README.md

Go crypto operations are super slow on AWS lambda while processing an event, but they are super fast during cold start.

The performance is pretty reliably loke the following:

$ aws lambda invoke --function-name $FUNCTION response.json
$ jq -r < response.json
cold start: count: 10
cold start: total dur: 143.704664ms
cold start: avg dur 14.370466ms
count: 10
total dur: 1.973332046s
avg dur 197.333204ms

main.go

package main

import (
	"bytes"
	"context"
	"fmt"
	"github.com/aws/aws-lambda-go/lambda"
	"github.com/dgrijalva/jwt-go"
	"time"
)

var pk = []byte("-----BEGIN EC PRIVATE KEY-----\nMIHcAgEBBEIBkhuWYSdLeZkeKFskbnfAzmecetbNEe95CvS3txBAF+TinQtjluUN\nttbwVDyhNRY7uEJH5CKtaNABRojzU2KwhwagBwYFK4EEACOhgYkDgYYABAHEvCZg\nbsuBQxPy8c3Rki1EG3dfDw5aWurBKeq2QoFcke2Dx8usTz0KtQBKKGrC8SukZdYh\nsR8wBe/hGbqPxnaizQDIcmC5bDxWTkTP2ugPxd+ia8fTAkIoFhiJHg7Iv3Cpr5Wd\nne13zsG54ZlpJY1cRqgNZFuClRt26ZgIgg8AfV3c0A==\n-----END EC PRIVATE KEY-----")

func whyIsThisSlow(count int) time.Duration {
	startTime := time.Now()
	for i := 0 ; i < count; i++ {
		if _, err := jwt.ParseECPrivateKeyFromPEM(pk); err != nil {
			panic(err)
		}
	}
	return time.Now().Sub(startTime)
}


func main() {
	const coldStartCount = 10
	coldStartDuration := whyIsThisSlow(coldStartCount)

	lambda.Start(func (context.Context) (string, error) {
		w := bytes.NewBuffer(nil)

		const count = 10
		duration := whyIsThisSlow(count)

		fmt.Fprintf(w, "cold start: count: %d\n", coldStartCount)
		fmt.Fprintf(w, "cold start: total dur: %s\n", coldStartDuration)
		fmt.Fprintf(w, "cold start: avg dur %s\n", coldStartDuration / coldStartCount)

		fmt.Fprintf(w, "count: %d\n", count)
		fmt.Fprintf(w, "total dur: %s\n", duration)
		fmt.Fprintf(w, "avg dur %s\n", duration / count)

		return w.String(), nil
	})
}