4.x Provide initial temp config for MP metrics DistributionCustomizations

[tjquinno]

Environment Details

• Helidon Version: 4.1.4
• Helidon SE or Helidon MP MP
• JDK version:
• OS:
• Docker version (if applicable):

---

Problem Description

MP Metrics 5.1 added the ability for users configure percentile and bucket settings in microprofile-config.properties.

Helidon MP initializes these settings as part of the metrics CDI extension late-stage start-up work. As usual, in the absence of config settings for these values Helidon applies defaults.

A user reports that a test that uses MP metrics but which does not use @HelidonTest and therefore does not initialize the Helidon MP container began to fail starting with Helidon 4.1.4. That's because, without the metrics CDI extension running, no code initializes the new config settings. As a result, attempts by metrics to dereference the settings threw an NPE.

An easy workaround is to annotated such tests with @HelidonTest. It would also be simple enough for Helidon to provide initial default settings, subject to change during actual startup, to avoid such NPEs.

Steps to reproduce

Create a test without @HelidonTest, run separately from tests with that annotation:

class TestDistributionCustomizationsNoInit {

    private static MetricRegistry metricRegistry;

    @BeforeAll
    static void initRegistry() {
        metricRegistry = RegistryFactory.getInstance().getRegistry(MetricRegistry.APPLICATION_SCOPE);
    }

    @Test
    void checkDistributionCustomizations() {
        // The following triggers an NPE because this test does not use @HelidonTest
        // and therefore the normal metrics CDI extension initialization code --which sets up the distribution
        // customizations -- does not run.
        Timer timer = metricRegistry.timer("testTimer");
        assertThat("Timer", timer, notNullValue());
    }
} 

[tjquinno]

This problem has now also been reported in an app (not a test). The app contains a CDI extension which registers metrics before the @Observes @Initialized(ApplicationScope.class) init) event which is before Helidon's CDI metrics extension has properly set up metrics. Extensions should registers metrics only after app-scoped beans have been initialized to make sure Helidon MP has had a chance to properly set up metrics.

That said, the changes in the PR should address this problem as well.