Mocking API responses in Azure API Management

Ilias el Matani

Introduction

In today's API-driven software architecture, developers often face a unique challenge: designing the API façade ahead of its backend implementation. This blog delves into this predicament and offers a practical solution to maintain momentum in such situations.

The challenge

In many software projects, there's a phase where the API façade is ready, but the backend service fulfilling its contract is still under construction. When using Azure API Management Service in such a context, a challenge emerges: without a backend, APIM consistently produces 500 HTTP errors. This can disrupt frontend or client-side development that relies on any form of API responses, even if they're just mock data.

The solution

Azure API Management offers a mocking response feature, precisely for situations like these. When you design an API, but the backend isn't ready, you can set up mock responses for your operations. This ensures that any consumer of the API receives a consistent, pre-defined response, aiding in parallel development and testing.

Crafting a placeholder API

We will create a simple HTTP API that doesn’t need a pre-existing backend.

  • Start by signing into the Azure portal and then making your way to your specific API Management instance.
  • Opt for APIs, followed by + Add API and then HTTP tile.

Define the blueprint of the API

  • Upon the appearance of the "Create an HTTP API" panel, select the Full option.
  • Designate the "Display name" as Test API.
  • For the "Products", opt for Unlimited.
  • Ensure that the Managed option is chosen under "Gateways".
  • Finalize by clicking on Create.

Enriching the API with an operation

Every API exposes operations. Here, we'll add one to our HTTP API.

  • First, select the previously created API.
  • Click on + Add Operation.
  • In the dedicated "Frontend" panel, provide:
  • "Display name": Test call.
  • "URL (HTTP verb)": GET.
  • "URL": /test.
  • Optionally, add a brief "Description" for clarity.
  • Jump to the Responses tab to outline response status codes, content types, and more.
  • Click + Add response and choose 200 OK.
  • Under the "Representations" banner, select + Add representation and opt for the application/json content type.
  • In the "Sample" field, jot down { "sampleField" : "sampleValue" }.
  • Save these configurations.

Activating mock responses

Azure API Management's mock response feature truly shines here:

  • Revisit the API you crafted in step one.
  • On the right-hand side panel, activate the Design tab.
  • Highlight the test operation you appended earlier.
  • Within the "Inbound processing" section, go for + Add policy.
  • In the ensuing gallery, click on Mock responses.
  • In the dedicated textbox, spell out 200 OK, application/json. This is an indication for the API to return the mock response we established earlier.
  • Hit Save.

Note: Post this, a yellow alert displaying "Mocking is enabled" should surface. This confirms that the API Management responses are not sourced from the backend but are mock-generated.

Validating the mock API

  • Go back to the initial API.
  • Engage the Test tab.
  • Ensure Test call API is active, and then hit Send to initiate a test call.
  • If all goes as planned, the HTTP response should mirror the JSON blueprint established earlier.

Conclusion

Azure API Management's mock response capability is a pivotal tool, especially for those inevitable moments when the backend isn't immediately available. With this blog, I hope that you're equipped to maintain seamless development and testing phases, ensuring no disruptions even in the absence of a functional backend.