New pattern: apigw-lambda-durable-tenant-isolation-callback-terraform

[Anandoo7]

Issue #, if available:

Description of changes:

New Serverless Pattern

Pattern name: apigw-lambda-durable-tenant-isolation-callback-terraform

Pattern description:

SaaS applications that process tenant requests often need to pause a workflow and wait for an external system to confirm before completing a payment gateway returning a charge result, a compliance system issuing a decision, or a human approver acting on a request. During this wait, the first processing step has already validated the request and cached tenant-specific data (configuration, credentials, intermediate results) in the execution environment's memory.

This pattern uses Lambda durable functions to suspend the workflow at zero compute cost and resume from a checkpoint when the external confirmation arrives. It uses Lambda tenant isolation mode to ensure the suspended execution environment including all cached in-memory state from the first step is never reassigned to another tenant during the wait period. API Gateway provides the HTTP interface for starting workflows and receiving callbacks.

Without durable execution, the function cannot suspend across the wait boundary, forcing you to externalize all state to a database and build a separate resumption mechanism. Without tenant isolation, a suspended environment's cached data could be exposed to a different tenant's invocation during the wait. Both capabilities together enable multi-tenant workflows that pause indefinitely for external input while keeping tenant state private and avoiding re-execution of completed work.

Services: Amazon API Gateway, AWS Lambda (Durable Functions + Tenant Isolation)

Framework: Terraform

Language: Node.js

Testing:

• Deployed and tested in ap-southeast-2 (Sydney)
• Verified workflow suspension, callback resumption, checkpoint replay, and per-tenant isolation across multiple concurrent tenants

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