Fallbacks

Components Fallbacks contain the set of Actions to be executed when a failure status is detected. Fallbacks are defines with an Action or a list of Actions to be executed in sequence. Each Action in the list is retried until max_retries is reached.

Fallbacks and Health Status

Fallbacks Categories:

Each component has 3 built-in possible fallbacks categories along with the possibility to set a behavior for “any failure” and a “giveup” behavior that is executed when all failure actions are exhausted.

• on_component_fail

• on_algorithm_fail

• on_system_fail

• on_any_fail

• on_giveup

The first three are designed to correspond to the three different Health Status a Component can take other than “Healthy” status. ‘on_any_fail’ is used to define a fallback policy regardless of the failure category. Finally, ‘on_give’ is the final Action the Component will execute when all the fallbacks and retries are exhausted.

Default behavior in a Component:

The default behavior in a Component is for the component to broadcast the status on any detected failure. By default the component sets ‘on_any_fail’ Fallback to ‘Action(self.broadcast_status)’ with ‘max_retries=None’.

Action(s) set for ‘on_any_fail’ is executed for any failure for which no fallback action is defined.

Note

Each Component already owns its own ComponentFallback configured to the previous default behavior. The only thing required is to configure the Actions executed at each (or any) failure type.

Usage in a Component:

    from ros_sugar.core import BaseComponent
    from ros_sugar.actions import ComponentActions

    my_component = BaseComponent(component_name='test_component')

    # Set fallback for component failure to restart the component
    my_component.on_component_fail(fallback=ComponentActions.restart(component=my_component))

    # Change fallback for any failure
    my_component.on_fail(fallback=Action(my_component.restart))

    # First broadcast status, if another failure happens -> restart
    my_component.on_fail(fallback=[Action(my_component.broadcast_status), Action(my_component.restart)])