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Configure Spring Boot to generate Prometheus metrics

Spring Boot is a popular Java framework for building modern applications. With the help of the actuator module and the micrometer library, you can configure a Spring Boot application to expose performance metrics in the Prometheus format.

To configure Spring Boot to generate Prometheus metrics, complete the following steps.

1. Set up the actuator module to enable the management endpoints and set up the micrometer module to provide the Prometheus endpoint that exposes Prometheus metrics.

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   dependencies {
       implementation 'org.springframework.boot:spring-boot-starter-actuator',
       Implementation ‘io.micrometer:micrometer-registry-prometheus’
   }

2. Enable the Prometheus endpoint in application.properties`` or application.yml`.

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   management.endpoint.prometheus.enabled=true
   management.endpoints.web.exposure.include=prometheus

   The first line enables the endpoint that provides metrics in the Prometheus format. The the second line tells Spring Boot to expose this endpoint as a Web API. You mighty have other endpoints listed here, such as info, health, and so on.

   For more information, refer to Exposing Endpoints.

3. To determine that your setup is correct, access the /actuator/prometheus endpoint of your web application, and verify that you see a list of metrics that look like the following example.

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   jvm_memory_used_bytes{area="heap",id="PS Survivor Space",} 2.012508E7
   …
   http_server_requests_seconds_count{exception="None",method="GET",outcome="SUCCESS",status="200",uri="/actuator/metrics",} 1.0
   http_server_requests_seconds_sum{exception="None",method="GET",outcome="SUCCESS",status="200",uri="/actuator/metrics",} 0.084955379
   …
   http_client_requests_seconds_count{clientName="chief.tsdb.dev.asserts.ai",method="POST",outcome="SUCCESS",status="200",uri="/select/0/prometheus/api/v1/query",} 4785.0
   http_client_requests_seconds_sum{clientName="chief.tsdb.dev.asserts.ai",method="POST",outcome="SUCCESS",status="200",uri="/select/0/prometheus/api/v1/query",} 238.762194814
   …

   The metrics shown usually include JVM, inbound HTTP requests, and outbound calls, among other metrics.

Optional setup to receive histogram metrics

By default, you only receive summary metrics. If you want the histogram metrics to calculate quantiles, enable them with following additional properties:

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management.metrics.distribution.percentiles-histogram.http.server.requests=true
management.metrics.distribution.percentiles-histogram.http.client.requests=true

The first property enables the histogram for inbound requests, and the second property enables the histogram for outbound HTTP calls.

Optional setup for custom instrumentation

Micrometer also provides annotations like @Timed and @Counted for you to monitor individual methods:

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package ai.asserts.tasks;

@Bean
public class TimerTask {
    @Timed(description = "Time spent processing all tenants", histogram = true)
    public void run() {
        processAllTenants();
    }
    ...
}

These annotations produce method_timed_seconds metrics as Prometheus summary metrics and optionally histogram metrics if you set histogram = true.

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method_timed_seconds_count{class="ai.asserts.tasks.TimerTask",exception="none",method="run",} 11.0
method_timed_seconds_sum{class="ai.asserts.tasks.TimerTask",exception="none",method="run",} 524.279248451
method_timed_seconds_bucket{class="ai.asserts.tasks.TimerTask",exception="none",method="run",le="0.001",} 0.0
…

Cardinality considerations

JVM metrics are usually small, so you need to focus on the HTTP request metrics when considering how many metrics get published.

For summary metrics, one URI, status code combination has three series on its latency: count, sum, and max, but histogram metrics are much more. One combination might have 50~100 buckets, so if you have 20 URLs, you will count 1000+ series per service instance. When the application reports status codes other than 200, such as 5xx or 4xx, then additional metrics are reported.

For inbound calls, the number of URIs usually matches the number of API endpoints your service provides. But for outbound calls, depending on how you customize your RestTemplate, URIs could contain query strings, which can cause a cardinality explosion. If you enable histogram for outbound calls, check the URIs and if necessary, fix the RestTemplate.

RED metric KPIs

Asserts automatically tracks the following list of key performance indicators for Request, Error, and Duration (RED) metrics.

RED metrics alerts

Asserts automatically tracks the short-term and long-term request and latency trends for Anomaly detection by URI and method names. Similarly, thresholds can be set for latency averages and P99 to record breaches. Error ratios are tracked against availability goals (default, 99.9%) and breaches (default, 10%).

JVM GC alerts

Asserts tracks the JVM GC Count and Time from micrometer metrics. You can tune these thresholds.

Service KPI dashboard

Asserts aggregates data from Micrometer, cAdvisor, kubelet, and node-exporter to present a dashboard with the following KPIs:

• Request Rate
  • Type: inbound, outbound, method, executor, logger, custom
  • Context: URI, method name et al.
• Latency Average
• Latency P99
• Error Ratio and Error Rate
• CPU %
• CPU Cores Used
• CPU Throttle
• Memory %
• Memory Bytes
• Disk Usage
• Network Usage

JVM Micrometer KPI dashboard

The JVM Micrometer KPI dashboard includes the following KPIs:

• JVM memory
• CPU-Usage, Load, Threads, Thread States, File Descriptors, Log Events
• JVM Memory Pools (Heap, Non-Heap)
• Garbage Collection
• Classloading
• Direct-/Mapped-Buffer