Build an API with HTTP Proxy Integration

The HTTP proxy integration of API Gateway is a simple, powerful, and versatile mechanism to build an API that allows a web application to access multiple resources or features of the integrated HTTP endpoint, for example the entire website, with a streamlined setup of a single API method. In HTTP proxy integration, API Gateway passes the client-submitted method request to the backend. The request data that is passed through includes the request headers, query string parameters, URL path variables, and payload. The backend HTTP endpoint or the web server parses the incoming request data to determine the response that it returns. In a sense, the HTTP proxy integration makes the client and backend interact directly without any intervention from API Gateway after the API method is set up.

With the all-encompassing proxy resource {proxy+}, and the catch-all ANY verb for the HTTP method, you can use an HTTP proxy integration to create an API of a single API method. The method exposes the entire set of the publicly accessible HTTP resources and operations of a website. When the backend web server opens more resources for public access, the client can use these new resources with the same API setup. To enable this, the website developer must communicate clearly to the client developer what the new resources are and what operations are applicable for each of them.

As a quick introduction, the following tutorial demonstrates the HTTP proxy integration. In the tutorial, we create an API using the API Gateway console to integrate with the PetStore website through a generic proxy resource {proxy+}, and create the HTTP method placeholder of ANY.

Topics

Create an API with HTTP Proxy Integration Using the API Gateway Console
Test an API with HTTP Proxy Integration

Create an API with HTTP Proxy Integration Using the API Gateway Console

The following procedure walks you through the steps to create and test an API with a proxy resource for an HTTP backend using the API Gateway console. The HTTP backend is the PetStore website (http://petstore-demo-endpoint.execute-api.com/petstore/pets) from Build an API with HTTP Custom Integration, in which screenshots are used as visual aids to illustrate the API Gateway UI elements. If you are new to using the API Gateway console to create an API, you may want to follow that section first.

To build an API with HTTP proxy integration with the PetStore website through a proxy resource

Sign in to the API Gateway console at https://console.aws.amazon.com/apigateway.
To create an API, choose Create new API (for creating the first API) or Create API (for creating any subsequent API). Next, do the following:
1. Choose New API.
2. Type a name in API Name.
3. Optionally, add a brief description in Description.
4. Choose Create API.
For this tutorial, use ProxyResourceForPetStore for the API name.
To create a child resource, choose a parent resource item under the Resources tree and then choose Create Resource from the Actions drop-down menu. Then, do the following in the New Child Resource pane.
1. Select the Configure as proxy resource option to create a proxy resource. Otherwise, leave it de-selected.
2. Type a name in the Resource Name* input text field.
3. Type a new name or use the default name in the Resource Path* input text field.
4. Choose Create Resource.
5. Select Enable API Gateway CORS, if required.
For this tutorial, select Configure as proxy resource. For Resource Name, use the default, proxy. For Resource Path, use /{proxy+}. Select Enable API Gateway CORS.
To set up the ANY method for integration with the HTTP backend, do the following:
1. Choose the resource just created and then choose Create Method from the Actions drop-down menu.
2. Choose ANY from the HTTP method drop-down list and then choose the check mark icon to save the choice.
3. Choose HTTP Proxy for Integration type.
4. Type an HTTP backend resource URL in Endpoint URL.
5. Use default settings for other fields.
6. Choose Save to finish configuring the ANY method.
For this tutorial, use http://petstore-demo-endpoint.execute-api.com/{proxy} for the Endpoint URL.

In the API just created, the API's proxy resource path of {proxy+} becomes the placeholder of any of the backend endpoints under http://petstore-demo-endpoint.execute-api.com/. For example, it can be petstore, petstore/pets, and petstore/pets/{petId}. The ANY method serves as a placeholder for any of the supported HTTP verbs at run time.

Test an API with HTTP Proxy Integration

Whether a particular client request succeeds depends on the following:

If the backend has made the corresponding backend endpoint available and, if so, has granted the required access permissions.
If the client supplies the correct input.

For example, the PetStore API used here does not expose the /petstore resource. As such, you get a 404 Resource Not Found response containing the error message of Cannot GET /petstore.

In addition, the client must be able to handle the output format of the backend in order to parse the result correctly. API Gateway does not mediate to facilitate interactions between the client and backend.

To test an API integrated with the PetStore website using HTTP proxy integration through the proxy resource

To use the API Gateway console to test invoking the API, do the following.
1. Choose ANY on a proxy resource in the Resources tree.
2. Choose Test in the Method Execution pane.
3. From the Method drop-down list, choose an HTTP verb supported by the backend.
4. Under Path, type a specific path for the proxy resource supporting the chosen operation.
5. If required, type a supported query expression for the chosen operation under the Query Strings heading.
6. If required, type one or more supported header expressions for the chosen operation under the Headers heading.
7. If configured, set the required stage variable values for the chosen operation under the Stage Variables heading.
8. If prompted and required, choose an API Gateway-generated client certificate under the Client Certificate heading to the operation to be authenticated by the back end.
9. If prompted, type an appropriate request body in the text editor under the Request Body heading.
10. Choose Test to test invoking the method.
For this tutorial, use GET for Method in place of ANY, use petstore/pets for Path in place of the proxy resource path ({proxy}), and type=fish for Query Strings.

Because the backend website supports the GET /petstore/pets?type=fish request, it returns a successful response similar to the following:
```
[
  {
    "id": 1,
    "type": "fish",
    "price": 249.99
  },
  {
    "id": 2,
    "type": "fish",
    "price": 124.99
  },
  {
    "id": 3,
    "type": "fish",
    "price": 0.99
  }
]
```
If you try to call GET /petstore, you get a 404 response with an error message of Cannot GET /petstore. This is because the backend does not support the specified operation. If you call GET /petstore/pets/1, you get a 200 OK response with the following payload, because the request is supported by the PetStore website.
```
{
  "id": 1,
  "type": "dog",
  "price": 249.99
}
```
To use a browser to call a GET method on a specific resource of the API, do the following.
1. If you have not done so, choose Deploy API from the Actions drop-down menu for the API you created. Follow the instructions to deploy the API to a specific stage. Note the Invoke URL that displays on the resulting Stage Editor page. This is the base URL of the API.
2. To submit a GET request on a specific resource, append the resource path, including possible query string expressions to the Invoke URL value obtained in the previous step, copy the complete URL into the address bar of a browser, and choose Enter.
For this tutorial, deploy the API to a test stage and append petstore/pets?type=fish to the API's Invoke URL. This produces a URL of https://4z9giyi2c1.execute-api.us-west-2.amazonaws.com/test/petstore/pets?type=fish.

The result should be the same as returned when you use TestInvoke from the API Gateway console.

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