is_running() method for services

While developing Charms, we frequently have to check if the service is currently running, like so:

    def _is_running(self, container, service):
        """Helper method to determine if a given service is running in a given container"""
        try:
            service = container.get_service(service)
        except ModelError:
            return False
        return service.current == ServiceStatus.ACTIVE

        # Check we can get a list of services back from the Pebble API
        if self._is_running(container, "grafana"):
            logger.info("grafana already started")
            return

Could be useful if we have that method available as a part of the Operator Framework.

[niemeyer]

Having a is_running() method in the service sounds nice, but the implementation above is a bit suspect. It hides an API error and pretends the service is just not running. That doesn’t look like a great API behavior that we’d want to support in the operator framework itself.

This conversation and the code review also made me think that these APIs are not so nice to use. Maybe we should have a single get_services() method that returns something like a ServicesInfo, the plural of ServiceInfo. That type could indeed support more helpful methods, such as services.grafana.is_running() or/and services.is_running(“grafana”, “logger”). With that API the error checking might be done only once at the get_services() level, and the follow up usage would be free from exceptions because the data would be local.

@benhoyt What do you think?

[benhoyt]

Sounds good – will do today or tomorrow.