Charm maturity > Stage 2: Important capabilities
Your charm looks right, right enough for you to share it with the world. What next? Time to make sure it also works right! This document spells out the second round of standards that you should try to meet – standards designed to ensure that your charm is good enough to be used in production, at least for some use cases.
Assuming you’ve already published your charm on Charmhub, and passed the review to have it publicly listed, these standards are the way to ensure that your charm gains recognition as a noteworthy charm.
These standards keep evolving. Revisit this doc to get the latest updates.
Contents:
- The charm has sensible defaults
- The charm is compatible with the ecosystem
- The charm upgrades the application safely
- The charm scales up and down
- The charm is integrated with observability
The charm has sensible defaults
A user can deploy the charm with a sensible default configuration.
| Objectives | Tips, examples, further reading |
|---|---|
| The purpose is to provide a fast and reliable entry point for evaluation. Of course, optimised deployments will require configurations. | Often applications require initial passwords to be set, which should be auto-generated and retrievable using an action or Juju Secrets once available. Hostnames and load balancer addresses are examples that often cannot be set with a sensible default. But they should be covered in the documentation and indicated clearly in the status messages on deployment when not properly set. |
The charm is compatible with the ecosystem
The charm can expose provides/requires interfaces for integration ready to be adopted by the ecosystem.
| Objectives | Tips, examples, further reading |
|---|---|
| Newly proposed relations have been reviewed and approved by experts to ensure: • The relation is ready for adoption by other charmers from a development best practice point of view. • No conflicts with existing relations of published charms. • Relation naming and structuring are consistent with existing relations. • Tests cover integration with the applications consuming the relations. |
A Github project structures and defines the implementation of relations. No new relation should conflict with the ones covered by the relation integration set published on Github. |
The charm upgrades the application safely
The charm supports upgrading the workload and the application. An upgrade task preserves data and settings of both.
| Objectives | Tips, examples, further reading |
|---|---|
| A best practice is to support upgrades sequentially, meaning that users of the charm can regularly apply upgrades in the sequence of released revisions. | • How to upgrade applications with Juju |
The charm supports scaling up and down
If the application permits or supports it, the charm does not only scale up but also supports scaling down.| Objectives | Tips, examples, further reading |
|---|---|
| Scale-up and scale-down can involve the number of deployment units and the allocated resources (such as storage or computing). |
• Scaling applications with Juju Note that the cited links also point to how to deal with relations when instances are added or removed: |
The charm is integrated with observability
Engineers and administrators who operate an application at a production-grade level need to capture and interpret the application’s state.
| Objectives | Tips, examples, further reading |
|---|---|
| Integrating observability refers to providing: • a metrics endpoint, • alert rules, • Grafana dashboards, and • integration with a log sink (e.g. Loki). |
Consider the Canonical Observability Stack (COS) for covering observability in charms. Several endpoints are available from the COS to integrate with charms: • Provide metrics endpoints using the MetricsProviderEndpoint • Provide alert rules to Prometheus • Provide dashboards using the GrafanaDashboardProvider • Require a logging endpoint using the LogProxyConsumer or LokiPushApiConsumer More information is available on the Canonical Observability Stack homepage. Consider the zinc charm implementation as an example for integrations with Prometheus, Grafana and Loki. |