support prometheus export with micrometer

kotlin/.gitignore

@@ -17,3 +17,4 @@ build
 out/
 .scannerwork/
 cookie.txt
+prom.txt

kotlin/README.adoc

@@ -131,3 +131,33 @@ $ curl -sS http://localhost:8080/actuator/health
 == Gradle Version Catalog
 
 * https://blog.jdriven.com/2022/11/gradle-goodness-defining-plugin-versions-using-version-catalog/
+
+== Metrics / Monitoring
+
+* https://github.com/kirshiyin89/springboot-monitoring-demo/tree/feature/monitoring-with-custom-endpoints-and-security[How To Secure Custom Spring Boot Actuator Endpoints and Add Prometheus Metrics]
+* https://docs.spring.io/spring-boot/docs/2.0.x/reference/html/production-ready-metrics.html[Part V. Spring Boot Actuator: Production-ready features - Metrics / Micrometer]
+* https://stackoverflow.com/questions/48451381/spring-boot-actuator-micrometer-metrics-disable-some[Spring Boot Actuator/Micrometer Metrics Disable Some]
+* https://medium.com/javarevisited/unlocking-precision-metrics-in-spring-boot-with-micrometer-a-comprehensive-guide-6d72d6eaaf00[Unlocking Precision Metrics in Spring Boot with Micrometer: A Comprehensive Guide]
+* https://docs.spring.io/spring-boot/docs/current/reference/html/actuator.html#actuator.endpoints.security[Spring Boot Actuator Endpoint Security]
+* https://www.callicoder.com/spring-boot-actuator-metrics-monitoring-dashboard-prometheus-grafana/[Spring Boot Actuator metrics monitoring with Prometheus and Grafana]
+
+.Example for filtered /actuator/metrics endpoint
+----
+# HELP jvm_memory_max_bytes The maximum amount of memory in bytes that can be used for memory management
+# TYPE jvm_memory_max_bytes gauge
+jvm_memory_max_bytes{app="angkor-api",area="nonheap",id="CodeCache",} 5.0331648E7
+jvm_memory_max_bytes{app="angkor-api",area="nonheap",id="Metaspace",} -1.0
+jvm_memory_max_bytes{app="angkor-api",area="nonheap",id="Compressed Class Space",} 1.073741824E9
+jvm_memory_max_bytes{app="angkor-api",area="heap",id="G1 Eden Space",} -1.0
+jvm_memory_max_bytes{app="angkor-api",area="heap",id="G1 Survivor Space",} -1.0
+jvm_memory_max_bytes{app="angkor-api",area="heap",id="G1 Old Gen",} 8.589934592E9
+# HELP process_cpu_usage The "recent cpu usage" for the Java Virtual Machine process
+# TYPE process_cpu_usage gauge
+process_cpu_usage{app="angkor-api",} 0.0
+# HELP jdbc_connections_active Current number of active connections that have been allocated from the data source.
+# TYPE jdbc_connections_active gauge
+jdbc_connections_active{app="angkor-api",name="dataSource",} 0.0
+# HELP process_start_time_seconds Start time of the process since unix epoch.
+# TYPE process_start_time_seconds gauge
+process_start_time_seconds{app="angkor-api",} 1.707417503734E9
+----

kotlin/build.gradle.kts

@@ -96,11 +96,14 @@ dependencies {
     implementation(libs.bundles.rome)
     implementation(libs.bucket4j)
 
-
     // Persistence (Postgres, JPA, Hibernate)
     implementation(libs.postgresql)
     implementation(libs.bundles.flyway)
     implementation(libs.hypersistence.utils.hibernate)
+
+    // Monitoring / Micrometer
+    implementation(libs.micrometer.prometheus)
+
 
     // Jackson JSON Parsing Dependencies
     // For Gradle users, if you use the Spring Boot Gradle plugin you can omit the version number to adopt

kotlin/gradle/libs.versions.toml

@@ -90,6 +90,8 @@ wiremock = { module = "com.github.tomakehurst:wiremock-standalone", version = "3
 kotlin-gradle-plugin = { module = "org.jetbrains.kotlin:kotlin-gradle-plugin", version.ref = "kotlin" }
 kotlin-all-open = { module = "org.jetbrains.kotlin:kotlin-allopen", version.ref = "kotlin" }
 
+micrometer-prometheus = { module = "io.micrometer:micrometer-registry-prometheus", version = "1.12.2" }
+
 
 [bundles]
 # Nice ... we can bundle libs and use like "libs.bundles.flyway"

kotlin/src/main/kotlin/net/timafe/angkor/config/MetricsConfig.kt

@@ -0,0 +1,68 @@
+package net.timafe.angkor.config
+
+import io.micrometer.core.instrument.Meter
+import io.micrometer.core.instrument.MeterRegistry
+import io.micrometer.core.instrument.config.MeterFilter
+import io.micrometer.core.instrument.config.MeterFilterReply
+import org.springframework.boot.actuate.autoconfigure.metrics.MeterRegistryCustomizer
+import org.springframework.context.annotation.Bean
+import org.springframework.context.annotation.Configuration
+
+
+@Configuration
+class MetricsConfig {
+
+    companion object {
+        val FilterNames = setOf(
+            "hikaricp.connections.max",
+            "hikaricp.connections.active",
+            "hikaricp.connections.acquire",
+            "hikaricp.connections",
+            "jvm.memory.max",
+            "jvm.memory.committed",
+            "jvm.memory.used",
+            "process.start.time",
+            "process.uptime",
+            "system.cpu.usage",
+            "tomcat.sessions.active.current",
+            "tomcat.sessions.active.max",
+            "tomcat.sessions.created"
+        )
+    }
+
+    // add common tags
+    @Bean
+    fun metricsCommonTags(): MeterRegistryCustomizer<MeterRegistry> {
+        return MeterRegistryCustomizer<MeterRegistry> { registry: MeterRegistry ->
+            registry.config().commonTags("app", "angkor-api")
+        }
+    }
+
+    /**
+     * Reduce metrics https://stackoverflow.com/a/54097060/4292075
+     * https://github.com/micrometer-metrics/micrometer-docs/blob/main/src/docs/concepts/meter-filters.adoc#deny-or-accept-meters
+     * Example Names (it uses dots, not the prometheus style underscore notation)
+     *   http.server.requests.active
+     *   spring.security.filter.active     *
+     */
+
+    @Bean
+    fun meterFilter(): MeterFilter {
+        return object : MeterFilter {
+            override fun accept(id: Meter.Id): MeterFilterReply {
+                //listOf("jdbc.connections.active", "jvm.memory.max","process.cpu.usage","process.start").forEach {
+                FilterNames.forEach {
+                    if (id.name.startsWith(it)) {
+                        return MeterFilterReply.NEUTRAL
+                    }
+                }
+                // println(id.name)
+//                if (id.getName().startsWith("jvm.")) {
+//                    return MeterFilterReply.DENY
+//                }
+                return MeterFilterReply.DENY // deny all other
+            }
+        }
+    }
+
+}

kotlin/src/main/kotlin/net/timafe/angkor/config/WebConfig.kt

@@ -6,6 +6,7 @@ import org.slf4j.LoggerFactory
 import org.springframework.context.annotation.Configuration
 import org.springframework.context.annotation.Profile
 import org.springframework.http.converter.HttpMessageConverter
+import org.springframework.http.converter.StringHttpMessageConverter
 import org.springframework.http.converter.json.MappingJackson2HttpMessageConverter
 import org.springframework.web.servlet.config.annotation.CorsRegistry
 import org.springframework.web.servlet.config.annotation.EnableWebMvc
@@ -38,9 +39,14 @@ class WebConfig(private val objectMapper: ObjectMapper)  : WebMvcConfigurer{
      #
      * https://stackoverflow.com/a/55958912/4292075
      * https://stackoverflow.com/a/49405364/4292075
+     *
+     * Similar issue with actuator/prometheus endpoint if there's no
+     * HttpMessageConverter registered that could handle the "text/plain" MediaType, only
+     * https://stackoverflow.com/a/52085616/4292075
      */
     override fun configureMessageConverters(converters: MutableList<HttpMessageConverter<*>?>) {
         converters.add(MappingJackson2HttpMessageConverter(objectMapper))
+        converters.add( StringHttpMessageConverter())
         // addDefaultHttpMessageConverters(converters)
         super.configureMessageConverters(converters)
     }

kotlin/src/main/kotlin/net/timafe/angkor/web/MetricsController.kt

@@ -4,6 +4,7 @@ import com.fasterxml.jackson.databind.JsonNode
 import jakarta.servlet.http.HttpServletRequest
 import net.timafe.angkor.config.AppProperties
 import net.timafe.angkor.config.Constants
+import net.timafe.angkor.config.MetricsConfig.Companion.FilterNames
 import net.timafe.angkor.domain.dto.MetricDetails
 import net.timafe.angkor.service.MetricsService
 import net.timafe.angkor.web.vm.BooleanResult
@@ -31,23 +32,6 @@ class MetricsController(
 
     private val log: Logger = LoggerFactory.getLogger(this.javaClass)
 
-    companion object {
-        val filterNames = setOf(
-            "hikaricp.connections.max",
-            "hikaricp.connections.active",
-            "hikaricp.connections.acquire",
-            "hikaricp.connections",
-            "jvm.memory.max",
-            "jvm.memory.committed",
-            "jvm.memory.used",
-            "process.start.time",
-            "process.uptime",
-            "system.cpu.usage",
-            "tomcat.sessions.active.current",
-            "tomcat.sessions.active.max",
-            "tomcat.sessions.created"
-        )
-    }
 
     @GetMapping("${Constants.API_LATEST}/stats")
     fun entityStats(): Map<String, Long> {
@@ -64,7 +48,7 @@ class MetricsController(
         metrics.add(MetricDetails("kotlin.version", "Kotlin Version", KotlinVersion.CURRENT.toString(), null))
         metrics.add(MetricDetails("app.version", "App Version (API)", appProperties.version, null))
         metrics.addAll(metricsEndpoint.listNames().names
-            .filter { filterNames.contains(it) }
+            .filter { FilterNames.contains(it) }
             .map {
                 val resp: MetricsEndpoint.MetricDescriptor = metricsEndpoint.metric(it, null)
                 MetricDetails(resp.name, resp.description, resp.measurements[0].value, resp.baseUnit)

kotlin/src/main/resources/application.yml

@@ -57,11 +57,15 @@ management:
   endpoints:
     web:
       exposure:
-        include: info,health,metrics
+        include: info,health,metrics,prometheus
   endpoint:
     # https://www.callicoder.com/spring-boot-actuator/#displaying-detailed-health-information
     health:
       show-details: always
+  prometheus:
+    metrics:
+      export:
+        enabled: true # new key, metrics.prometheus ... is deprecated
 
 server:
   error:

kotlin/src/test/kotlin/net/timafe/angkor/web/MetricsControllerTest.kt

@@ -19,6 +19,8 @@ class MetricsControllerTest(private val controller: MetricsController) {
 
     fun `test admin status`() {
         val stats = controller.metrics()
+        // Size should all custom metrics registered in MetricsController
+        // plus those that are not ignored in net.timafe.angkor.config.MetricsConfig
         Assertions.assertThat(stats.size).isGreaterThan(15)
     }