Request/Response Transformation in AWS API Gateway

1. Introduction

AWS API Gateway provides a powerful way to create, publish, maintain, monitor, and secure APIs at any scale. One of its core features is Request/Response Transformation, which allows you to modify both incoming requests and outgoing responses according to your needs.

2. Key Concepts

**Request Transformation**: Modifying the incoming requests before passing them to the backend service.
**Response Transformation**: Modifying the responses received from the backend before sending them to the client.
**Mapping Templates**: Templates written in Velocity Template Language (VTL) that define how to transform requests and responses.
**Content-Type**: The format of the data being sent (e.g., JSON, XML). Transformation can be based on content-type.

3. Step-by-Step Process

3.1 Creating a Mapping Template

Mapping templates are used for both request and response transformations. Below are steps to create a mapping template in API Gateway.

Note: Ensure that the content-type of the request and response is set correctly to use the appropriate mapping template.

Step 1: Open API Gateway

Step 2: Select Your API

Step 3: Choose the Resource and Method

Step 4: Select Integration Request or Integration Response

Step 5: Add Mapping Template


{
    "name": "$input.path('$.name')",
    "age": "$input.path('$.age')",
    "requestId": "$context.requestId"
}

3.2 Testing the Transformation

After creating the mapping template, you can test it using the API Gateway console or Postman.

4. Best Practices

Use VTL syntax correctly to avoid transformation errors.
Test your templates with various payloads to ensure they work as expected.
Keep the transformations simple and maintainable.
Document your mapping templates for future reference.

5. FAQ

What is Velocity Template Language (VTL)?

VTL is a templating language used by AWS API Gateway for request and response transformation. It allows you to extract and manipulate data from incoming requests and format outgoing responses.

Can I use multiple mapping templates?

Yes, you can define multiple mapping templates for different content types (e.g., application/json, application/xml) and different methods.

Where can I view the execution logs for transformations?

You can enable logging in API Gateway to view execution logs that include transformation details. This can be done under the Stage settings.

6. Flowchart of Request/Response Transformation


graph TD;
    A[Start] --> B[Receive Request];
    B --> C{Transform Request?};
    C -->|Yes| D[Apply Mapping Template];
    C -->|No| E[Forward to Backend];
    D --> E;
    E --> F[Receive Response];
    F --> G{Transform Response?};
    G -->|Yes| H[Apply Mapping Template];
    G -->|No| I[Send Response to Client];
    H --> I;
    I --> J[End];