trents_blog/docs/posts/ansible-kvm-router-lab-part-3.md

---
title: "Ansible KVM Router Lab Part 3"
date: 2021-10-16
draft: false
tags: ["linux", "kvm", "libvirt", "virsh", "ansible", "bash"]
authors: ["trent"]
post: 28
---
date: 2021-10-16

## Introduction
This is Part 3 of a multi-part series of blog posts for building a
[router lab](https://github.com/TrentSPalmer/router-lab){target="_blank"}
automatically using a series of bash scripts and ansible.

[Ansible KVM Router Lab Part 1](/posts/ansible-kvm-router-lab-part-1/){target="_blank"}
is an overview.

In [Ansible KVM Router Lab Part 2](/posts/ansible-kvm-router-lab-part-2/){target="_blank"},
I break down the script 
[build_vms.bash](https://github.com/TrentSPalmer/router-lab/blob/master/build_vms.bash){target="_blank"}.

In this post I explain
[define_bridge_networks.bash](https://github.com/TrentSPalmer/router-lab/blob/master/define_bridge_networks.bash){target="_blank"}
and
[shutdown_vms.bash](https://github.com/TrentSPalmer/router-lab/blob/master/shutdown_vms.bash){target="_blank"}
scripts which are used to construct the lab.

In [Ansible KVM Router Lab Part 4](/posts/ansible-kvm-router-lab-part-4/){target="_blank"},
I explain
[connect_vms_to_bridges.bash](https://github.com/TrentSPalmer/router-lab/blob/master/connect_vms_to_bridges.bash){target="_blank"},
[start_vms.bash](https://github.com/TrentSPalmer/router-lab/blob/master/start_vms.bash){target="_blank"},
and [rebuild_known_hosts.bash](https://github.com/TrentSPalmer/router-lab/blob/master/rebuild_known_hosts.bash){target="_blank"}
scripts which are used to construct the lab.

In [Ansible KVM Router Lab Part 5](/posts/ansible-kvm-router-lab-part-5/){target="_blank"},
I explain the ansible playbook tasks used to finish building the lab.

In [Ansible KVM Router Lab Part 6](/posts/ansible-kvm-router-lab-part-6/){target="_blank"},
I explain
[disconnect_vms_from_bridges.bash](https://github.com/TrentSPalmer/router-lab/blob/master/disconnect_vms_from_bridges.bash){target="_blank"},
[undefine_and_remove_vms.bash](https://github.com/TrentSPalmer/router-lab/blob/master/undefine_and_remove_vms.bash){target="_blank"},
and [remove_bridge_networks](https://github.com/TrentSPalmer/router-lab/blob/master/remove_bridge_networks.bash){target="_blank"}
which are used to destroy the lab.

## `define_bridge_networks.bash`
The router-lab has two bridge networks, in addition to the initial out-of-band
network which is used to contact the virtual machines directly.

### `check_uid "${USER_UID}"`
[define_bridge_networks.bash](https://github.com/TrentSPalmer/router-lab/blob/master/define_bridge_networks.bash)
begins by making sure that it is run as a _non-privileged_ user. You can call
the script with `bash define_bridge_networks.bash`.

### `function define_bridge_networks()`
`define_bridge_networks` calls `define_bridge_network` twice, once for each of the
upper bridge and the lower bridge. `define_bridge_network` parses the output of
`virsh net-list --all` to determine if the network is defined yet.  If not,
`virsh net-define vm_router_lab_lower_bridge.xml` or
`virsh net-define vm_router_lab_upper_bridge.xml` are invoked as necessary.
`define_bridge_network` then recursively calls itself for confirmation.

Links for
[vm_router_lab_upper_bridge.xml](https://github.com/TrentSPalmer/router-lab/blob/master/vm_router_lab_upper_bridge.xml){target="_blank"}
and
[vm_router_lab_lower_bridge.xml](https://github.com/TrentSPalmer/router-lab/blob/master/vm_router_lab_lower_bridge.xml){target="_blank"}.

### `function start_bridge_networks()`
`start_bridge_networks` calls `start_bridge_network` twice, once for each of the
upper and the lower bridge. `start_bridge_network` in turn parses the output of
`virsh net-info vm_router_lab_upper_bridge` and/or `virsh net-info vm_router_lab_lower_bridge`
to determine if the cooresponding network is running, and if not invokes
`virsh net-start vm_router_lab_upper_bridge` or `virsh net-start vm_router_lab_lower_bridge`,
and then recursively calls itself again for confirmation.

### `function autostart_bridge_networks()`
`autostart_bridge_networks` is nearly identical to `start_bridge_networks`, but
`virsh net-autostart vm_router_lab_upper_bridge` or `virsh net-autostart vm_router_lab_lower_bridge`,
are invoked in order to mark the cooresponding network to autostart.

## `shutdown_vms.bash`
After creating the upper and lower bridge networks, it is necessary to shut down
the lab clients before connecting the lab clients to the bridge networks. This is
because network interfaces must be _permanently_ added to the lab client definitions.

### `check_uid "${USER_UID}"`
[shutdown_vms.bash](https://github.com/TrentSPalmer/router-lab/blob/master/shutdown_vms.bash)
begins by making sure that it is run as a _non-privileged_ user. You can call
the script with `bash shutdown_vms.bash`.

### `function shutdown_vms()`
`shutdown_vms` simultaneously calls `shutdown_vm` on the entire MACHINES array.
`shutdown_vm` in turn parses the output of `virsh list --state-running` to determine if
the virtual machine is running, and if so invokes `virsh shutdown <vm>`. `shutdown_vm`
then recursively calls itself to confirm that the virtual machine is indeed shut down.

## To Be Continued
In [Ansible KVM Router Lab Part 4](/posts/ansible-kvm-router-lab-part-4/){target="_blank"},
I explain
[connect_vms_to_bridges.bash](https://github.com/TrentSPalmer/router-lab/blob/master/connect_vms_to_bridges.bash){target="_blank"},
[start_vms.bash](https://github.com/TrentSPalmer/router-lab/blob/master/start_vms.bash){target="_blank"},
and
[rebuild_known_hosts.bash](https://github.com/TrentSPalmer/router-lab/blob/master/rebuild_known_hosts.bash){target="_blank"}
scripts which are used to construct the lab.