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Price Migration Engine - Lambdas

Code structure

The codebase is structured to keep a clear separation between pure and effectful code. (Effectful has different meanings, but I mean by it having side-effects or not pure.)

The model package holds all the pure code in the project. All code here is deterministic. It neither generates nor depends on any kind of real-world effect; including random numbers, relative dates, logging or printing to console.

The effects of the code are generated and consumed through services, following the ZIO convention. Each service has a type, an interface and at least one implementation. For example, the Zuora type, and live implementation.

These services are composed together into ZIO vertical and horizontal layers, and these layers form the runtime environment for each of the lambdas by compile-time dependency injection. A vertical layer is one in which one service depends on another: they are related together by the >>> operator. In a horizontal layer, two peer services are related together by the ++ operator. For a more detailed explanation of how these layers work, see the ZIO documentation.

The lambdas are all in the handlers package.

All the dependencies of the project have been chosen for their light weight and minimal number of transitive dependencies, so that the artefact generated is of minimal size and lambdas can warm up quickly.

The same generated jar is used by all the lambdas. The only variation in their deployment is the configuration of the main endpoint.

To run lambdas locally in Intellij

You can run or debug any of the lambdas in any deployment environment from Intellij.
You will need up-to-date AWS credentials stored locally. Set up a run configuration for the lambda, using the following environment variables:

  • AWS_PROFILE=profileName
  • stage=DEV|CODE|PROD

and also the specific environment variables for the lambda you are running.

Environment variables

The environment variables set in the lambdas are provided by Secrets Manager and can also be changed manually in the AWS console by navigating to the lambda (e.g.: price-migration-engine-estimation-lambda-CODE) > Configuration > Environment variables

Note: The DEV and CODE environments both currently point to apisandbox.zuora.com.

We have a copy of our production Zuora environment, the "centralsandbox" (which we access via test.zuora.com). However, as we do not have an equivalent salesforce environment set up, we cannot run the step function from start to finish with this environment.

Individual lambdas like the EstimationLambda and the AmendmentLambda can be run against this Zuora environment if we want to test on subscriptions in production. See how to run the lambdas locally with the necessary environment variables (see above).

Environment variables for EstimationHandler and Amendment Handler

  • input=The input cohort spec in JSON string format (see below for example)
  • batchSize=batchSize
  • zuoraApiHost=host
  • zuoraClientId=personal clientId
  • zuoraClientSecret=personal clientSecret

Input Cohort Spec Example

{
  "cohortName": "EchoLegacyTesting",
  "brazeName": "cmp123",
  "earliestAmendmentEffectiveDate": "2022-08-02"
}

Note the above is different to the input JSON that the lambda admits