[sling-whiteboard] 03/05: metrics-prometheus: add basic documentation

[ro...@apache.org]

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rombert pushed a commit to branch master
in repository https://gitbox.apache.org/repos/asf/sling-whiteboard.git

commit ea1e6fee78215fe661af0486187b7e2b6472503b
Author: Robert Munteanu <ro...@apache.org>
AuthorDate: Wed Aug 30 00:22:29 2023 +0200

    metrics-prometheus: add basic documentation
---
 metrics-prometheus/README.md                                   | 10 ++++++++++
 .../metrics/prometheus/impl/DefaultJvmMetricsRegistrar.java    |  3 +++
 .../sling/metrics/prometheus/impl/WrapperMetricsServlet.java   |  7 +++++++
 3 files changed, 20 insertions(+)

diff --git a/metrics-prometheus/README.md b/metrics-prometheus/README.md
new file mode 100644
index 00000000..5e4e4176
--- /dev/null
+++ b/metrics-prometheus/README.md
@@ -0,0 +1,10 @@
+[![Apache Sling](https://sling.apache.org/res/logos/sling.png)](https://sling.apache.org)
+
+# Apache Sling Commons Metrics Prometheus
+
+This module is part of the [Apache Sling](https://sling.apache.org) project.
+
+This bundle exposes the collected metrics under the `/metrics` path and provides the following features:
+
+- exports JVM metrics by default
+- supports multiple `MetricRegistry` instances
\ No newline at end of file
diff --git a/metrics-prometheus/src/main/java/org/apache/sling/metrics/prometheus/impl/DefaultJvmMetricsRegistrar.java b/metrics-prometheus/src/main/java/org/apache/sling/metrics/prometheus/impl/DefaultJvmMetricsRegistrar.java
index b84f16d7..9ac10c17 100644
--- a/metrics-prometheus/src/main/java/org/apache/sling/metrics/prometheus/impl/DefaultJvmMetricsRegistrar.java
+++ b/metrics-prometheus/src/main/java/org/apache/sling/metrics/prometheus/impl/DefaultJvmMetricsRegistrar.java
@@ -21,6 +21,9 @@ import org.osgi.service.component.annotations.Component;
 
 import io.prometheus.client.hotspot.DefaultExports;
 
+/**
+ * Registers the default JVM metrics with the default registry
+ */
 @Component(immediate = true)
 public class DefaultJvmMetricsRegistrar {
 
diff --git a/metrics-prometheus/src/main/java/org/apache/sling/metrics/prometheus/impl/WrapperMetricsServlet.java b/metrics-prometheus/src/main/java/org/apache/sling/metrics/prometheus/impl/WrapperMetricsServlet.java
index 9fe7ce62..a9902e88 100644
--- a/metrics-prometheus/src/main/java/org/apache/sling/metrics/prometheus/impl/WrapperMetricsServlet.java
+++ b/metrics-prometheus/src/main/java/org/apache/sling/metrics/prometheus/impl/WrapperMetricsServlet.java
@@ -48,6 +48,13 @@ import io.prometheus.client.CollectorRegistry;
 import io.prometheus.client.dropwizard.DropwizardExports;
 import io.prometheus.client.exporter.MetricsServlet;
 
+/**
+ * Exports metrics taking into account multiple registry instances
+ * 
+ * <p>For historical reasons, Sling and Oak have their own metrics registry implementations. This
+ * may occur for other applications as well so we take care to gracefully handle multiple child
+ * registries.</p>
+ */
 @HttpWhiteboardServletPattern("/metrics")
 @HttpWhiteboardContextSelect("(osgi.http.whiteboard.context.name=org.osgi.service.http)")
 @Component(service = Servlet.class)