[jira] [Created] (BROOKLYN-176) Expensive polling of driver.isRunning is too frequent

["Aled Sage (JIRA)" <ji...@apache.org>]

Aled Sage created BROOKLYN-176:
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             Summary: Expensive polling of driver.isRunning is too frequent
                 Key: BROOKLYN-176
                 URL: https://issues.apache.org/jira/browse/BROOKLYN-176
             Project: Brooklyn
          Issue Type: Improvement
    Affects Versions: 0.9.0-SNAPSHOT
            Reporter: Aled Sage


Many of our entities by default poll driver.isRunning, calling it every 5 seconds. This often involves a ssh execution, which is cpu intensive. This doesn't scale.

This polling should only be done if there is no other/better way to determine if an entity is unhealthy. We should use other mechanisms (e.g. checking if a web-server is reachable over http), and only resort to calling driver.isRunning to provide additional information if that other check fails.

However, turning it off is a little tricky in the current code. The SoftwareProcess.initEnrichers does:

{noformat}
ServiceNotUpLogic.updateNotUpIndicator(this, SERVICE_PROCESS_IS_RUNNING, "No information yet on whether this service is running");
{noformat}

The SERVICE_PROCESS_IS_RUNNING value is cleared by `connectServiceUpIsRunning`, which polls the driver.isRunning`. If you don't call `connectServiceUpIsRunning` then you'd need to do something yourself to ensure `SERVICE_PROCESS_IS_RUNNING` is cleared.

We also need to better define the best practices for checking serviceUp in a pure-YAML entity. We need better examples (and a simpler way) to hook up sensor feeds, such as http feeds etc, for polling an entity's health.

There are a few areas of related code:

* The attribute `service.notUp.indicators` allows multiple ways of determining if an entity is healthy. If any of these indicators have put an entry into ``service.notUp.indicators` map, then the entity is marked as serviceUp=false.

* The attribute `service.notUp.diagnostics` is populated with additional info when an entity fails. See `SoftwareProcessImpl.ServiceNotUpDiagnosticsCollector`, which is executed when serviceUp is set to false or when serviceState changes. The defaults are to check if the machine is ssh'able, and check driver.isRunning.

* The `HttpRequestSensor` is usable in YAML, via an `EntityInitializer`, to add an HTTP-based sensor feed.

* Config key `SoftwareProcess.RETRIEVE_USAGE_METRICS`, disables (some) polling for usage/performance metrics, but will still do health metrics such as service-up.




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