Automatic Flags

The reactive framework will automatically set some flags for your charm, based on lifecycle events from Juju. These flags can inform your charm of things such as upgrades, config changes, relation activity, etc.

With a few exceptions, noted below, these flags will be set by the framework but it is up to your charm to clear them, if need be. To avoid conflicts between layers, it is recommended that only the top-level charm layer (or interface layer, in the case of endpoint flags) use any of the automatic flags directly; any base layer should instead use register_trigger() to “wrap” the automatic flag with a layer-specific flag that can be safely used within that layer.

The flags that are set by the framework are:

upgrade.series.in-progress	This is set when the operator is about to start an OS upgrade, and removed after the operator has completed the upgrade. See OS Series Upgrades for more information.
config.changed	This is set when any config option has changed. [1]
config.changed.{option_name}	This is set for each config option that has changed. [1]
config.set.{option_name}	This is set for each config option whose value is not None, False, or an empty string. [1]
config.default.{option_name}	This is set for each config option whose value is equal to its default value, and cleared if it has been changed. [1]
leadership.is_leader	This is set when the unit is the leader. The unit will remain the leader for the remainder of the hook, but may not be leader in future hooks. [2]
leadership.changed	This is set when any leadership setting has changed. [2]
leadership.changed.{setting_name}	This is set for each leadership setting that has changed. [2]
leadership.set.{setting_name}	This is set for each leadership setting that has been to set to a value other than None. [2]
endpoint.{endpoint_name}.joined	This is set when a relation is joined on an endpoint. [3]
endpoint.{endpoint_name}.changed	This is set when relation data has changed. [3]
endpoint.{endpoint_name}.changed.{field}	This is set for each field of relation data which has changed. [3]
endpoint.{endpoint_name}.departed	This is set when a unit leaves a relation. [3]

[1]	(1, 2, 3, 4)

The config.* flags are currently managed by the base layer and are automatically cleared a the end of the hook context in which they were set. However, this is expected to change in the future, with the flags being set by this library instead and the automatic clearing behavior changed or removed.

[2]	(1, 2, 3, 4)

The leadership.* flags are currently managed by the leadership layer and the leadership.changed* flags are automatically cleared at the end of the hook context in which they were set. If this layer is not included by the charm or one of its base layers, these flags will not be set. However, this is expected to change in the future, with the flags being managed by this library instead and the automatic clearing behavior changed or removed.

[3]	(1, 2, 3, 4)

See Endpoint for more information on the endpoint.{endpoint_name}.* flags. The endpoint.{endpoint_name}.joined flag is automatically cleared when appropriate.