API Gateway allows developers to override HTTP status codes returned by backend integrations, providing greater control over API responses. This feature is particularly useful when you need to transform backend responses into more meaningful HTTP status codes for your API consumers.
By default, AP…API Gateway allows developers to override HTTP status codes returned by backend integrations, providing greater control over API responses. This feature is particularly useful when you need to transform backend responses into more meaningful HTTP status codes for your API consumers.
By default, API Gateway passes through the status code received from your backend integration. However, there are scenarios where you might want to modify this behavior. For example, your Lambda function might return a 200 status code with an error message in the body, but you want to return a 400 or 500 status code to the client.
To override status codes, you configure Integration Responses in API Gateway. Here's how it works:
1. **Method Response Configuration**: First, define all possible HTTP status codes your API method can return (200, 400, 404, 500, etc.).
2. **Integration Response Mapping**: Create integration response mappings that match specific patterns in your backend response. You can use regex patterns to match error messages or specific response content.
3. **Selection Pattern**: Use selection patterns to identify which responses should trigger a status code override. For Lambda integrations, you can match against the errorMessage field or custom error patterns.
4. **Response Templates**: Apply mapping templates to transform the response body while also changing the status code.
For Lambda Proxy Integration, the Lambda function itself controls the status code by returning a response object with a statusCode property. For non-proxy integrations, you rely on Integration Response configurations.
Common use cases include:
- Converting Lambda errors to appropriate 4xx or 5xx codes
- Standardizing responses from legacy backends
- Implementing custom error handling strategies
- Mapping backend-specific codes to RESTful conventions
This capability ensures your API presents a consistent, well-designed interface to consumers regardless of how your backend services structure their responses.
Overriding API Status Codes in AWS API Gateway
What is Overriding API Status Codes?
Overriding API status codes is a feature in AWS API Gateway that allows you to modify the HTTP status code returned to the client, regardless of what your backend integration returns. This is particularly useful when you need to transform responses from Lambda functions, HTTP endpoints, or other AWS services to return appropriate status codes to your API consumers.
Why is it Important?
1. RESTful Compliance: Ensures your API follows REST conventions by returning proper status codes (201 for created resources, 404 for not found, etc.)
2. Backend Abstraction: Allows you to hide backend implementation details and present a consistent API interface
4. Client Experience: Provides meaningful status codes that client applications can properly handle
How It Works
In API Gateway, you override status codes using Integration Responses and Method Responses:
1. Method Response: Define which HTTP status codes your API method can return (200, 400, 404, 500, etc.)
2. Integration Response: Map backend responses to specific status codes using regex patterns
3. Selection Pattern: Use regular expressions to match error messages or response patterns from your backend
For example, if your Lambda function throws an error with message containing NotFound, you can configure a selection pattern .*NotFound.* to return a 404 status code.
Configuration Steps:
- Create Method Response entries for each status code you want to return - Configure Integration Response mappings with selection patterns - The default integration response (empty selection pattern) handles successful responses - Error patterns are evaluated in order, with the first match being used
Lambda Proxy Integration vs Custom Integration:
With Lambda Proxy Integration, the Lambda function controls the status code by including it in the response object. With Custom Integration, API Gateway uses integration response mappings to determine the status code.
Exam Tips: Answering Questions on Overriding API Status Codes
1. Know the difference between Method Response and Integration Response: Method Response defines what status codes are possible; Integration Response defines the mapping logic
2. Understand regex selection patterns: Questions may test your knowledge of how patterns like .*Error.* match backend responses
3. Lambda Proxy vs Custom Integration: Remember that Lambda Proxy integration returns the status code from the Lambda function itself, while custom integration requires mapping configuration
4. Default response: The integration response with an empty selection pattern is the default and typically maps to 200 OK
5. Error handling scenarios: Expect questions about mapping specific error types to appropriate 4xx or 5xx status codes
6. Order matters: Selection patterns are evaluated in order; more specific patterns should come before generic ones
7. Common use case: When you see questions about returning proper REST status codes from Lambda functions through API Gateway, think about integration response mappings
8. Mapping templates: Know that you can also transform response bodies alongside status code overrides using mapping templates