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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.
Contents
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 (with slight wording improvements):
--- - 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 configured 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 is correct 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
This section focuses on the user context, when using virt_net. The purpose is to understand the workflow of the user. It is insufficient to just look at libvirt network features.
An Ansible developer wants to run a virtual machine as staging environment for her Ansible configuration. Could be a network of several virtual machines. Mainly, I assume the virtual machine runs on the local host in the user space.
Basic steps:
- Boot up a fresh virtual machine from a fresh image
- Bootstrap Ansible playbook
- Test everything
- Clean up in the end
As part of the first step, we must ensure the virtual staging network is set up as needed.
--- - 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 (see parameter name). 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
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.
Testing systems in a continuous integration environment is basically the next step after the previous use case. The CI system might select the right test machine bootstrap the virtual machine, run test case and clean up everything in the end. Ansible can help to create the virtual machine as well as to deploy the current software in the virtual machine. Note: I think libvirt might be good for small setups. For bigger setups we have usual other suspects like OKD, OpenStack etc.
The Ansible playbook is very similar to the previous use case: non-persistent setup (everything managed by Ansible), but no local host.
--- - name: Ensure the test environment is set up correctly hosts: {{ staging_host }} 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
Run a service XY in a virtual machine. Again this is for small environments. The host could be selected by the infrastructure file or by a simple management component. In this case, we would configure the autostart option.
--- - 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
Similar modules are
- OpenStack subnet module
- VMware guest module
- Kubernetes module
- Docker network module, Docker container module and Docker compose module
TODO ...
TODO ...
To simplify the definition, we could distinguish between
- mandatory parameters (no simplification)
- parameters with default values
- optional parameters without default values that remain untouched.
Parameter | Default value |
---|---|
persistent | no |
active | yes |
autostart | no |
uri | qemu:///system |
TODO ...
Persistent | Active | State name |
---|---|---|
yes | yes | |
yes | no | |
no | yes | |
no | no |
TODO ...
We can distinguish four machines to bootstrap a virtual machine with Ansible.
- Machine that executes the playbook
- Machine on which the libvirt client runs
- Machine the libvirt client connects to
- Instantiated and booted virtual machine that needs to be set up via Ansible
TODO ...
TODO ...
Do we need the commands info, facts, get_xml, status and net_list all together?
From VMware module: "Note that this play disables the gather_facts parameter, since you don’t want to collect facts about localhost."
TODO ...
TODO ...
This Wiki is used for quick notes, not for support or documentation.
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