Adding a Gateway Response

Scenario

A gateway response is displayed if APIG fails to process an API request. APIG provides a set of default responses and also allows you to create gateway responses with custom status codes and content, on the API Groups page. The response content must be in JSON format.

For example, the content of a default gateway response is as follows:

{"error_code": "$context.error.code", "error_msg": "$context.error.message", "request_id": "$context.requestId"}

You can add a response with the following content:

{"errorcode": "$context.error.code", "errormsg": "$context.error.message", "requestid": "$context.requestId","apiId":"$context.apiId"}

You can add more fields to or delete existing fields from the JSON body.

The default gateway responses provided by APIG can be edited.
You can create gateway responses and configure different responses for APIs in the same API group.
The type of a gateway response cannot be changed. For details, see Response Types.
Gateway responses can contain the API gateway context variables (starting with $context). For details, see APIG Context Variables.

Prerequisites

You have created an API group.

Procedure

Access the shared gateway console.
In the navigation pane, choose API Publishing > API Groups.
Locate the API group for which you want to create or modify a gateway response, and click the group name to go to the API group details page.
Click the Gateway Responses tab and create a gateway response.
- To edit a response, click the Edit button in the upper right corner and modify the status code and content of the response.
- You can modify only the status code and content of a default or custom gateway response, and you cannot change the response type.
- Error information and other response details can be obtained using variables. For details about the supported variables, see Table 2.

Response Types

Table 1 lists the response types supported by APIG. You can define status codes of responses to meet your service requirements.

**Table 1** Error Response types supported by APIG
Response Name	Default Status Code	Description
Access Denied	403	Access denied. For example, the access control policy is triggered or an attack is detected.
Authorizer Configuration Error	500	A custom authorizer error has occurred. For example, communication failed or an error response was returned.
Authorizer Failed	500	The custom authorization failed.
Incorrect Identity Source	401	The identity source of the custom authorizer is missing or invalid.
Authentication Failure	401	IAM or app authentication failed.
Identity Source Not Found	401	No identity source has been specified.
Backend Timeout	504	Communication with the backend service timed out.
Backend Unavailable	502	The backend service is unavailable due to communication error.
Default 4XX	-	Another 4XX error occurred.
Default 5XX	-	Another 5XX error occurred.
No API Found	404	No API is found.
Incorrect Request Parameters	400	The request parameters are incorrect or the HTTP method is not supported.
Request Throttled	429	The request was rejected due to request throttling.
Unauthorized App	401	The app you are using has not been authorized to call the API.

APIG Context Variables

**Table 2** Variables that can be used in response message body
Variable	Description
$context.apiId	API ID.
$context.appId	ID of the app that calls the API.
$context.requestId	Request ID generated when the API is called.
$context.stage	Deployment environment in which the API is called.
$context.sourceIp	Source IP address of the API caller.
$context.authorizer.frontend.property	Values of the specified attribute–value pairs mapped to the context in the frontend custom authorizer response
$context.authorizer.backend.property	Values of the specified attribute–value pairs mapped to the context in the backend custom authorizer response
$context.error.message	Error message.
$context.error.code	Error code.
$context.error.type	Error type.