humank / lambda-saga-pattern

By using AWS StepFunction and Lambda Function, it's an easy way to deal with distributed transactions among microservices.

lambda-saga-pattern

Implements the Saga pattern for Lambda functions using Step Functions.

The example is based on Catie McCaffrey's example in her talk on Applying the Saga pattern.

Each request has a compensating request for rollback.

The Saga goes like this:

Begin saga
  Start book hotel request
  End book hotel request
  Start book flight request
  End book flight request
  Start book car rental request
  End book car rental request  
End saga

We'll need a transaction log for the saga, and Step Functions would be our coordinator for the saga.

Because the compensating requests can also fail so we need to be able to retry them until success, which means they have to be idempotent.

This demo implements backward recovery only.

For forward recovery you also need to ensure the requests are imdempotent.

The code for the corresponding Step Function is here.

Setup AWS environment

Create Step Function Execution Role

It could be a service role or self defined one, which contains the following policy :

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Action": [
                "lambda:InvokeFunction"
            ],
            "Resource": "*"
        }
    ]
}

Modify execution script

All the scripts default run in us-west-2. If you'd like to deploy to different region, make sure the following files are also modified.

• runtest.sh
• deploy-stepfunc.sh

you need to replace real aws account id in the previous script files. Besides, replace the execution role in deply-stepfunc.sh

Replace "ROLEARN" with you created one.

Lambda Function Deployment

This serverless lambda function is developing with Serverless Framework adopted.

To deploy this example to an AWS environment, run:

./build.sh deploy <stage> <region> <aws_profile>

example

/build.sh deploy dev us-west-2 default

which will install NPM packages and use the Serverless framework to deploy both DynamoDB tables as well as Lambda functions to the account.

To remove the demo, run:

./build.sh remove <stage> <region> <aws_profile>

Deploy Step Functions

./deploy-stepfunc.sh

Run Test

Try success scenario

/runtest.sh test-booking-success.json

Try compensate scenario

/runtest.sh test-booking-fail.json