Localstack with terraform

With my recent projects, I’ve been working more and more with terraform. LocalStack is a collection of AWS-compatible services you can run yourself. It’s meant for development and testing, not as a target to host real production instances of your application.

It doesn’t cover 100% of the AWS alphabet soup, but it implements many of the most popular services.

Today, I want to show you how to setup a few simple resources and deploy a lambda to Localstack using just your local setup.

---

All of the examples below are in the repository.

The first todo, was to configure and create a Localstack yml file.

services:
  localstack:
    image: localstack/localstack:0.11.4
    ports:
      - "4567-4597:4567-4597"
      - "${PORT_WEB_UI-8080}:${PORT_WEB_UI-8080}"
    environment:
      - SERVICES=s3,iam,lambda
      - DEBUG=${DEBUG- }
      - DATA_DIR=${DATA_DIR- }
      - PORT_WEB_UI=${PORT_WEB_UI- }
      - LAMBDA_REMOTE_DOCKER=0
      - LAMBDA_EXECUTOR=${LAMBDA_EXECUTOR- }
    volumes:
      - "${TMPDIR:-/tmp/localstack}:/tmp/localstack"
      - "/var/run/docker.sock:/var/run/docker.sock"

With this, we can start a local version of the s3, iam and lambda services. Just with one command: docker-compose up -d .

The lambda itself is simple. One of my previous kata methods packaged into a zip file. It was a bit annoying though, that AWS lambda still does not support python 3.9+.

After zipping it, deploying to localstack is simple:

terraform init -input=false
terraform apply -auto-approve -input=false

It will deploy all definitions stored in local.tf file. All it takes is to properly configure the provider:

provider "aws" {
  access_key                  = "mock_access_key"
  region                      = "eu-west-1"
  s3_force_path_style         = true
  secret_key                  = "mock_secret_key"
  skip_credentials_validation = true
  skip_metadata_api_check     = true
  skip_requesting_account_id  = true

  endpoints {
    s3     = "http://localhost:4572"
    lambda = "http://localhost:4574"
    iam    = "http://localhost:4593"
  }
}

Once you’ll checkout the project, just go through make all. And the resulting tests were so satisfactory:

aws --endpoint-url=http://localhost:4572 s3 ls
2021-07-17 15:12:23 example-bucket
aws --endpoint-url=http://localhost:4574 lambda list-functions
{
    "Functions": [
        {
            "FunctionName": "lowest-common-ancestor-localstack",
            "FunctionArn": "arn:aws:lambda:us-east-1:000000000000:function:lowest-common-ancestor-localstack",
            "Runtime": "python3.8",
            "Role": "arn:aws:iam::000000000000:role/example_lambda",
            "Handler": "program.lambda_handler",
            "CodeSize": 924,
            "Description": "lowest-common-ancestor-localstack",
            "Timeout": 3,
            "MemorySize": 128,
            "LastModified": "2021-07-17T14:12:23.922+0000",
            "CodeSha256": "gToFEYreRpfgFMM7mMBq4qZSK2MWoloTh002s7l1fMQ=",
            "Version": "$LATEST",
            "VpcConfig": {},
            "Environment": {
                "Variables": {
                    "DATA_BUCKET": "example-bucket"
                }
            },
            "TracingConfig": {
                "Mode": "PassThrough"
            },
            "RevisionId": "fef04191-8ce8-4b87-9da4-f7c2f7b2d2e2",
            "State": "Active",
            "LastUpdateStatus": "Successful"
        }
    ]
}

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I meant to work a bit on principles.green this week. I failed. I will try to come back to this in some time. For now, I intend to work some more with localstack and python tests.