Prometheus type Collector - how to feed maps with my own data

Question

Disclaimer: I am new to Golang and haven't done much programming in any other language before. I still hope someone can point me in the right direction though.

The goal is: As per the 'Example' section under Prometheus Golang module (https://godoc.org/github.com/prometheus/client_golang/prometheus#Collector) and the part where it's mentioned "// Just example fake data." to use my own real data of course.

My data comes in JSON format from a RabbitMQ endpoint. I parse JSON and I can create my own maps with the right key:value that I need as part of a goroutine under the func main() scope.

Suppose my map looks as follows: [ "device1" : 754, "device2" : 765, ]

For the code, let's follow the original example.

package main

import (
    "log"
    "net/http"
    "fmt"

    "github.com/prometheus/client_golang/prometheus"
    "github.com/prometheus/client_golang/prometheus/promhttp"
)

type ClusterManager struct {
    Zone string
    // Contains many more fields not listed in this example.
}

func (c *ClusterManager) ReallyExpensiveAssessmentOfTheSystemState() (
    oomCountByHost map[string]int, ramUsageByHost map[string]float64,
) {
        // Just example fake data.
        oomCountByHost = map[string]int{
            "foo.example.org": 42,
            "bar.example.org": 2001,
        }
        ramUsageByHost = map[string]float64{
            "foo.example.org": 6.023e23,
            "bar.example.org": 3.14,
        }
        return
}

type ClusterManagerCollector struct {
    ClusterManager *ClusterManager
}

var (
    oomCountDesc = prometheus.NewDesc(
        "clustermanager_oom_crashes_total",
        "Number of OOM crashes.",
        []string{"host"}, nil,
    )
    ramUsageDesc = prometheus.NewDesc(
        "clustermanager_ram_usage_bytes",
        "RAM usage as reported to the cluster manager.",
        []string{"host"}, nil,
    )
)

func (cc ClusterManagerCollector) Describe(ch chan<- *prometheus.Desc) {
    prometheus.DescribeByCollect(cc, ch)
}

func (cc ClusterManagerCollector) Collect(ch chan<- prometheus.Metric) {
    oomCountByHost, ramUsageByHost := cc.ClusterManager.ReallyExpensiveAssessmentOfTheSystemState()
    for host, oomCount := range oomCountByHost {
        ch <- prometheus.MustNewConstMetric(
            oomCountDesc,
            prometheus.CounterValue,
            float64(oomCount),
            host,
        )
    }
    for host, ramUsage := range ramUsageByHost {
        ch <- prometheus.MustNewConstMetric(
            ramUsageDesc,
            prometheus.GaugeValue,
            ramUsage,
            host,
        )
    }
}

func NewClusterManager(zone string, reg prometheus.Registerer) *ClusterManager {
    c := &ClusterManager{
        Zone: zone,
    }
    cc := ClusterManagerCollector{ClusterManager: c}
    prometheus.WrapRegistererWith(prometheus.Labels{"zone": zone}, reg).MustRegister(cc)
    return c
}

func main() {
    conn, err := amqp.Dial("amqp://guest:guest@localhost:5672/")
    failOnError(err, "Failed to connect to RabbitMQ")
    defer conn.Close()

    ch, err := conn.Channel()
    failOnError(err, "Failed to open a channel")
    defer ch.Close()

    q, err := ch.QueueDeclare("hello", false, false, false, false, nil)
    failOnError(err, "Failed to declare a queue")

    msgs, err := ch.Consume(q.Name, "", true, false, false, false, nil)
    failOnError(err, "Failed to register a consumer")

    forever := make(chan bool)

    go func() {
        for d := range msgs {
            var streams []byte
            streams = d.Body

            var metrics sStreamingMetrics
            err := json.Unmarshal(streams, &metrics)
            if err != nil {
                fmt.Println(err)
            }

            var category string
            category = metrics.Resource.Category

            if category == "server" {
               myMap := make(map[string]float64)
               MyMap [metrics.Resource.ResourceDataList[0].ResourceId] = metrics.Resource.ResourceDataList[0].MetricSampleList[0].ValueArray[0]
             }
    }()

    reg := prometheus.NewPedanticRegistry()

    NewClusterManager("zone", reg)

    reg.MustRegister(
        prometheus.NewProcessCollector(prometheus.ProcessCollectorOpts{}),
        prometheus.NewGoCollector(),
    )

    http.Handle("/metrics", promhttp.HandlerFor(reg, promhttp.HandlerOpts{}))
    log.Fatal(http.ListenAndServe(":8080", nil))
    log.Printf(" [*] Waiting for logs. To exit press CTRL+C")
    <-forever
}

//relevant structs go here for parsing JSON

Added the goroutine and the main for a bigger picture. There's concurency as I'll be receiving data from time to time. I think the skill I am missing here is how to call the function so that key:values from myMap go into func (c *ClusterManager) ReallyExpensiveAssessmentOfTheSystemState() ( oomCountByHost map[string]int, ramUsageByHost map[string]float64,){}

Answer 1

I think the skill I am missing here is how to call the function so that key:values from myMap go into func (c *ClusterManager) ReallyExpensiveAssessmentOfTheSystemState() ( oomCountByHost map[string]int, ramUsageByHost map[string]float64,){}

ReallyExpensiveAssessmentOfTheSystemState is called in the Collect method. Your map doesn't "go into" that method, it is returned by ReallyExpensiveAssessmentOfTheSystemState.

Simply move the code from the goroutine into ReallyExpensiveAssessmentOfTheSystemState:

func (c *ClusterManager) ReallyExpensiveAssessmentOfTheSystemState() map[string]float64 {
    myMap := make(map[string]float64)
    myMap["device1"] = 754
    myMap["device2"] = 765

    return myMap
}

func (cc ClusterManagerCollector) Collect(ch chan<- prometheus.Metric) {
    values := cc.ClusterManager.ReallyExpensiveAssessmentOfTheSystemState()

    for key, value := range values {
        ch <- prometheus.MustNewConstMetric(
            valueDesc,
            prometheus.CounterValue,
            value,
            key,
        )
    }
}