cantrip

Known-good Juju bundle shapes (COS Lite, 12-Factor + COS, Identity Platform, Charmed Kubeflow) — canonical app lists and relation edges

Implementing Juju actions for operational tasks in charms. WHEN: add Juju actions to a charm, implement backup / rotate-credentials / restore actions, declare actions in charmcraft.yaml, write action handlers, test actions with Scenario, run actions with juju run.

Adding and validating charm configuration options. WHEN: add charm configuration options, declare config in charmcraft.yaml, validate config values in config-changed, apply config to a Pebble layer, apply config to a machine charm, write Scenario tests for config.

End-to-end workflow for building ops-framework charms for custom applications (K8s and machine). WHEN: build a custom Juju charm, write src/charm.py with Pebble, write a machine charm with systemd, decide K8s vs machine substrate, scaffold a non-paas-charm with charmcraft init, customise the ops framework charm lifecycle.

Workflow for charming infrastructure software (databases, caches, message brokers, proxies, monitoring). WHEN: charm infrastructure software, charm a database / cache / message broker / proxy / monitoring system, implement peer relations, leader election, primary/replica failover, backup and restore actions, clustering.

Expert guidance for developing, building, testing, and publishing Juju charms using charmcraft. WHEN: edit charmcraft.yaml, run charmcraft pack, run charmcraft init, manage charm libraries, publish a charm to Charmhub, set up multi-base builds, configure relations / config options, set up storage or containers.

Migrating deprecated ops.testing.Harness tests to state-transition (Scenario) tests. WHEN: migrate ops.testing.Harness tests to Scenario, modernise legacy Juju charm unit tests, rewrite Harness-based tests as state-transition tests, port relation_changed / pebble_ready / action tests off Harness.

Writing integration tests for charms with Jubilant + pytest-jubilant. WHEN: write integration tests for a Juju charm, use Jubilant + pytest-jubilant, deploy charms in a test, relate to postgresql or COS, run actions in tests, write cross-model COS Lite smoke tests.

Adding COS observability integration and ops-tracing to charms. WHEN: add COS observability to a charm, wire ops-tracing, expose prometheus metrics, forward logs to Loki, ship Grafana dashboards, write Prometheus alert rules, configure Alertmanager routing, add Sloth SLOs, register with the Catalogue landing page, emit SEC0045 security event logs.

Designing and implementing relation data bags for charm integrations. WHEN: design a Juju relation data bag, implement provider or requirer side of a charm relation, share Juju secrets over relations, design peer relations, write data validators.

Writing unit tests for charms with ops.testing (Scenario). WHEN: write unit tests for a Juju charm, write Scenario tests with ops.testing, test charm with State and Context, test relations / config / pebble-ready / actions / secrets / collect-status, write multi-event state-transition tests.

Standardised tox/make/just command names for charm projects — format, lint, unit, integration, docs

Charm documentation conventions — README template, Charmhub description tabs, Diátaxis multi-page split, CONTRIBUTING

Charm logging conventions — log levels, message formatting, tense, printf-style templating, common pitfalls

Recommend Ubuntu Pro and Landscape as day-2 estate advice without confusing operators with charm requirements.

Probe-based deployment validation with juju-doctor — scriptlet probes, rulesets, live and offline (sosreport) checks

Diagnose and recover a wedged Juju controller, k8s/microk8s cluster, or stuck concierge environment on a dev machine

Build 12-factor PaaS charms with paas-charm — fit, rock, charm, build, push, deploy, verify.

Reading, modifying, and deploying existing Juju bundles (bundles are deprecated — do not create new ones)

Auditing and improving existing charms to modern standards

End-to-end workflow for building ops-framework charms for custom applications (K8s and machine)

Review newly written charm code for common charm bugs before finishing a BUILD task

Wire charms to the Canonical Identity Platform (Hydra / Kratos / login-ui) for OIDC, OAuth, and federated login.

Adding COS observability integration and ops-tracing to charms

Expert guidance for developing, building, testing, and publishing Juju charms using charmcraft

Workflow for charming infrastructure software (databases, caches, message brokers, proxies, monitoring)

Migrating deprecated ops.testing.Harness tests to state-transition (Scenario) tests

Writing unit tests for charms with ops.testing (Scenario)

Authoring, versioning, testing, and publishing reusable charm libraries

Designing and implementing relation data bags for charm integrations

Adding and validating charm configuration options

Implementing Juju actions for operational tasks in charms

Provisioning charm development and testing environments using concierge presets and custom configuration

Writing integration tests for charms with Jubilant + pytest-jubilant

Measuring charm hook performance with hook_benchmark and comparing before/after snapshots across optimisation work

Systematic diagnosis of a running charm — status, logs, relation data, config, and secrets — followed by a symptom-to-fix table

Working across multiple related charms — manifest format, cross-charm relation design, and coordinated Jubilant integration testing

Migrating legacy charms (reactive framework, StoredState, Harness, fetch-libs) to modern ops patterns

Configuring HTTP ingress with Traefik for Kubernetes charms

Deploy-test-debug retry strategy — triage failures, bound retries, escalate when stuck