AWS Lambda Article Processor

This repo contains A test app that attempts to recreate concepts from actor model design patterns in Lambda. The focus is on lambda rather than the on the programming language itself. I have chosen Python because it gives a quicker feedback loop and shorter cold start time.

Motivation

I have had experience working with Akka Actor model, and I feel that there is some degree of resemblance between lambda functions and stateless actors. However, I need to understand more to be able to draw that comparison. TDD'ing, writing and deploying actors is rather simple in Scala. I am curious if the same can be achieved with AWS lambda.

Design consideration

I am going to treat each lambda as a stateless actor. It should be able to do one thing only (from domain perspective) and do it very well.

Domain

For this exercise, I am assuming that I want to go through a hypothetical collection or a stream of articles. Each article has the following fields

• author
• content
• priority

The operations I am going to perform

1. Validate that a record has an author name attached, if not attach an error code

2. Count the number of words in the content

3. At the same time

   • Capitalize the first letter of each word of the author name

   • Add five to the rating (this channel has higher rating compared to other channels)

Implementation

Lambda Functions and Step Function State Machine are used together to create a pipeline that resembles the implementation mentioned above.

Deployment pipeline

[pipeline.yaml] is a CloudFormation template that creates our three stages deployment. Those are Source, Build and Deploy.

Source stage picks up the source code from Github (this repo).

Build runs the [buildspec.yml] file, which in turn runs the unit tests and packages our application (I think in the future, this should be two separate stages)

Deploy Creates and executes [template.yml] CloudFormation template. The template includes both the definition of the lambda functions and the state machine definition.

Notes

State machine definition within template.yml

I find embedding FSM JSON definition into [template.yml] YAML template to be very annoying. I couldn't find a way to import the FSM definition from a separate file. I am considering using a script to embed JSON into the template in the build stage in the future and keep both separated. Currently, they look like this:

Properties:
  DefinitionString:
    !Sub
      - |-
        {
          "Comment": "Article Processing State Machine",
          "StartAt": "InspectEmptyAuthor",
          "States": {
            "InspectEmptyAuthor": {
              "Type": "Task",
              "Resource": "${inspectEmptyAuthorFunctionArn}",
              "Next" :"ContentLength"
            },
            "ContentLength": {
              "Type": "Task",
              "Resource": "${contentLengthFunctionArn}",
              "End": true
            }
          }
        }
      - {inspectEmptyAuthorFunctionArn: !GetAtt [ InspectEmptyAuthorFunction, Arn ], contentLengthFunctionArn: !GetAtt [ ContentLengthFunction, Arn ]}

Todo:

• Create a unit test that resembles the pipeline.
• Create an end-to-end test because unit tests are not enough.
• Implement a more complicated workflow including a State Machine (we only use the state machine here to glue Lambdas)