Charmcraft is for Kubernetes operator developers

Charmcraft supports Kubernetes operator development.

Charmcraft enables collaboration between operator developers, and publication on Charmhub, home of the Open Operator Collection.

Use charmcraft to:

• Init a new charm file structure
• Build your operator into a charm for distribution
• Register your charm name on Charmhub
• Upload your charms to Charmhub
• Release your charms into channels

You can use charmcraft with operators written in any language but we recommend the Python Operator Framework on Github which is also on PyPI for ease of development and collaboration.

Charmcraft and the Python Operator Framework extend the operator pattern beyond Kubernetes with universal operators that drive Linux and Windows apps. The universal operator pattern is very exciting for multi-cloud application management.

Install

The easiest way to install charmcraft is with

sudo snap install charmcraft --beta

There are multiple channels other than --beta. See the full list with snap info charmcraft. We recommend either latest/stable or latest/beta for everyday charming. With the snap you will always be up to date as Charmhub services and APIs evolve.

You can also install from PyPI with pip3 install --user charmcraft

Initialize a charm operator package file structure

Use charmcraft init to create a new template charm operator file tree:

$ mkdir my-new-charm; cd my-new-charm
$ charmcraft init
All done.
There are some notes about things we think you should do.
These are marked with ‘TODO:’, as is customary. Namely:
      README.md: fill out the description
      README.md: explain how to use the charm
  metadata.yaml: fill out the charm's description
  metadata.yaml: fill out the charm's summary

You will now have all the essential files for a charmed operator, including the actual src/charm.py skeleton and various items of metadata. Charmcraft assumes you want to work in Python so it will add requirements.txt with the Python operator framework ops, and other conventional development support files.

Build your charm

With a correct metadata.yaml and with ops in requirements.txt you can build a charm with:

$ charmcraft build
Created 'test-charm.charm'.

charmcraft build will fetch additional files into the tree from PyPI based on requirements.txt and will compile modules using a virtualenv.

The charm is just a zipfile with metadata and the operator code itself:

$ unzip -l test-charm.charm
Archive:  test-charm.charm
  Length      Date    Time    Name
---------  ---------- -----   ----
      221  2020-11-15 08:10   metadata.yaml
[...]
    25304  2020-11-15 08:14   venv/yaml/__pycache__/scanner.cpython-38.pyc
---------                     -------
   812617                     84 files

Now, if you have a Kubernetes cluster with the Juju OLM accessible you can directly juju deploy <test-charm.charm> to the cluster. You do not need to publish your operator on Charmhub, you can pass the charm file around directly to users, or for CI/CD purposes.

Charmhub login and charm name reservations

Charmhub is the world's largest repository of operators. It makes it easy to share and collaborate on operators. The community are interested in operators for a very wide range of purposes, including infrastructure-as-code and legacy application management, and of course Kubernetes operators.

Use charmcraft login and charmcraft logout to sign into Charmhub.

Charmhub name registration

You can register operator names in Charmhub with charmcraft register <name>. Many common names have been reserved, you are encouraged to discuss your interest in leading or collaborating on a charm in Charmhub Discourse.

Charmhub naming policy is the principle of least surprise - a well-known name should map to an operator that most people would expect to get for that name.

Operators in Charmhub can be renamed as needed, so feel free to register a temporary name, such as - as a placeholder.

Operator upload and release

Charmhub operators are published in channels, like:

latest/stable
latest/candidate
latest/beta
latest/edge
1.3/beta
1.3/edge
1.2/stable
1.2/candidate
1.0/stable

Use charmcraft upload to get a new revision number for your freshly built charm, and charmcraft release to release a revision into any particular channel for your users.

Charmcraft source

Get the source from github with:

git clone https://github.com/canonical/charmcraft.git
cd charmcraft
virtualenv venv
. venv/bin/activate
pip install -r requirements.txt
python -m charmcraft

If you would like to run the tests you can do so with

pip install -r requirements-dev.txt
./run_tests

Contributions welcome!