The ops
library is a Python framework for developing and testing Kubernetes and machine charms. While charms can be written in any language, ops
defines the latest standard, and charmers are encouraged to use Python with ops
for all charms. The library is an official component of the Charm SDK, itself a part of the Juju universe.
ops
is available on PyPI.- The latest version of
ops
requires Python 3.8 or above.
Juju | Learn how to quickly deploy, integrate, and manage charms on any cloud with Juju. It's as simple as juju deploy foo , juju integrate foo bar , and so on -- on any cloud. |
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Charmhub | Sample our existing charms on Charmhub. A charm can be a cluster (OpenStack, Kubernetes), a data platform (PostgreSQL, MongoDB, etc.), an observability stack (Canonical Observability Stack), an MLOps solution (Kubeflow), and so much more. |
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👉 | Charm SDK | Write your own charm! Juju is written in Go, but our SDK supports easy charm development in Python. |
Let's use ops
to build a Kubernetes charm:
See Charm SDK | Set up an Ubuntu
charm-dev
VM with Multipass.
Choose the MicroK8s track.
On your Multipass VM, create a charm directory and use Charmcraft to initialise your charm file structure:
mkdir ops-example
cd ops-example
charmcraft init
This has created a standard charm directory structure:
$ ls -R
.:
CONTRIBUTING.md README.md pyproject.toml src tox.ini
LICENSE charmcraft.yaml requirements.txt tests
./src:
charm.py
./tests:
integration unit
./tests/integration:
test_charm.py
./tests/unit:
test_charm.py
Things to note:
-
The
charmcraft.yaml
file shows that what we have is an example charm calledops-example
, which uses an OCI image resourcehttpbin
fromkennethreitz/httpbin
. -
The
requirements.txt
file lists the version ofops
to use. -
The
src/charm.py
file importsops
and usesops
constructs to create a charm classOpsExampleCharm
, observe Juju events, and pair them to event handlers:
import ops
class OpsExampleCharm(ops.CharmBase):
"""Charm the service."""
def __init__(self, *args):
super().__init__(*args)
self.framework.observe(self.on['httpbin'].pebble_ready, self._on_httpbin_pebble_ready)
self.framework.observe(self.on.config_changed, self._on_config_changed)
def _on_httpbin_pebble_ready(self, event: ops.PebbleReadyEvent):
"""Define and start a workload using the Pebble API.
Change this example to suit your needs. You'll need to specify the right entrypoint and
environment configuration for your specific workload.
Learn more about interacting with Pebble at at https://juju.is/docs/sdk/pebble.
"""
# Get a reference the container attribute on the PebbleReadyEvent
container = event.workload
# Add initial Pebble config layer using the Pebble API
container.add_layer("httpbin", self._pebble_layer, combine=True)
# Make Pebble reevaluate its plan, ensuring any services are started if enabled.
container.replan()
# Learn more about statuses in the SDK docs:
# https://juju.is/docs/sdk/constructs#heading--statuses
self.unit.status = ops.ActiveStatus()
See more:
ops.PebbleReadyEvent
- The
tests/unit/test_charm.py
file importsops.testing
and uses it to set up a testing harness:
import ops.testing
class TestCharm(unittest.TestCase):
def setUp(self):
self.harness = ops.testing.Harness(OpsExampleCharm)
self.addCleanup(self.harness.cleanup)
self.harness.begin()
def test_httpbin_pebble_ready(self):
# Expected plan after Pebble ready with default config
expected_plan = {
"services": {
"httpbin": {
"override": "replace",
"summary": "httpbin",
"command": "gunicorn -b 0.0.0.0:80 httpbin:app -k gevent",
"startup": "enabled",
"environment": {"GUNICORN_CMD_ARGS": "--log-level info"},
}
},
}
# Simulate the container coming up and emission of pebble-ready event
self.harness.container_pebble_ready("httpbin")
# Get the plan now we've run PebbleReady
updated_plan = self.harness.get_container_pebble_plan("httpbin").to_dict()
# Check we've got the plan we expected
self.assertEqual(expected_plan, updated_plan)
# Check the service was started
service = self.harness.model.unit.get_container("httpbin").get_service("httpbin")
self.assertTrue(service.is_running())
# Ensure we set an ActiveStatus with no message
self.assertEqual(self.harness.model.unit.status, ops.ActiveStatus())
See more:
ops.testing.Harness
Explore further, start editing the files, or skip ahead and pack the charm:
charmcraft pack
If you didn't take any wrong turn or simply left the charm exactly as it was, this has created a file called ops-example_ubuntu-22.04-amd64.charm
(the architecture bit may be different depending on your system's architecture). Use this name and the resource from the metadata.yaml
to deploy your example charm to your local MicroK8s cloud:
juju deploy ./ops-example_ubuntu-22.04-amd64.charm --resource httpbin-image=kennethreitz/httpbin
Congratulations, you’ve just built your first Kubernetes charm using ops
!
See Charm SDK | Clean up.
- Read our user documentation, which includes other guides showing
ops
in action - Dig into the
ops
API reference
Read our Code of conduct and:
- Join our chat: Mattermost
- Join our forum: Discourse
- Report an
ops
bug using GitHub issues - Raise a general https://juju.is/docs documentation issue on GitHub | juju/docs
- Read our documentation contributor guidelines and help improve a doc
- Read our codebase contributor guidelines and help improve the codebase
- Write a charm and publish it on Charmhub