[jboss-jira] [JBoss JIRA] (WFCORE-4190) Distinguish undefined metric value

[Jeff Mesnil (Jira)]

    [ https://issues.jboss.org/browse/WFCORE-4190?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13654481#comment-13654481 ] 

Jeff Mesnil commented on WFCORE-4190:
-------------------------------------

When the microprofile-metrics-smallrye extension will register MP metrics from WildFly metrics, it will ignore (and not expose from its HTTP endpoints) any metric that returns an undefined value.

> Distinguish undefined metric value
> ----------------------------------
>
>                 Key: WFCORE-4190
>                 URL: https://issues.jboss.org/browse/WFCORE-4190
>             Project: WildFly Core
>          Issue Type: Bug
>          Components: Management
>    Affects Versions: 7.0.0.Alpha4
>            Reporter: Jeff Mesnil
>            Assignee: Jeff Mesnil
>            Priority: Critical
>
> WildFly resources can registered metrics for runtime read-only attributes whose value change during server activity.
> Some of these metrics are "disabled" by default (as they may be expensive to compute) and are enabled using a boolean attribute named statistics-enabled in their resource tree.
> When these metrics would not be able to compute their value, they could register a "undefined metric value" that would be returned by the :read-attribute handler if the metric read handler would return an undefined value.
> This causes a significant issue when one observes WildFly as it generates metrics figures that gives an incorrect observation of the server activity.
> Typical example is undertow metrics to see bytes sent and received on its http(s)-listeners[1].
> When the metric is defined[2], it specifies an undefined metric value of 0.
> From the outside, when a monitoring tool will fetch value for the bytes-sent metric, it may return 0 in 2 different cases:
> * the metric is not enabled if the statistics-enabled attribute at [3] is false (which is the case by default). This does not mean that there is no network traffic.
> * statistics-enabled is true but there is no network traffic on the HTTP listener
> These 2 cases are wildly different but it is not possible to distinguish between them
> In order to distinguish these 2 cases, the :read-attribute operation (and by extension the :read-resource operation) will be enhanced with a "include-undefined-metric" operation parameter.
> This parameter is taken into account only for metric attribute:
> * if include-undefined-metric is true, the operation will return a undefined value from the metric's read handler *without substituting it by the *undefined metric value* from the metric AttributeDefinition
> * if the flag is false (by default), the current behaviour is used (if the read handler returns an undefined value, uses the  *undefined metric value* from the metric AttributeDefinition.
> This will allow external monitoring tool (as well as the metrics subsystem from WFLY-10712) to know that the metric does not return a meaningful value.
> When I looked at various metrics registered in WildFly, some of them returns a meaningless value if the runtime code can not compute the value (e.g. Undertow statistics returns 0 if they are not able to obtain the underlying statistics[4]) in addition to defined an "undefined metric value" from the metric AttributeDefinition.
> These read handlers would have to be fixed so they MUST NOT return a defined value that does not correspond to the actual value required by the operation.
> [1] http://wildscribe.github.io/WildFly/14.0/subsystem/undertow/server/http-listener/index.html
> [2] https://github.com/wildfly/wildfly/blob/8f620bbe6d481c9c2c6422e2250326a98c378056/undertow/src/main/java/org/wildfly/extension/undertow/ListenerResourceDefinition.java#L170-L172
> [3] http://wildscribe.github.io/WildFly/14.0//subsystem/undertow/index.html#attr-statistics-enabled
> [4] https://github.com/wildfly/wildfly/blob/8f620bbe6d481c9c2c6422e2250326a98c378056/undertow/src/main/java/org/wildfly/extension/undertow/ListenerResourceDefinition.java#L268



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