Prometheus/Micrometer

3 minute read

In Prometheus, metrics can be categorized into several types based on the * *nature of the data** they represent.

Counter

A counter is a cumulative metric that represents a single numerical value that only ever goes up (and resets when the process restarts). Counters are typically used to represent counts of events or increments over time.

private final MeterRegistry meterRegistry;
private Counter requestCounter;
private final LicenseService licenseService;

  @PostConstruct
  public void initializeMetrics() {
    // Counter
    requestCounter = Counter.builder("a_counter_http_requests_total")
            .description("Number of times the job request run")
            .tags("licenseJobCounter", "example")
            .register(meterRegistry);

      // Schedule task to simulate user arrivals
      Executors.newSingleThreadScheduledExecutor()
              .scheduleAtFixedRate(this::processRequest, 0, 100, TimeUnit.SECONDS);
  }

// Example method using Counter
public void processRequest() {
    licenseService.runJob();
    requestCounter.increment();
}

Gauge

A gauge is a metric that represents a single numerical value that can arbitrarily go up and down. Gauges are used for measured values like temperatures or current memory usage, where the value can both increase and decrease.

private final MeterRegistry meterRegistry;
AtomicInteger activeUsers = new AtomicInteger(0);
private Gauge activeUsersGauge;

@PostConstruct
public void initializeMetrics() {
activeUsersGauge =
    Gauge.builder("a_guage_active_users", activeUsers, AtomicInteger::get)
        .description("Number of active users")
        .register(meterRegistry);

// Schedule task to simulate user arrivals
ScheduledExecutorService executorService = Executors.newSingleThreadScheduledExecutor();
executorService.scheduleAtFixedRate(this::userLoggedIn, 0, 1, TimeUnit.SECONDS);
}

// Example method using Gauge
public int userLoggedIn() {
    return activeUsers.incrementAndGet();
}

Summary

Similar to a histogram, a summary samples observations (usually durations or sizes) over a sliding time window and calculates configurable quantiles over these samples.

private final MeterRegistry meterRegistry;
private DistributionSummary responseSizesSummary;

@PostConstruct
public void initializeMetrics() {
    // Distribution Summary (Summary)
    responseSizesSummary = DistributionSummary.builder("a_summary_http_response_sizes")
            .description("Distribution of HTTP response sizes")
            .baseUnit("bytes")
            .register(meterRegistry);

    processHttpResponse();
}

// Example method using Distribution Summary (Summary)
public void processHttpResponse() {
    int simulateHttpResponseSize = (int) (Math.random() * 1000);
    // Simulate processing and get response size
    responseSizesSummary.record(simulateHttpResponseSize);
}

Histogram

A histogram samples observations (usually durations or sizes) and counts them in configurable buckets. It also provides a sum of all observed values.

Untyped

Untyped metrics are similar to gauges, but they don’t have a specified type. They can be used when the value semantics don’t fit the typical gauge or counter models.

private final MeterRegistry meterRegistry;
private final AtomicLong customValue = new AtomicLong(0);
private final LicenseService licenseService;
@PostConstruct
public void initializeMetrics() {
    customValue.set(licenseService.runJob());
    // Untyped metric example
    meterRegistry.gauge("a_custom_untyped_metric", customValue); // Example of an untyped gauge
}

Timer

@PostConstruct
public void initializeMetrics() {

    // Timer
    requestTimer = Timer.builder("a_timer_http_request_duration_seconds")
            .description("HTTP request duration")
            .register(meterRegistry);

    // Long Task Timer
    longTaskTimer = LongTaskTimer.builder("a_long_task_http_request_duration_seconds")
            .description("Duration of long-running tasks")
            .register(meterRegistry);

    // Schedule task to simulate user arrivals
    ScheduledExecutorService executorService = Executors.newSingleThreadScheduledExecutor();
    executorService.scheduleAtFixedRate(this::processHttpRequest, 0, 100, TimeUnit.SECONDS);

}

Final output

http://localhost:8090/actuator/prometheus

# HELP a_counter_http_requests_total Number of times the job request run
# TYPE a_counter_http_requests_total counter
a_counter_http_requests_totallicenseJobCounterexample 1.0
# HELP a_custom_untyped_metric
# TYPE a_custom_untyped_metric gauge
a_custom_untyped_metric 1173.0
# HELP a_guage_active_users Number of active users
# TYPE a_guage_active_users gauge
a_guage_active_users 15.0
# HELP a_license_days_remaining Days remaining until License expiration
# TYPE a_license_days_remaining gauge
a_license_days_remaininglicense_days_remainingRemaining days 1173.0
# HELP a_license_expiration_counter_total
# TYPE a_license_expiration_counter_total counter
a_license_expiration_counter_totaltypecounter 18.0
# HELP a_license_expiration_days_summary_days Summary of days until License expiration
# TYPE a_license_expiration_days_summary_days summary
a_license_expiration_days_summary_days_count 0
a_license_expiration_days_summary_days_sum 0.0
# HELP a_license_expiration_days_summary_days_max Summary of days until License expiration
# TYPE a_license_expiration_days_summary_days_max gauge
a_license_expiration_days_summary_days_max 0.0
# HELP a_long_task_http_request_duration_seconds Duration of long-running tasks
# TYPE a_long_task_http_request_duration_seconds summary
a_long_task_http_request_duration_seconds_count 0
a_long_task_http_request_duration_seconds_sum 0.0
# HELP a_long_task_http_request_duration_seconds_max Duration of long-running tasks
# TYPE a_long_task_http_request_duration_seconds_max gauge
a_long_task_http_request_duration_seconds_max 0.0
# HELP a_summary_http_response_sizes_bytes Distribution of HTTP response sizes
# TYPE a_summary_http_response_sizes_bytes summary
a_summary_http_response_sizes_bytes_count 1
a_summary_http_response_sizes_bytes_sum 364.0
# HELP a_summary_http_response_sizes_bytes_max Distribution of HTTP response sizes
# TYPE a_summary_http_response_sizes_bytes_max gauge
a_summary_http_response_sizes_bytes_max 364.0
# HELP a_timer_http_request_duration_seconds HTTP request duration
# TYPE a_timer_http_request_duration_seconds summary
a_timer_http_request_duration_seconds_count 1
a_timer_http_request_duration_seconds_sum 0.296439955
# HELP a_timer_http_request_duration_seconds_max HTTP request duration
# TYPE a_timer_http_request_duration_seconds_max gauge
a_timer_http_request_duration_seconds_max 0.296439955

global: scrape_interval: 60s

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