Example Python AWS SNS Consumer

(latest pact)

(prod/prod pact)

This is an example of a Python AWS SNS consumer that uses Pact, Pactflow and GitHub Actions to ensure that it is compatible with the expectations its consumers have of it.

All examples in the series example-consumer-<language>-sns provide the same functionality to be easily comparable across languages. As such, please refer to [https://docs.pactflow.io/docs/examples/aws/sns/consumer/](AWS SNS Consumer Examples) to avoid unnecessary duplication of details here.

Language specific sections which differ from the canonical example only can be found below.

How to write tests?

We recommend that you split the code that is responsible for handling the protocol specific things - in this case the lambda and SNS input - and the piece of code that actually handles the payload.

You're probably familiar with layered architectures such as Ports and Adaptors (also referred to as a Hexagonal architecture). Following a modular architecture will allow you to do this much more easily:

This code base is setup with this modularity in mind:

• Lambda Handler
• Event Service
• Business Logic
  • Product
  • Repository

The target of our consumer pact test is the Event Service, which is responsible for consuming a Product update event, and persisting it to a database (the Repository).

See also:

• https://dius.com.au/2017/09/22/contract-testing-serverless-and-asynchronous-applications/
• https://dius.com.au/2018/10/01/contract-testing-serverless-and-asynchronous-applications---part-2/

Usage

Testing

• Run the unit tests: make test
• Run a (local) lambda integration test: make integration

Running

• Deploy the actual app: make deploy (see below for more background)
• Publish a test event: make publish
• View the lambda logs: make logs

Here is some sample output publishing and viewing the logs:

➜  example-consumer-js-sns git:(master) ✗ npm run publish                                                                                                                                                                                                                                                    <aws:pact-dev>

> product-service@1.0.0 publish /Users/matthewfellows/development/public/example-consumer-js-sns
> ./scripts/publish.sh

finding topic
have topic: arn:aws:sns:ap-southeast-2:838728264948:pactflow-example-consumer-js-sns-ProductEvent-144XVHN8QP2D3, publishing message
{
    "MessageId": "735a2daa-7eaa-53d7-b362-75b0d9227708"
}

> product-service@1.0.0 logs /Users/matthewfellows/development/public/example-consumer-js-sns
> sam logs -n ProductEventHandler --stack-name pactflow-example-consumer-js-sns -t

2020/11/03/[$LATEST]df9d6b71ef1e49789f4ebca64fc19270 2020-11-03T00:25:24.984000 START RequestId: 47e97e7d-52cf-4c83-9133-545749ed2750 Version: $LATEST
2020/11/03/[$LATEST]df9d6b71ef1e49789f4ebca64fc19270 2020-11-03T00:25:25.012000 2020-11-03T00:25:24.988Z	47e97e7d-52cf-4c83-9133-545749ed2750	INFO	{
  Records: [
    {
      EventSource: 'aws:sns',
      EventVersion: '1.0',
      EventSubscriptionArn: 'arn:aws:sns:ap-southeast-2:838728264948:pactflow-example-consumer-js-sns-ProductEvent-144XVHN8QP2D3:efaf0845-3847-4b5d-a4b1-68f33ef524e8',
      Sns: [Object]
    }
  ]
}
2020/11/03/[$LATEST]df9d6b71ef1e49789f4ebca64fc19270 2020-11-03T00:25:25.032000 END RequestId: 47e97e7d-52cf-4c83-9133-545749ed2750
2020/11/03/[$LATEST]df9d6b71ef1e49789f4ebca64fc19270 2020-11-03T00:25:25.032000 REPORT RequestId: 47e97e7d-52cf-4c83-9133-545749ed2750	Duration: 48.28 ms	Billed Duration: 100 ms	Memory Size: 128 MB	Max Memory Used: 64 MB	Init Duration: 136.98 ms

If you edit the file ./scripts/publish.sh to remove a valid property, or upload invalid JSON you will get something like this:

2020/11/03/[$LATEST]df9d6b71ef1e49789f4ebca64fc19270 2020-11-03T00:36:23.376000 2020-11-03T00:36:23.376Z	3eb496cd-c663-4ae2-a717-8f261b7ad48c	ERROR	Invoke Error 	{"errorType":"AssertionError","errorMessage":"id is a mandatory field","code":"ERR_ASSERTION","generatedMessage":false,"expected":true,"operator":"==","stack":["AssertionError [ERR_ASSERTION]: id is a mandatory field","    at new Product (/var/task/src/product/product.js:5:5)","    at handler (/var/task/src/product/product.handler.js:7:23)","    at /var/task/src/service/product.js:10:44","    at Array.map (<anonymous>)","    at Runtime.lambda [as handler] (/var/task/src/service/product.js:10:33)","    at Runtime.handleOnce (/var/runtime/Runtime.js:66:25)"]}
2020/11/03/[$LATEST]df9d6b71ef1e49789f4ebca64fc19270 2020-11-03T00:36:23.416000 END RequestId: 3eb496cd-c663-4ae2-a717-8f261b7ad48c
2020/11/03/[$LATEST]df9d6b71ef1e49789f4ebca64fc19270 2020-11-03T00:36:23.416000 REPORT RequestId: 3eb496cd-c663-4ae2-a717-8f261b7ad48c	Duration: 75.82 ms	Billed Duration: 100 ms	Memory Size: 128 MB	Max Memory Used: 65 MB