Table of contents

1. How Metrics Work in Coldbrew
2. How to Add Custom Metrics
3. How to use Hystrix Metrics in Prometheus

How Metrics Work in Coldbrew

Coldbrew uses Prometheus to collect service metrics. By Default, Coldbrew will expose a /metrics endpoint that will return the metrics in the Prometheus exposition format on the configured HTTP port.

A collection of metrics are collected by default, including:

• Golang runtime metrics (e.g. memory usage, goroutine count, etc.)
• gRPC Client/Server metrics (e.g. request count, request duration, etc.)
• HTTP request metrics (e.g. request count, request duration, etc.)
• Hystrix-go circuit breaker metrics (e.g. request count, request duration, etc.) powered by Hystrix Prometheus

How to Add Custom Metrics

You can add custom metrics to your service by using the Prometheus Go client library and registering them with the default Prometheus registry. For example:

package main

import (
    "github.com/prometheus/client_golang/prometheus"
    "github.com/prometheus/client_golang/prometheus/promauto"
)

var (
    myCounter = promauto.NewCounter(prometheus.CounterOpts{
        Name: "my_counter",
        Help: "The total number of processed events",
    })
)

func myFunction() {
    ...
    myCounter.Inc()
    ...
}

These metrics will be automatically collected and exposed by Coldbrew on the /metrics endpoint.

To learn more about the Prometheus and the data types it supports, see here

How to use Hystrix Metrics in Prometheus

Hystrix Prometheus is a library that provides a Prometheus metrics collector for Hystrix-go. To use it, you can register the collector with the default Prometheus registry:

import (
    metricCollector "github.com/afex/hystrix-go/hystrix/metric_collector"
    "github.com/go-coldbrew/hystrixprometheus"
    "github.com/prometheus/client_golang/prometheus"
)

// setupHystrix sets up the hystrix metrics
// This is a workaround for hystrix-go not supporting the prometheus registry
func setupHystrix() {
	promC := hystrixprometheus.NewPrometheusCollector("hystrix", nil, prometheus.DefBuckets)
	metricCollector.Registry.Register(promC.Collector)
}

If you are using the go-coldbrew/core package, you can skip the above step as it will automatically register the collector for you. See Hystrix Prometheus for more details.