Microsoft Azure Devops – Dynamic Docker Agent (Ansible)

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Often you may require a unique custom build/release agent with a specific set of tools.

A good example is a dynamic Ansible Agent that can manage post deployment configuration. This ensures configuration drift is minimised.

Secondly this part of a release is not too critical, so we can afford to spend a bit of time downloading a docker image if it is not already cached.

This article demonstates how you can dynamically spawn a docker container during your release pipeline to apply configuration leveraging Ansible. It will also demonstrate how to use Ansible Dynamic Inventory to detect Azure Virtual machine scale set instances – in the past you would run hacks on facter.

Prerequsites

You will require:

  • A docker image with ansible – You can use mine as a starting point – https://github.com/Romiko/DockerUbuntuDev
    The above is hosted at: dockerhub – romiko/ansible:latest (See reference at bottom of this page)
  • A Self-host Azure Devops Agent – Linux
  • Docker installed on the self-hosted agent
  • Docker configured to expose Docker Socket
    docker run -v /var/run/docker.sock:/var/run/docker.sock -d –name some_container some_image

Release Pipeline

Configure a CLI Task in your release pipeline.

variables:
  env: 'dev'

steps:
- task: AzureCLI@2
  displayName: 'Azure CLI Ansible'
  inputs:
    azureSubscription: 'RangerRom'
    scriptType: bash
    scriptLocation: inlineScript
    inlineScript: |
     set -x
     
     docker run --rm -v $(System.DefaultWorkingDirectory)/myproject/config:/playbooks/ romiko/ansible:latest \
      "cd  /playbooks/ansible; ansible-playbook --version; az login --service-principal --username $servicePrincipalId --password $servicePrincipalKey --tenant $tenantId; az account set --subscription $subscription;ansible-playbook my-playbook.yaml -i inventory_$(env)_azure_rm.yml --extra-vars \"ansible_ssh_pass=$(clientpassword)\""
    addSpnToEnvironment: true
    workingDirectory: '$(System.DefaultWorkingDirectory)/myproject/config/ansible'

In the above the code that is causing a SIBLING container to spawn on the self-hosted devops agent is:

docker run –rm -v $(System.DefaultWorkingDirectory)/myproject/config:/playbooks/ romiko/ansible:latest \ <command to execute inside the container>

Here we have a mount point occuring where the config folder in the repo will be mounted into the docker container.

-v <SourceFolder>:<MountPointInDockerContainer>

The rest of the code after the \ will execute on the docker container. So in the above,

  • The container will become a sibling,
  • Entry into a bash shell
  • Container will mount a /playbooks folder containing the source code from the build artifacts
  • Connect to azure
  • Run an anisble playbook.
  • The playbook will find all virtual machine scale sets in a resoruce group with a name pattern
  • Apply a configuration by configuring logstash to auto reload config files when they change
  • Apply a configuration by copying files

Ansible

The above is used to deploy configurations to an Azure Virtual Machine Scale Set. Ansible has a feature called dynamica inventory. We will leverage this feature to detect all active nodes/instances in a VMSS.

The structure of ansible is as follows:

Ansible Dynamic Inventory

So lets see how ansible can be used to detect all running instances in an Azure Virtual machine Scale Set

inventory_dev_azure_rm.yml

Below it will detect any VMSS cluster in resourcegroup rom-dev-elk-stack that has logstash in the name

plugin: azure_rm

include_vmss_resource_groups:
- rom-dev-elk-stack

conditional_groups:
  logstash_hosts: "'logstash' in name"

auth_source: auto

logstash_hosts.yml (Ensure this lives in a group_vars folder)

Now, I can configure ssh using a username or ssh keys.

---
ansible_connection: ssh
ansible_ssh_user: logstash

logstash-playbook.yaml

Below I now have ansible doing some configuration checks for me on a logstash pipeline (upstream/downstream architecture).


    - name: Logstash auto reloads check interval
      lineinfile:
        path: /etc/logstash/logstash.yml
        regexp: '^config\.reload\.interval'
        line: "config.reload.interval: 30s"
      become: true
      notify:
        - restart_service

    - name: Copy pipeline configs
      copy:
        src: ../pipelines/conf.d/
        dest: /etc/logstash/conf.d/
        owner: logstash
        group: logstash
      become: true
    
    - name: Copy pipeline settings
      copy:
        src: ../pipelines/register/
        dest: /etc/logstash/
        owner: logstash
        group: logstash
      become: true

To improve security – replace user/password ansible login with an SSH key pair.

References

To read up more about Docker Socket mount points. Check out

https://www.develves.net/blogs/asd/2016-05-27-alternative-to-docker-in-docker/

https://docs.ansible.com/ansible/latest/user_guide/intro_dynamic_inventory.html

Thanks to Shawn Wang and Ducas Francis for the inspirations on Docker Socket.

https://azure.microsoft.com/en-au/services/devops/

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