0x01 Counter

计数器是一种累积指标，表示单个单调递增计数器，其值只能在重新启动时增加或重置为零。例如，您可以使用计数器来表示所服务的请求数、已完成的任务数或错误数。

import io.prometheus.client.Counter;
class YourClass {
  static final Counter requests = Counter.build()
     .name("requests_total").help("Total requests.").register();

  void processRequest() {
    requests.inc();
    // Your code here.
  }
}

0x02 Gauge

Gauge是一种度量，表示可以任意上升和下降的单个数值。通常用于当前内存使用情况、cpu使用情况等测量值。

class YourClass {
  static final Gauge inprogressRequests = Gauge.build()
     .name("inprogress_requests").help("Inprogress requests.").register();

  void processRequest() {
    inprogressRequests.inc();
    // Your code here.
    inprogressRequests.dec();
  }
}

0x03 Histogram

直方图对观察结果（通常是请求持续时间或响应大小）进行采样，并将它们计数到可配置的存储桶中。它还提供所有观察值的总和。

class YourClass {
  static final Histogram requestLatency = Histogram.build()
     .name("requests_latency_seconds").help("Request latency in seconds.").register();

  void processRequest(Request req) {
    Histogram.Timer requestTimer = requestLatency.startTimer();
    try {
      // Your code here.
    } finally {
      requestTimer.observeDuration();
    }
  }
}

class YourClass {
  static final Histogram requestLatency = Histogram.build()
     .name("requests_latency_seconds").help("Request latency in seconds.").register();

  void processRequest(Request req) {
    requestLatency.time(new Runnable() {
      public abstract void run() {
        // Your code here.
      }
    });


    // Or the Java 8 lambda equivalent
    requestLatency.time(() -> {
      // Your code here.
    });
  }
}

0x04 Summary

与直方图类似，摘要对观察结果进行采样（通常是请求持续时间和响应大小等）。虽然它还提供观察总数和所有观察值的总和，但它计算滑动时间窗口上的可配置分位数。

class YourClass {

  private static final Summary requestLatency = Summary.build()
      .name("requests_latency_seconds")
      .help("request latency in seconds")
      .register();

  private static final Summary receivedBytes = Summary.build()
      .name("requests_size_bytes")
      .help("request size in bytes")
      .register();

  public void processRequest(Request req) {
    Summary.Timer requestTimer = requestLatency.startTimer();
    try {
      // Your code here.
    } finally {
      requestTimer.observeDuration();
      receivedBytes.observe(req.size());
    }
  }
}

0x05 Label

所有metrics都可以有label，用来对相关的time series进行分组。

class YourClass {
  static final Counter requests = Counter.build()
     .name("my_library_requests_total").help("Total requests.")
     .labelNames("method").register();

  void processGetRequest() {
    requests.labels("get").inc();
    // Your code here.
  }
}

0x06 实战

@RestController
public class OriginalWebController {
    private final Counter counter;
    private final Histogram histogram;

    @Autowired
    private WebService service;
    public OriginalWebController(CollectorRegistry collectorRegistry) {
        counter = Counter.build()
                .name("test_prometheus_sdk_metrics1")
                .help("prometheus sdk counter...")
                .labelNames("language")
                .register(collectorRegistry);

        histogram = Histogram.build()
                .name("test_prometheus_sdk_metrics2")
                .help("prometheus sdk histogram...")
                .labelNames("language")
                .register(collectorRegistry);
    }

    @GetMapping("/monitor")
    public String monitor(@RequestParam String language) {
        // 统计次数
        counter.labels(language).inc();

        // 统计耗时
        Histogram.Timer timer = histogram.labels(language).startTimer();
        // do something...
        String result = service.doMonitor(language);
        timer.observeDuration();
        return result;
    }
}

0x07 具体的监控数据

这里以counter和histogram为例看一下具体的指标数据：

counter metrics

histogram metrics