cloudwatch-to-mackerel

main.go

package main

import (
	"context"
	"encoding/json"
	"errors"
	"log"
	"os"
	"time"

	"github.com/aws/aws-lambda-go/events"
	"github.com/aws/aws-lambda-go/lambda"
	"github.com/aws/aws-sdk-go/aws"
	"github.com/aws/aws-sdk-go/aws/session"
	"github.com/aws/aws-sdk-go/service/cloudwatch"
	mackerel "github.com/mackerelio/mackerel-client-go"
)

const MaxMetricValues = 100

func main() {
	lambda.Start(handler)
}

func handler(ctx context.Context, event *events.AutoScalingEvent) error {
	var qs []*cloudwatch.MetricDataQuery
	f, err := os.Open(os.Getenv("QUERY_FILE"))
	if err != nil {
		return err
	}
	if err := json.NewDecoder(f).Decode(&qs); err != nil {
		return err
	}

	svc := cloudwatch.New(session.Must(session.NewSession(&aws.Config{})))
	now := time.Now()
	service := os.Getenv("SERVICE")
	if service == "" {
		return errors.New("SERVICE required")
	}
	apiKey := os.Getenv("MACKEREL_APIKEY")
	if apiKey == "" {
		return errors.New("MACKEREL_APIKEY required")
	}

	res, err := svc.GetMetricData(&cloudwatch.GetMetricDataInput{
		StartTime:         aws.Time(now.Add(-3 * time.Minute)),
		EndTime:           aws.Time(now),
		MetricDataQueries: qs,
	})
	if err != nil {
		return err
	}

	client := mackerel.NewClient(apiKey)
	values := make([]*mackerel.MetricValue, 0, MaxMetricValues)

	for _, r := range res.MetricDataResults {
		for i, ts := range r.Timestamps {
			label, ts, value := *r.Label, (*ts).Unix(), *(r.Values[i])
			values = append(values, &mackerel.MetricValue{
				Name:  label,
				Time:  ts,
				Value: value,
			})
			if len(values) >= MaxMetricValues {
				if err := client.PostServiceMetricValues(service, values); err != nil {
					log.Println("[warn] failed to post to Mackerel", err)
				} else {
					log.Printf("[info] %d metric values posted", len(values))
				}
				values = values[0:0]
			}
		}
	}
	if len(values) > 0 {
		if err := client.PostServiceMetricValues(service, values); err != nil {
			return err
		} else {
			log.Printf("[info] %d metric values posted", len(values))
		}
	}
	return nil
}