Overview of API Gateway Trigger

You can implement backend web services by writing SCF functions and provide services through API Gateway. API Gateway passes the request content as parameters to the function and returns the result from the function back to the requester as the response.

API Gateway triggers have the following characteristics:

• Push model: After API Gateway receives an API request, if the API is configured to connect with a function on the backend of the gateway, the function will be triggered for execution, and API Gateway will encapsulate information about the API request into input parameters of the request, including the specific service and API rule that receive the request, actual path and method of the request, and request parameters such as path, header and query, and send them to the triggered function in the form of event input parameters.
• Sync call: API Gateway calls the function synchronously and waits for function return before the timeout configured in API Gateway expires. For more information about calling types, see Calling Types.

API Gateway Trigger Configuration

API Gateway triggers can be configured in the SCF console and the API Gateway console.

• In SCF console, you can add API Gateway triggers, select existing or create new API services, and define the request methods (currently, six methods are supported, i.e., "ANY", "GET", "HEAD", "POST", "PUT", and "DELETE"), environments (test, pre-release, and release environments), and authentication methods (API Gateway key pair).
• When configuring API rules in the API Gateway console, you can choose Cloud Function as the backend, and select functions in the same region as the API services. In the API Gateway console, you can configure and manage advanced API services such as traffic limiting plan, blacklist, and whitelist.

When you configure the connection with SCF in API Gateway, you also need to configure the timeout. The request timeout in API Gateway and the execution timeout in SCF take effect respectively. The timeout rules are as follows:

• API Gateway timeout > SCF timeout: The SCF timeout takes effect first, the API request response is 200 http code, but the return content is the error message of SCF timeout.
• API Gateway timeout < SCF timeout: The API Gateway timeout takes effect first, the API request response is 5xx http code, which indicates that the request timed out.

Limitation on API Gateway Trigger Binding

In API Gateway, one API rule can be bound to only one function, but one function can be bound to multiple API rules as the backend. In addition, API gateway triggers currently can only be bound to functions in the same region, for example, a function created in Guangzhou region can only be bound to and triggered by API rules created in Guangzhou region. If you want to trigger an SCF function via API Gateway configuration in a specific region, please create a function in the same region.

Request and Response

Request method is the method to process request sent from API Gateway to SCF, and response method is the method to process the returned value sent from SCF to API Gateway. Both request and response methods can be planned and implemented by means of passthrough and integration.

Integration Request and Passthrough Request

Integration request means that API Gateway converts the content of the HTTP request into request data structures which are passed to the function for handling as event input parameters of the function. The following details the request data structures.

Passthrough request means that API Gateway passes the body content of the HTTP request to the function as event input parameters of the function. The passthrough request feature is still in the planning stage. For passthrough requests, the body of the HTTP request has to be in JSON data format.

Currently, when an API Gateway trigger triggers a function, integration request is always used.

Event message structures of integration request for API Gateway trigger

When an API Gateway trigger receives a request, it sends the event data to the bound function in JSON format as shown below.

{
  "requestContext": {
    "serviceId": "service-f94sy04v",
    "path": "/test/{path}",
    "httpMethod": "POST",
    "requestId": "c6af9ac6-7b61-11e6-9a41-93e8deadbeef",
    "identity": {
      "secretId": "abdcdxxxxxxxsdfs"
    },
    "sourceIp": "10.0.2.14",
    "stage": "release"
  },
  "headers": {
    "Accept-Language": "en-US,en,cn",
    "Accept": "text/html,application/xml,application/json",
    "Host": "service-3ei3tii4-251000691.ap-guangzhou.apigateway.myqloud.com",
    "User-Agent": "User Agent String"
  },
  "body": "{\"test\":\"body\"}",
  "pathParameters": {
    "path": "value"
  },
  "queryStringParameters": {
    "foo": "bar"
  },
  "headerParameters":{
    "Refer": "10.0.2.14"
  },
  "stageVariables": {
    "stage": "release"
  },
  "path": "/test/value",
  "queryString": {
    "foo" : "bar",
    "bob" : "alice"
  },
  "httpMethod": "POST"
}

The data structures are detailed as below:

• The content of requestContext may increase during API Gateway iteration. Parameters in the data structure will be increased only but not deleted to avoid data corruption.
• Parameters in the actual request may appear in multiple locations and can be selected based on your business needs.

Integration Response and Passthrough Response

Integration response means that API Gateway parses the return content of the function and constructs an HTTP response based on the parsed content. With the aid of integration response, you can control the status code, headers, and body content of the response by using code, and implement response to content in non-JSON format, such as XML, HTML, and even JS. When using integration response, data structures need to be returned based on the rules of integration response for API Gateway trigger before they can be successfully parsed by API Gateway; otherwise, error message {"errno":403,"error":"Invalid scf response format. please check your scf response format."} will appear.

Passthrough response means that API Gateway directly passes the return content of the function to the API requester. Generally, the data format of this type of responses is fixed to JSON format, the status code is defined according to the status of function execution, and status code 200 is returned if the function is successfully executed. With passthrough response, you can obtain the JSON format and parse the structures at the call location to obtain the content in the structures.

• If the API Gateway trigger is configured through the API Gateway console, the way to handle the response is passthrough response by default. To enable integration response, select Enable integration response at the backend configuration location in the API configuration and return the content in the data structures detailed below in the code.
• If the API Gateway trigger is configured through the SCF console, the integration response feature is enabled by default. Please pay attention to the format of return data.

Return data structures of integration response for API Gateway trigger

If integration response is set for API Gateway, data structures similar to the content below need to be returned.

{
    "isBase64Encoded": False,
    "statusCode": 200,
    "headers": {"Content-Type":"text/html"},
    "body": "<html><body><h1>Heading</h1><p>Paragraph.</p></body></html>"
}

The data structures are detailed as below: