Dockerizing all the things: Running Ansible inside Docker container

Automating things in software development is more than useful and using Ansible is one way to automate software provisioning, configuration management, and application deployment. Normally you would install Ansible to your control node just like any other application but an alternate strategy is to deploy Ansible inside a standalone Docker image. But why would you do that? This approach has benefits to i.a. operational processes.

Although Ansible does not require installation of any agents within managed nodes, the environment where Ansible is installed is not so simple to setup. In control node it requires specific Python libraries and their system dependencies. So instead of using package manager to install Ansible and it’s dependencies we just pull a Docker image.

By creating an Ansible Docker image you get the Ansible version you want and isolate all of the required dependencies from the host machine which potentially might break things in other areas. And to keep things small and clean your image uses Alpine Linux.

The Dockerfile is:

FROM alpine:3.6
 
ENV ANSIBLE_VERSION 2.3.0.0
 
ENV BUILD_PACKAGES \
  bash \
  curl \
  tar \
  openssh-client \
  git \
  python \
  py-boto \
  py-dateutil \
  py-httplib2 \
  py-jinja2 \
  py-paramiko \
  py-pip \
  py-setuptools \
  py-yaml \
  ca-certificates
 
RUN apk --update add --virtual build-dependencies \
  gcc \
  musl-dev \
  libffi-dev \
  openssl-dev \
  python-dev
 
RUN set -x && \
  apk update && apk upgrade && \
  apk add --no-cache ${BUILD_PACKAGES} && \
  pip install --upgrade pip && \
  pip install python-keyczar docker-py && \
  apk del build-dependencies && \
  rm -rf /var/cache/apk/*
 
RUN mkdir -p /etc/ansible/ /ansible
 
RUN echo "[local]" >> /etc/ansible/hosts && \
  echo "localhost" >> /etc/ansible/hosts
 
RUN curl -fsSL https://releases.ansible.com/ansible/ansible-${ANSIBLE_VERSION}.tar.gz -o ansible.tar.gz && \
  tar -xzf ansible.tar.gz -C /ansible --strip-components 1 && \
  rm -fr ansible.tar.gz /ansible/docs /ansible/examples /ansible/packaging
 
ENV ANSIBLE_GATHERING smart
ENV ANSIBLE_HOST_KEY_CHECKING false
ENV ANSIBLE_RETRY_FILES_ENABLED false
ENV ANSIBLE_ROLES_PATH /ansible/playbooks/roles
ENV ANSIBLE_SSH_PIPELINING True
ENV PYTHONPATH /ansible/lib
ENV PATH /ansible/bin:$PATH
ENV ANSIBLE_LIBRARY /ansible/library
 
WORKDIR /ansible/playbooks
 
ENTRYPOINT ["ansible-playbook"]

The Dockerfile declares an entrypoint enabling the running container to function as a self-contained executable, working as a proxy to the ansible-playbook command.

Build the image as:

docker build -t walokra/ansible-playbook .

The command for running ansible-playbook from inside the container, e.g.:

docker run --rm -it -v $(pwd):/ansible/playbooks \
    walokra/ansible-playbook site.yml

If Ansible is interacting with external machines, you’ll need to mount an SSH key pair for the duration of the play:

docker run --rm -it \
    -v ~/.ssh/id_rsa:/root/.ssh/id_rsa \
    -v ~/.ssh/id_rsa.pub:/root/.ssh/id_rsa.pub \
    -v $(pwd):/ansible/playbooks \
    walokra/ansible-playbook site.yml

To make things easier you can use shell script named ansible_helper that wraps a Docker image containing Ansible:

#!/usr/bin/env bash
docker run --rm -it \
  -v ~/.ssh/id_rsa:/root/.ssh/id_rsa \
  -v ~/.ssh/id_rsa.pub:/root/.ssh/id_rsa.pub \
  -v $(pwd):/ansible_playbooks \
  -v /var/log/ansible/ansible.log \
  walokra/ansible-playbook "$@"

Point the above script to any inventory file so that you can execute any Ansible command on any host, e.g.

./ansible_helper play playbooks/deploy.yml -i inventory/dev -e 'some_var=some_value'

Now we have dockerized Ansible, isolated it’s dependencies and are not restricted to some old version which we get from Linux distribution’s package manager. Crafty, isn’t it? Check the docker-ansible-playbook repository for more information and examples with Ansible Vault.

This blog post and Dockerfile borrows from Misiowiec’s post Running Ansible Inside Docker and his earlier work. If you want to test playbooks it’s work checking out his ansible_playbook repository. Since then Alpine Linux has evolved and things could be cleaned a bit more like getting Ansible directly from testing repository.