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getting-started-vm-charms.md

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Getting started (vm-charms)

Lets get started with charming vm charms on lxd.

What you’ll need:

  • Familiarity with the Juju OLM 1
  • Some Python programming language, Object-Oriented Programming, Event Handlers
  • Some basic LXD skill.

What you’ll learn:

Setup your local lxd cloud

First, make sure your iptables isn't going to mess up from docker fucking up your firewall.

iptables -P FORWARD ACCEPT; iptables -F FORWARD

Launch up a VM with 15GB disk on a Ubuntu 22.04. You can use other virtual machine managers (multipass, libvirt etc.) but I use lxd.

lxc launch ubuntu:jammy juj -d root,size=15GiB --vm

Setup the machine for the tutorial

lxc shell juj
root@juj:~# sudo echo Acquire::ForceIPv4 "true"; > /etc/apt/apt.conf.d/99force-ipv4
root@juj:~# sudo snap install juju --classic
root@juj:~# sudo snap install charmcraft --classic
root@juj:~# lxd init --auto
root@juj:~# lxc remote list
root@juj:~# juju bootstrap localhost tutorial-controller
Creating Juju controller "tutorial-controller" on localhost/localhost
Looking for packaged Juju agent version 2.9.38 for amd64
Located Juju agent version 2.9.38-ubuntu-amd64 at https://streams.canonical.com/juju/tools/agent/2.9.38/juju-2.9.38-linux-amd64.tgz
To configure your system to better support LXD containers, please see: https://linuxcontainers.org/lxd/docs/master/explanation/performance_tuning/
Launching controller instance(s) on localhost/localhost...
 - juju-3a5da3-0 (arch=amd64)                 
Installing Juju agent on bootstrap instance
Fetching Juju Dashboard 0.8.1
Waiting for address
Attempting to connect to fd42:e802:396b:494a:216:3eff:fe4b:8fc7:22
Attempting to connect to 10.77.114.74:22
Connected to fd42:e802:396b:494a:216:3eff:fe4b:8fc7
Running machine configuration script...
Bootstrap agent now started
Contacting Juju controller at 10.77.114.74 to verify accessibility...
Bootstrap complete, controller "tutorial-controller" is now available
Controller machines are in the "controller" model
Initial model "default" added

root@juj:~# juju status
Model    Controller           Cloud/Region         Version  SLA          Timestamp
default  tutorial-controller  localhost/localhost  2.9.38   unsupported  15:26:30Z

Model "admin/default" is empty.

Build a charm

Now when we have a juju controller atteched to a local cloud, lets get the charm initialized with charmcraft.

Initialize the charm

An empty directory with the name of our charm.

root@juj:~# mkdir mycharm
root@juj:~# cd mycharm
root@juj:~/mycharm# charmcraft init --profile machine # can be simple, machine or kubernetes

Edit the metadata.yaml and add the name to the charm.

vi metadata.yaml

Now, compile/pack the charm with charmcraft.

root@juj:~/mycharm# charmcraft pack # This takes a long time the first time (3-5 minutes) since it builds inside a full container.
Packing the charm                                                                                                                                                                    
Created 'mycharm_ubuntu-22.04amd64.charm'.                                                                                                                                          
Charms packed:                                                                                                                                                                       
   mycharm_ubuntu-22.04-amd64.charm

The charm is ready to be deployed. Later on, you would be able to upload it to charmhub, but thats another tutorial.

Deploy your charm on you local LXD cloud

juju deploy ./mycharm_ubuntu-22.04-amd64.charm

Next steps

    Add charm relations and interfaces
      - Example: https://github.com/erik78se/juju-operators-examples/tree/main/haproxy-relate
    Connect external charm libraries and interact with them:
      - Example: Missing
    Add charm actions: 
      - Example: https://github.com/erik78se/juju-operators-examples/tree/main/action-charm
    Add charm configurations: 
      - Example: Missing
    Write tests
      - Example: Missing

What happens with a charm after deploy?

This explains what happens to a charm once you deploy it and how you can implement advanced features for your charm, depending on your ambitions and needs for your charm and software. https://discourse.charmhub.io/t/a-charms-life/5938

More advanced topics

https://discourse.charmhub.io/t/talking-to-a-workload-control-flow-from-a-to-z/6161

Examples

https://github.com/erik78se/juju-operators-example