Test Go Lambda locally with AWS Serverless Application Model and localstack

Question

I am trying to test locally a lambda function that is listing buckets on a S3 bucket.

To have a local S3 bucket for my test, I use localstack:

docker run --rm -it -p 4566:4566 -p 4510-4559:4510-4559 localstack/localstack

I can then create a bucket (it works):

aws s3api --endpoint-url=http://localhost:4566  --region us-east-1 create-bucket --bucket images

Then I have a lambda that tries to connect to S3 and list the buckets:

package s3

import (
    "context"
    "github.com/aws/aws-sdk-go-v2/aws"
    "github.com/aws/aws-sdk-go-v2/config"
    awsS3 "github.com/aws/aws-sdk-go-v2/service/s3"
    "fmt"
    "log"
)

type S3ListBucketsAPI interface {
    ListBuckets(ctx context.Context,
        params *awsS3.ListBucketsInput,
        optFns ...func(*awsS3.Options)) (*awsS3.ListBucketsOutput, error)
}

func GetAllBuckets(c context.Context, api S3ListBucketsAPI, input *awsS3.ListBucketsInput) (*awsS3.ListBucketsOutput, error) {
    return api.ListBuckets(c, input)
}

func New(bucketName string) () {
    awsEndpoint := "http://localhost:4566"
    awsRegion := "us-east-1"
  
    customResolver := aws.EndpointResolverFunc(func(service, region string) (aws.Endpoint, error) {
      if awsEndpoint != "" {
        return aws.Endpoint{
          PartitionID:   "aws",
          URL:           awsEndpoint,
          SigningRegion: awsRegion,
          HostnameImmutable: true,
        }, nil
      }
  
      return aws.Endpoint{}, &aws.EndpointNotFoundError{}
    })
  
    cfg, err := config.LoadDefaultConfig(context.TODO(),
      config.WithRegion(awsRegion),
      config.WithEndpointResolver(customResolver),
    )
    if err != nil {
      log.Fatalf("Cannot load the AWS configs: %s", err)
    }

    client := awsS3.NewFromConfig(cfg)

    input := &awsS3.ListBucketsInput{}

    result, err := GetAllBuckets(context.TODO(), client, input)
    if err != nil {
        fmt.Println(err)
    }

    for _, bucket := range result.Buckets {
        fmt.Println(*bucket.Name + ": " + bucket.CreationDate.Format("2006-01-02 15:04:05 Monday"))
    }
}

To test my lambda locally I use SAM. Here is the template:

AWSTemplateFormatVersion : '2010-09-09'
Transform: AWS::Serverless-2016-10-31
Description: AdBannerLambda
Resources:
  BucketListLambda:
    Type: AWS::Serverless::Function
    Properties:
      Handler: bin/bucket-list-lambda
      Runtime: go1.x
      Timeout: 100
      Policies:
        - S3FullAccessPolicy

When I execute the lambda:

sam local invoke AdBannerLambda  -e test_data/payload.json

I have this error:

START RequestId: 7c9da60f-9a68-476b-bcd8-c24da422e80c Version: $LATEST
Got an error retrieving buckets:
operation error S3: ListBuckets, exceeded maximum number of attempts, 3, https response error StatusCode: 0, RequestID: , HostID: , request send failed, Get "http://localhost:4566/": dial tcp 127.0.0.1:4566: connect: connection refused
2022/07/28 14:54:10 <nil>
28 Jul 2022 14:54:10,979 [ERROR] (rapid) Init failed error=Runtime exited with error: exit status 1 InvokeID=
END RequestId: 5319d88f-ea30-4a61-adb6-e9ab4a83c17e

My lambda cannot reach the S3 bucket in my localstack docker even though the same code in a simple go file (not a lambda) can perform actions on S3. Any idea where the problem comes from?

Test Go Lambda locally with AWS Serverless Application Model and localstack

0 Answers0