State (Scenario)

Scenario > State

In the context of Scenario, State refers to a monolithic data structure representing all data that is available to a charm at runtime. Simplifying somewhat, that information can be categorized depending on its source:

  • data coming from the juju controller and mediated by hook tools
  • data coming from the locally stored unit state (the unit state db)
  • data coming from environment variables
  • data coming from the workload and mediated by Pebble calls in the case of kubernetes charms

The State encapsulates all these types of data in a unified, immutable data structure.

More in detail, the information contained in State can be summarised as follows: in this table you can find

  • the name of the State component
  • its type in Python (and a link to the reference doc, where available)
  • the source of the data at runtime for that component, i.e. what part of the charm runtime this data is meant to mock
  • whether the data is writeable by the charm during hook execution
State component type source write
config Dict hook tool(s): config-get no
relations List[Relation] hook tool(s): relation-[get\|set\|list\|ids] no*
networks List[Network] hook tool(s): network-get no
unit_status StatusBase hook tool(s): status-[get\|set] yes
app_status StatusBase hook tool(s): status-[get\|set] yes
workload_version str hook tool(s): workload-version-set yes
leader bool hook tool(s): is-leader no
secrets List[Secret] hook tool(s): secret-[get\|set\|grant\|revoke\|add\|ids\|info-get\|remove] yes*
deferred List[DeferredEvent] local unit state db yes
stored_state List[StoredState] local unit state db yes
model Model envvars no
unit_id int envvars no
containers List[Container] (kubernetes only:) Pebble API yes

All data is readable according to the Juju access control rules: e.g. a follower unit cannot read its leader’s unit databag, nor write any databag other than its own.

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Last updated 11 months ago. Help improve this document in the forum.