LocalStack Tutorial

💻 A fully functional local AWS cloud stack.�Develop and test your cloud & Serverless apps offline!

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Waldemar Hummer

waldemar.hummer@gmail.com

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WeAreDevelopers World Congress

Berlin, June 2019

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What is LocalStack?

• Framework that allows local testing of Cloud applications
• Stubs out AWS services on the local machine (currently 22 services supported)

• API Gateway at http://localhost:4567
• Kinesis at http://localhost:4568
• DynamoDB at http://localhost:4569
• DynamoDB Streams at http://localhost:4570
• Elasticsearch at http://localhost:4571
• S3 at http://localhost:4572
• Firehose at http://localhost:4573
• Lambda at http://localhost:4574
• SNS at http://localhost:4575
• SQS at http://localhost:4576
• Redshift at http://localhost:4577

• ES (Elasticsearch Service) at http://localhost:4578
• SES at http://localhost:4579
• Route53 at http://localhost:4580
• CloudFormation at http://localhost:4581
• CloudWatch at http://localhost:4582
• SSM at http://localhost:4583
• SecretsManager at http://localhost:4584
• StepFunctions at http://localhost:4585
• CloudWatch Logs at http://localhost:4586
• STS at http://localhost:4592
• IAM at http://localhost:4593

History

• Started as a small project at Atlassian (Sydney) in late 2016
• Jeff Barr (Chief Evangelist @ AWS) tweeted about LocalStack in March 2017
• https://twitter.com/jeffbarr/�status/846382903210663936

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• Meanwhile has turned into a flagship open source project
• 17.000 stars on Github
• Several third party projects depending on LocalStack
• Upgrade to “Adopt” in the ThoughtWorks Technology Radar:
• https://www.thoughtworks.com/radar/tools/localstack

Architecture

• Focus on modularity and pluggability
• Choose best-of-breed implementation for each service
• https://github.com/spulec/moto/
• https://github.com/mhart/kinesalite
• https://docs.aws.amazon.com/�amazondynamodb/latest/�developerguide/DynamoDBLocal.html
• ...
• Proxy based access to backend services
• Can be started either locally or in Docker

LocalStack main process (Python)

DynamoDB Local backend

(port 4564)

DynamoDB proxy (port 4569)

S3 moto backend

(port 4563)

S3 proxy�(port 4572)

Lambda API�(port 4574)

Kinesis proxy�(port 4568)

Kinesis backend

(port 4565)

...

CloudFormation API (port 4574)

Recent Growth

• Docker pulls of the localstack/localstack image
• Apprx 5 million total Docker image pulls to date

Configuration Options (excerpt)

• SERVICES: Comma-separated list of services to start (e.g., “sqs,sns,s3,es”)
• HOSTNAME / HOSTNAME_EXTERNAL: Customize the host names
• LAMBDA_EXECUTOR: One of “local”, “docker”, or “docker-reuse”
• LAMBDA_REMOTE_DOCKER: Whether Lambdas are run in remote Docker
• USE_SSL: Whether to start APIs with SSL enabled (self-signed or own certs)
• *_ERROR_PROBABILITY: For injecting faults into Kinesis/DynamoDB APIs
• DATA_DIR: Local directory for saving persistent data
• DOCKER_FLAGS: Pass custom flags to “docker run …” for Lambdas
• LAMBDA_FALLBACK_URL: Fallback URL if non-existing Lambda is invoked

Using the Command Line

• Command-Line Interface “awslocal”
• https://github.com/localstack/awscli-local
• Automatically sets the http://localhost:XXXX endpoints for LocalStack services
• Example: Put a message on an SQS queue
• awslocal sqs create-queue --queue-name q1
• awslocal sqs send-message� --queue-url http://localhost:4576/queue/q1� --message-body 'hello world'
• awslocal sqs receive-message� --queue-url http://localhost:4576/queue/q1

Demo Application

• Create a simple application that simulates processing of long-running requests on AWS
• Application is defined and deployed using the Serverless framework: http://serverless.com/
• Make use of various AWS services:
• API Gateway
• Cloud Formation
• Dynamo DB
• Lambda
• S3
• SQS
• Step Functions

QUEUED

PROCESSING

FINISHED

Demo Application - Architecture

LocalStack

Step Functions State Machine

Application Handler Lambda

API Gateway

REST API

Processing Lambda

Request Worker Lambda

DynamoDB Table

Archiving Lambda

S3 Bucket

User’s Web Browser

Live Coding

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https://github.com/whummer/localstack-demo

Running in Docker

• Can run in practically any environment (“zero” requirements)
• Main process and Lambda functions run in Docker
• Mounting Lambda code into containers enables a quick dev loop

Host (e.g., Mac OS)

Docker

/path/to/lambda/handler.py

LocalStack container

Lambda container 1

/path/to/handler.py

Lambda API

mount

Conclusion

• Developing cloud apps locally is feasible!
• Allows for a very efficient dev&test loop
• Offline testing
• Zero costs
• No name collisions with multiple developers
• Caveat: Not always 100% the same conditions as in the real environment
• Integration testing on AWS still required before pushing changes out to production
• Future plans
• Single entry point - proxy all APIs on a single port, instead of one port per service
• Enable DNS resolution for custom domain names (e.g., S3 bucket names)
• Support for more cloud APIs
• Extend the scope beyond AWS
• Azure Cloud, Google Cloud Platform, IBM Bluemix
• Improve the performance and reduce the memory footprint of the stack