Bulk create Cloudwatch alarms for 4xx/5xx API Gateway errors. Tweak for your needs.

main.go

package main

import (
	"fmt"
	"log"
	"strings"

	"github.com/aws/aws-sdk-go/aws"
	"github.com/aws/aws-sdk-go/aws/session"
	"github.com/aws/aws-sdk-go/service/cloudwatch"
)

const (
	Error4xx = "4XXError"
	Error5xx = "5XXError"
)

type API struct {
	Name   string
	Stages []Stage
}

type Stage struct {
	Name         string
	Threshold4xx int64
	Threshold5xx int64
}

var SNSARN = "arn:aws:sns:eu-west-1:<account>:<snsname>"

var apis = []API{
	{
		Name: "api",
		Stages: []Stage{
			{
				Name:         "staging",
				Threshold4xx: 0,
        Threshold5xx: 0,
			},
			{
				Name:         "production",
				Threshold4xx: 20,
        Threshold5xx: 0,
			},
		},
	},
}

func main() {
	var err error
	svc := cloudwatch.New(session.New())

	for _, api := range apis {
		for _, stage := range api.Stages {
			input4xx := makeInput(api.Name, stage.Name, Error4xx, stage.Threshold4xx)
			_, err = svc.PutMetricAlarm(input4xx)
			if err != nil {
				log.Fatalf("Error creating %s %s 4xx: %v", api.Name, stage.Name, err)
			}

			input5xx := makeInput(api.Name, stage.Name, Error5xx, stage.Threshold5xx)
			_, err = svc.PutMetricAlarm(input5xx)
			if err != nil {
				log.Fatalf("Error creating %s %s 5xx: %v", api.Name, stage.Name, err)
			}
		}

	}
}

func makeInput(api string, stage string, metric string, threshold int64) *cloudwatch.PutMetricAlarmInput {
	description := "Any"
	if threshold > 0 {
		description = "Elevated"
	}

	description = fmt.Sprintf("%s %s on %s [%s]", description, metric, api, stage)

	return &cloudwatch.PutMetricAlarmInput{
		AlarmActions:       []*string{aws.String(SNSARN)},
		AlarmDescription:   aws.String(description),
		AlarmName:          aws.String(fmt.Sprintf("apigateway-%s-%s-%s", api, stage, strings.ToLower(metric))),
		ComparisonOperator: aws.String("GreaterThanThreshold"),
		Dimensions: []*cloudwatch.Dimension{
			{
				Name:  aws.String("ApiName"),
				Value: aws.String(api),
			},
			{
				Name:  aws.String("Stage"),
				Value: aws.String(stage),
			},
		},
		EvaluationPeriods: aws.Int64(1),
		MetricName:        aws.String(metric),
		Namespace:         aws.String("AWS/ApiGateway"),
		Period:            aws.Int64(60),
		Statistic:         aws.String("Sum"),
		Threshold:         aws.Float64(float64(threshold)),
		TreatMissingData:  aws.String("notBreaching"),
		Unit:              aws.String("Count"),
	}
}