into it using docker exec -it ac11 bash

5) Now, it's very close to a new EC2 instance. (Yet, missing sudo, actual ec2-user and other stuffs that we skipped in our Dockerfile to keep this solution simple.)

Anyway, now you can install docker as instructed by AWS Docs. That is, once you are in the container, do:

amazon-linux-extras install -y docker;

and then restart the docker service once:

service docker restart;

Now, docker ps should be working!