Lambda as orchestrator

Many business workflows result in complex workflow logic, where the flow of operations depends on multiple factors. In an ecommerce example, a payments service is an example of a complex workflow:

• A payment type may be cash, check, or credit card, all of which have different processes.

• A credit card payment has many possible states, from successful to declined.

• The service may need to issue refunds or credits for a portion or the entire amount.

• A third-party service that processes credit cards may be unavailable due to an outage.

• Some payments may take multiple days to process.

Implementing this logic in a Lambda function can result in ‘spaghetti code’ that’s difficult to read, understand, and maintain. It can also become very fragile in production systems. The complexity is compounded if you must handle error handling, retry logic, and inputs and outputs processing. These types of orchestration functions are an anti-pattern in Lambda-based applications.

Instead, use AWS Step Functions to orchestrate these workflows using a versionable, JSON-defined state machine. State machines can handle nested workflow logic, errors, and retries. A workflow can also run for up to 1 year, and the service can maintain different versions of workflows, allowing you to upgrade production systems in place. Using this approach also results in significantly less custom code, making an application easier to test and maintain.

While Step Functions is designed for workflows within a bounded context or microservice, to coordinate state changes across multiple services, instead use Amazon EventBridge. This is a serverless event bus that routes events based upon rules, and simplifies orchestration between microservices.