A suite of Go utilities for AWS Lambda functions to ease adopting best practices.

• Event decapsulation: Parse event data received when invoking. Also golambda make easy to write unit test of Lambda function
• Structured logging: golambda provides requisite minimum logging interface for Lambda function. It output log as structured JSON.
• Error handling: Error structure with arbitrary variables and stack trace feature.
• Get secret parameters: Secret values should be stored in AWS Secrets Manager and can be got easily.

NOTE: The suite is NOT focusing to Lambda function for API gateway, but partially can be leveraged for the function.

$ go get github.com/m-mizutani/golambda/v2

Lambda function can have event source(s) such as SQS, SNS, etc. The main data is encapsulated in their data structure. golambda provides not only decapsulation feature for Lambda execution but also encapsulation feature for testing. Following event sources are supported for now.

• SQS body: DecapSQS
• SNS message: DecapSNS
• SNS message over SQS: DecapSNSoverSQS

package main

import (
	"strings"

	"github.com/m-mizutani/golambda/v2"
)

// MyEvent is exported for test
type MyEvent struct {
	Message string `json:"message"`
}

// Handler is exported for test
func Handler(ctx context.Context, event *golambda.Event) (string, error) {
	// Decapsulate body message(s) in SQS Event structure
	events, err := event.DecapSQS()
	if err != nil {
		return "", err
	}

	var response []string
	// Iterate body message(S)
	for _, ev := range events {
		var msg MyEvent
		// Unmarshal golambda.Event to MyEvent
		if err := ev.Bind(&msg); err != nil {
			return "", err
		}

		// Do something
		response = append(response, msg.Message)
	}

	return strings.Join(response, ":"), nil
}

func main() {
	golambda.Start(Handler)
}

package main_test

import (
	"testing"

	"github.com/m-mizutani/golambda/v2"
	"github.com/stretchr/testify/require"

	main "github.com/m-mizutani/golambda/v2/example/decapEvent"
)

func TestHandler(t *testing.T) {
	messages := []main.MyEvent{
		{
			Message: "blue",
		},
		{
			Message: "orange",
		},
	}
	event, err := golambda.NewSQSEvent(messages)
	require.NoError(t, err)

	resp, err := main.Handler(event)
	require.NoError(t, err)
	require.Equal(t, "blue:orange", resp)
}

Lambda function output log data to CloudWatch Logs by default. CloudWatch Logs and Insights that is rich CloudWatch Logs viewer supports JSON format logs. Therefore JSON formatted log is better for Lambda function.

golambda provides Logger for JSON format logging. It has With() to add a pair of key and value to a log message. Logger has lambda request ID by default if you use the logger with golambda.Start(). Logger is provided as zlog.Logger. RenewLogger() allows you to reconfigure logging setting.

v1 := "say hello"
golambda.Logger.With("var1", v1).Info("Hello, hello, hello")
/* Output:
{
	"level": "info",
	"lambda.requestID": "565389dc-c13f-4fc0-b113-xxxxxxxxxxxx",
	"time": "2020-12-13T02:44:30Z",
	"var1": "say hello",
	"message": "Hello, hello, hello"
}
*/

golambda.Logger (golambda.LambdaLogger type) provides following log level. Log level can be configured by environment variable LOG_LEVEL.

• TRACE
• DEBUG
• INFO
• WARN
• ERROR

Lambda function should return error to top level function when occurring unrecoverable error, should not exit suddenly. Therefore PANIC and FATAL is not provided according to the thought.

NOTE: golambda.Error is obsoleted and use github.com/m-mizutani/goerr instead.

golambda.Error can have pairs of key and value to keep context of error. For example, golambda.Error can bring original string data when failed to unmarshal JSON. The string data can be extracted in caller function.

Also, golambda.Start supports general error handling:

1. Output error log with
   • Pairs of key and value in goerr.Error of goerr as error.values
   • Stack trace of error as error.stacktrace
2. Send error record to sentry.io if SENTRY_DSN is set as environment variable
   • Stack trace of golambda.Error is also available in sentry.io by compatibility with github.com/pkg/errors
   • Output event ID of sentry to log as error.sentryEventID
   • You can set SENTRY_ENV and SENTRY_RELEASE also optionally.

package main

import (
	"github.com/m-mizutani/golambda/v2"
)

// Handler is exported for test
func Handler(event golambda.Event) (interface{}, error) {
	trigger := "something wrong"
	return nil, goerr.New("oops").With("trigger", trigger)
}

func main() {
	golambda.Start(Handler)
}

Then, golambda output following log to CloudWatch.

{
    "level": "error",
    "lambda.requestID": "565389dc-c13f-4fc0-b113-f903909dbd45",
    "trigger": "something wrong",
    "stacktrace": [
        {
            "func": "main.Handler",
            "file": "xxx/your/project/src/main.go",
            "line": 27
        },
        {
            "func": "github.com/m-mizutani/golambda.Start.func1",
            "file": "xxx/github.com/m-mizutani/golambda/lambda.go",
            "line": 107
        }
    ],
    "time": "2020-12-13T02:42:48Z",
    "message": "oops"
}

In general, parameters of Lambda function are stored sa environment variable, such as LOG_LEVEL. However secret parameters such as credential, API key/token, etc should be stored in AWS Secrets Manager or Parameter Store to control access permission more explicitly in many cases.

golambda.GetSecretValues fetches values of AWS Secrets Manager and binds to a structure variable.

type mySecret struct {
    Token string `json:"token"`
}
var secret mySecret
if err := golambda.GetSecretValues(os.Getenv("SECRET_ARN"), &secret); err != nil {
    log.Fatal("Failed: ", err)
}

// Access to other service with secret.Token

See LICENSE.