Ideas virt_net

Everything started with issues with the virt_net modules:

• ansible-collections/community.libvirt#38
• ansible-collections/community.libvirt#46
• ansible-collections/community.libvirt#47

This page collects ideas for dicussion to find the right way of a fix / improvement.

General paradigm

From Ansible use case configuration management:

Ansible features an state-driven resource model that describes the desired state of computer systems and services, not the paths to get them to this state. No matter what state a system is in, Ansible understands how to transform it to the desired state (and also supports a "dry run" mode to preview needed changes). This allows reliable and repeatable IT infrastructure configuration, avoiding the potential failures from scripting and script-based solutions that describe explicit and often irreversible actions rather than the end goal."

Good example from https://hvops.com/articles/ansible-vs-shell-scripts/:

---
- hosts: all
  tasks:

  - name: Ensure the PGP key is installed
    apt_key: >
      state=present
      id=AC40B2F7
      url="http://keyserver.ubuntu.com/pks/lookup?op=get&fingerprint=on&search=0x561F9B9CAC40B2F7"

  - name: Ensure https support for apt is installed
    apt: >
      state=present
      pkg=apt-transport-https

  - name: Ensure the passenger apt repository is added
    apt_repository: >
      state=present
      repo='deb https://oss-binaries.phusionpassenger.com/apt/passenger raring main'

  - name: Ensure nginx is installed
    apt: >
      state=present
      pkg=nginx-full

  - name: Ensure passenger is installed
    apt: >
      state=present
      pkg=passenger
      update_cache=yes

  - name: Ensure the nginx configuration file is set
    copy: >
      src=/app/config/nginx.conf
      dest=/etc/nginx/nginx.conf

  - name: Ensure nginx is running
    service: >
      name=nginx
      state=started

Some critical / skeptical words: https://regebro.wordpress.com/2014/09/17/a-script-is-not-configuration/

Operational scenarios and usage examples

I want to focus on virt_net, but sometimes I will draw a parallel with the domains.

Developer using a virtual machine for testing on her own machine

An Ansible developer wants to run a virtual machine as staging environment. Could be a network of several virtual machines.

Basic steps:

1. Boot up a fresh virtual machine from a fresh image
2. Bootstrap Ansible playbook
3. Test everything
4. Clean up in the end

As part of the first step, we must ensure the virtual staging network is set up as needed.

Example: Adapt the default network

---
- name: Ensure the test environment is set up correctly
  hosts: localhost
  tasks:
    - name: Ensure the default network defined correctly and running
      community.libvirt.virt_net:
        xml: '{{ lookup("template", "network_default.xml") }}'
        persistent: yes
        active: yes

I do not define parameters here, which are already part of the XML template. Especially I avoided the parameter name in the example to see how it feels. The combination of name and xml has issues in the current implementation. However, the default network already exists. The user needs not specify an XML definition, if she is happy with the default definition of libvirt. In this case, she needs a parameter name.

---
- name: Ensure the test environment is set up correctly
  hosts: localhost
  tasks:
    - name: Ensure the default network is running
      community.libvirt.virt_net:
        name: default
        active: yes

Example: Additional network

This network can be non-persistent

---
- name: Ensure the test environment is set up correctly
  hosts: localhost
  tasks:
    - name: Ensure the network *development* is defined correctly and running
      community.libvirt.virt_net:
        xml: '{{ lookup("template", "network_development.xml") }}'
        persistent: no
        active: yes

After running the tests, the developer could clean up the development environment.

---
- name: Ensure a cleaned up development environment
  hosts: localhost
  tasks:
    - name: Ensure the network *development* is removed
      community.libvirt.virt_net:
        name: development
        persistent: no
        active: no

Having the parameter name sometimes in and out makes it a bit difficult, to bring the corresponding definitions together, if there are several network definitions.

Run a service in a virtual machine on a dedicated host

---
- name: Ensure the service XY is running
  hosts: all
  tasks:
    - name: Ensure the network *storage* is defined correctly and running
      community.libvirt.virt_net:
        xml: '{{ lookup("template", "network_storage.xml") }}'
        persistent: yes
        active: yes
        autostart: yes