Lifecycle Events

Juju events allow progression of the charm in its lifecycle and encapsulates part of the execution context of a charm. Below is the list of observed events for wordpress-k8s charm with how the charm reacts to the event. For more information about the charm’s lifecycle in general, refer to the charm’s life documentation.

start

This event marks the charm’s state as started. The charm’s running state must be persisted by the charm in its own state. See the documentation on the start event.

uploads_storage_attached

This event marks the charm’s storage availability. The name of the event derived from the name of the storage noted in the metadata.yaml configuration under “storage” key. containers.wordpress.mounts.storage and storage.uploads section. The storage filesystem maps to /var/www/html/wp-content/uploads directory of the WordPress application, which is used to store uploaded content from the WordPress user.

leader_elected

This event is fired when juju elects a leader unit among the replica peers. Wordpress-k8s charm then responds by setting up secrets and sharing them with peers through peer relation databag if not already set.

config-changed

WordPress-k8s charm reacts to any configuration change and runs reconciliation between the current state and the desired state. See the list of configurations.

wordpress_pebble_ready

When this event is fired, wordpress-k8s charm installs, configures and starts Apache server for WordPress through pebble if the storage is available. Configurations that are set dynamically include database connection and secrets used by the WordPress application. Dynamic configurations are modified in wp-config.php file and the changes are pushed through pebble.

apache_prometheus_exporter_pebble_ready

This event signals that the apache_prometheus_exporter container is ready in the pod. Apache prometheus exporter service is then started through pebble.

wordpress-replica_relation_changed

When any of the relation is changed, wordpress-k8s charm must run reconciliation between the current state and the desired state with new relation data to synchronize the replication instances. The reconciliation process is divided into 3 distinct steps: core, theme and plugin reconciliation. Core reconciliation setups up the necessary WordPress application configuration: secrets and database connection. Theme and Plugin respectively reconcile between currently installed themes and plugins with the incoming list of themes and plugins.

upgrade-charm

Upgrade charm event is fired on the upgrade charm command juju refresh wordpress-k8s. Sets up secrets in peer-relation databag for upgraded deployment of WordPress if not already set.