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| # The ops library | ||
| # The `ops` library | ||
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| <!-- The text below is also at the top of ops/__init__.py. Keep in sync! --> | ||
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| The ops library is a Python framework ([`available on PyPI`](https://pypi.org/project/ops/)) for developing | ||
| and testing [Juju](https://juju.is/) charms in a consistent way, using standard Python constructs | ||
| to allow for clean, maintainable, and reusable code. | ||
| The `ops` library is a Python framework for developing and testing Kubernetes and machine [charms](https://juju.is/docs/sdk/charmed-operators). 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](https://juju.is/). | ||
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| A charm is an operator -- business logic encapsulated in a reusable software | ||
| package that automates every aspect of an application's life. | ||
| > - `ops` is [available on PyPI](https://pypi.org/project/ops/). | ||
| > - The latest version of `ops` requires Python 3.8 or above. | ||
| Charms written with ops support Kubernetes using Juju's "sidecar charm" | ||
| pattern, as well as charms that deploy to Linux-based machines and containers. | ||
| |||| | ||
| |-|-|- | | ||
| || [Juju](https://juju.is/docs/juju) | Learn how to quickly deploy, integrate, and manage charms on any cloud with Juju. <br> _It's as simple as `juju deploy foo`, `juju integrate foo bar`, and so on -- on any cloud._ | | ||
| |||| | ||
| || [Charmhub](https://charmhub.io/) | Sample our existing charms on Charmhub. <br> _A charm can be a cluster ([OpenStack](https://charmhub.io/openstack-base), [Kubernetes](https://charmhub.io/charmed-kubernetes)), a data platform ([PostgreSQL](https://charmhub.io/postgresql-k8s), [MongoDB](https://charmhub.io/mongodb), etc.), an observability stack ([Canonical Observability Stack](https://charmhub.io/cos-lite)), an MLOps solution ([Kubeflow](https://charmhub.io/kubeflow)), and so much more._ | | ||
| |||| | ||
| |:point_right:| [Charm SDK](https://juju.is/docs/sdk) | Write your own charm! <br> _Juju is written in Go, but our SDK supports easy charm development in Python._ | | ||
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| Charms should do one thing and do it well. Each charm drives a single | ||
| application and can be integrated with other charms to deliver a complex | ||
| system. A charm handles creating the application in addition to scaling, | ||
| configuration, optimisation, networking, service mesh, observability, and other | ||
| day-2 operations specific to the application. | ||
| ## Give it a try | ||
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| The ops library is part of the Charm SDK (the other part being Charmcraft). | ||
| Full developer documentation for the Charm SDK is available at | ||
| https://juju.is/docs/sdk. | ||
| Let's use `ops` to build a Kubernetes charm: | ||
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| To learn more about Juju, visit https://juju.is/docs/olm. | ||
| ### Set up | ||
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| > See [Charm SDK | Set up an Ubuntu `charm-dev` VM with Multipass](https://juju.is/docs/sdk/dev-setup#heading--automatic-set-up-an-ubuntu-charm-dev-vm-with-multipass). <br> Choose the MicroK8s track. | ||
| ## Pure Python | ||
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| The framework provides a standardised Python object model that represents the | ||
| application graph, as well as an event-handling mechanism for distributed | ||
| system coordination and communication. | ||
| ### Write your charm | ||
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| The latest version of ops requires Python 3.8 or above. | ||
| On your Multipass VM, create a charm directory and use Charmcraft to initialise your charm file structure: | ||
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| Juju itself is written in Go for efficient concurrency even in large | ||
| deployments. Charms can be written in any language, however, we recommend using | ||
| Python with this framework to make development easier and more standardised. | ||
| All new charms at Canonical are written using it. | ||
| ```shell-script | ||
| mkdir ops-example | ||
| cd ops-example | ||
| charmcraft init | ||
| ``` | ||
| This has created a standard charm directory structure. Poke around. | ||
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| Things to note: | ||
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| - The `metadata.yaml` file shows that what we have is an example charm called `ops-example`, which uses an OCI image resource `httpbin` from `kennethreitz/httpbin`. | ||
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| ## Getting started | ||
| - The `requirements.txt` file lists the version of `ops` to use. | ||
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| A package of operator code is called a charmed operator or simply "charm". | ||
| You'll use [charmcraft](https://juju.is/docs/sdk/install-charmcraft) to | ||
| register your charm name and publish it when you are ready. You can follow one | ||
| of our [charming tutorials](https://juju.is/docs/sdk/tutorials) to get started | ||
| writing your first charm. | ||
| - The `src/charm.py` file imports `ops` and uses `ops` constructs to create a charm class `OpsExampleCharm`, observe Juju events, and pair them to event handlers: | ||
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| ```python | ||
| import ops | ||
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| class OpsExampleCharm(ops.CharmBase): | ||
| """Charm the service.""" | ||
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| 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) | ||
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| 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() | ||
| ``` | ||
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| ## Testing your charms | ||
| > See more: [`ops.PebbleReadyEvent`](https://ops.readthedocs.io/en/latest/index.html#ops.PebbleReadyEvent) | ||
| The framework provides a testing harness, so you can ensure that your charm | ||
| does the right thing in different scenarios, without having to create | ||
| a full deployment. Our [API documentation](https://ops.readthedocs.io/en/latest/#module-ops.testing) | ||
| has the details, including this example: | ||
| - The `tests/unit/test_charm.py` file imports `ops.testing` and uses it to set up a testing harness: | ||
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| ```python | ||
| import ops.testing | ||
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| class TestCharm(unittest.TestCase): | ||
| def test_foo(self): | ||
| harness = Harness(MyCharm) | ||
| self.addCleanup(harness.cleanup) # always clean up after ourselves | ||
| def setUp(self): | ||
| self.harness = ops.testing.Harness(OpsExampleCharm) | ||
| self.addCleanup(self.harness.cleanup) | ||
| self.harness.begin() | ||
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| 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()) | ||
| ``` | ||
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| # Instantiate the charm and trigger events that Juju would on startup | ||
| harness.begin_with_initial_hooks() | ||
| > See more: [`ops.testing.Harness`](https://ops.readthedocs.io/en/latest/#ops.testing.Harness) | ||
| # Update charm config and trigger config-changed | ||
| harness.update_config({'log_level': 'warn'}) | ||
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| # Check that charm properly handled config-changed, for example, | ||
| # the charm added the correct Pebble layer | ||
| plan = harness.get_container_pebble_plan('prometheus') | ||
| self.assertIn('--log.level=warn', plan.services['prometheus'].command) | ||
| Explore further, start editing the files, or skip ahead and pack the charm: | ||
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| ```shell-script | ||
| charmcraft pack | ||
| ``` | ||
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| 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: | ||
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| ```shell-script | ||
| juju deploy ./ops-example_ubuntu-22.04-amd64.charm --resource httpbin-image=kennethreitz/httpbin | ||
| ``` | ||
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| Congratulations, you’ve just built your first Kubernetes charm using `ops`! | ||
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| ### Clean up | ||
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| > See [Charm SDK | Clean up](https://juju.is/docs/sdk/dev-setup#heading--automatic-set-up-an-ubuntu-charm-dev-vm-with-multipass). | ||
| ## Talk to us | ||
| ## Next steps | ||
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| If you need help, have ideas, or would just like to chat with us, reach out on | ||
| the Charmhub [Mattermost]. | ||
| ### Learn more | ||
| - Read our [user documentation](https://juju.is/docs/sdk/ops), which includes other guides showing `ops` in action | ||
| - Dig into the [`ops` API reference](https://ops.readthedocs.io/en/latest/) | ||
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| We also pay attention to the Charmhub [Discourse]. | ||
| ### Chat with us | ||
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| And of course you can deep dive into the [API reference]. | ||
| Read our [Code of conduct](https://ubuntu.com/community/code-of-conduct) and: | ||
| - Join our chat: [Mattermost](https://chat.charmhub.io/charmhub/channels/ops) | ||
| - Join our forum: [Discourse](https://discourse.charmhub.io/) | ||
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| ### File an issue | ||
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| [Discourse]: https://discourse.charmhub.io/ | ||
| [API reference]: https://ops.readthedocs.io/ | ||
| [Mattermost]: https://chat.charmhub.io/charmhub/channels/charm-dev | ||
| - Report an `ops` bug using [GitHub issues](https://github.com/canonical/operator/issues) | ||
| - Raise a general https://juju.is/docs documentation issue on [GitHub | juju/docs](https://github.com/juju/docs) | ||
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| ### Make your mark | ||
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| ## Development of the framework | ||
| - Read our [documentation contributor guidelines](https://discourse.charmhub.io/t/documentation-guidelines-for-contributors/1245) and help improve a doc | ||
| - Read our [codebase contributor guidelines](HACKING.md) and help improve the codebase | ||
| - Write a charm and publish it on [Charmhub](https://charmhub.io/) | ||
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| See [HACKING.md](HACKING.md) for details on dev environments, testing, and so | ||
| on. |