Oracle® Fusion Middleware
Part 24. Routing Filters

This topic describes how to configure the API Gateway to send messages to external Web services. The API Gateway offers a number of different filters that can be used to route messages. Depending on how the API Gateway is perceived by the client, different combinations of routing filters can be used.

For example, the API Gateway can act both as a proxy and as an endpoint (in-line) server for a client, depending on how the client is configured. In each case, the request received by the API Gateway appears slightly different, and the API Gateway can take advantage of this when routing the message onwards. Furthermore, the API Gateway can provide service virtualization by shielding the underlying hierarchy of back-end Web services from clients.

This topic explains how clients can use the API Gateway both as a proxy and as an endpoint server. It then shows how service virtualization works. When these basic concepts are explained, this topic helps you to identify the combination of routing filters that is best suited to your deployment scenario.

The API Gateway can be used by clients as both a proxy server and an endpoint server. When a client uses the API Gateway as a proxy server, it sends up the complete URL of the destination Web service in the HTTP request line. The API Gateway can use the URL to determine the host and port to route the message to. The following example shows an HTTP request received by the API Gateway when acting as a proxy for a client:

POST http://localhost:8080/services/getHello HTTP/1.1

Alternatively, when the API Gateway is acting as an endpoint (in-line) server, the client sends the request directly to the API Gateway. In this case, the request line appears as follows:

POST /services/getHello HTTP/1.1

In this case, only the path on the server is specified, and no scheme, host, or port number is included in the HTTP request line. Because this information is not provided by the client, the API Gateway must be explicitly configured to route the message on to the specific destination.

It is sometimes desirable to shield the underlying structure of the directory hierarchy in which Web services reside from external clients. You can do this by providing a mapping between the path that the client accesses and the actual path at which the Web service resides.

For example, suppose you have two Web services accessible at the /helloService/getHello and /financeService/getQuote URIs. You may wish to hide that these services are deployed under different paths, perhaps exposing them under a common /services base URI (for example, /services/getHello and /services/getQuote). The client is therefore unaware of the underlying hierarchy (for example, directory structure) of the two Web services. This is termed service virtualization.

This section first identifies how your clients perceive the API Gateway, and then determines whether you wish to virtualize your back-end Web services. Depending on these requirements, you can use different combinations of routing filters, as described in the use cases in the subsequent sections.

Consider the following to determine which combination of routing filters is most appropriate for your scenario:

Proxy or Endpoint?

Service Virtualization?

These permutations are summarized in the following table:

In this case, the API Gateway is configured as an HTTP proxy for the client, and maintains the original path used by the client in the HTTP request. For example, if the API Gateway is listening at http://localhost:8080/, and the Web service is running at http://localhost:5050/services/getQuote, the request line of the client HTTP request appears as follows:

POST http://localhost:5050/services/getQuote HTTP/1.1

Because the client is configured to use the API Gateway instance running on localhost at port 8080 as its HTTP proxy, the client automatically sends all messages to the proxy. However, it includes the full URL of the ultimate destination of the message in the request line of the HTTP request.

When the API Gateway receives the request, it extracts this URL from the request line and uses it to determine the destination of the message. In the above example, the API Gateway routes the message on to http://localhost:5050/services/getQuote.

You can configure the following policy to route the message to the URL specified in the request line of the client request:

The following table explains the role of each filter in the policy. For more information on a specific filter, click the appropriate link in the Details column.

In this case, the API Gateway is also perceived as an HTTP proxy by the client. However, the API Gateway exposes a virtualized view of the services that it protects. This is termed service virtualization.

To achieve this, the API Gateway must provide a mapping between the path used by the client and the path under which the service is deployed. Assuming the API Gateway is running at http://localhost:8080/services, and the Web service is deployed at http://localhost:5050/financialServices/quotes/getQuote, the following example shows what the client may send up in the HTTP request line:

POST http://localhost:5050/services/getQuote HTTP/1.1

To achieve this, the API Gateway must provide a mapping between what the client requests (/services/getQuote), and the address of the Web service (/financialServices/quotes/getQuote. The Rewrite URL filter in the following policy fulfills this role:

The following table explains the roles of the each filter in the policy:

In this scenario, the client sees the API Gateway as the endpoint to its connection, and the API Gateway must be configured to route messages on to a specific destination. For example, assuming that the API Gateway is running at http://localhost:8080/services, the request line of the client's HTTP request is received by the API Gateway as follows:

POST /services HTTP/1.1

The request line above shows that no information about the scheme, host, or port of the destination Web service is specified. Therefore, this information must be configured in the API Gateway so that it knows where to route the message on to. The Static Router enables the user to enter connection details for the destination Web service.

Assuming that the Web service is running at http://localhost:5050/stockquote/getPrice, the host, port, and scheme respectively are: localhost, 5050, and http. You must explicitly configure this information in the Static Router. The following policy illustrates this scenario:

The following table explains the role of each filter in the above policy:

In this case, the API Gateway acts as the endpoint to the client connection (and not as a proxy), and hides the deployment hierarchy of protected Web services from clients (performs service virtualization).

In this scenario, the client sends messages directly to the API Gateway. For example, assuming that the API Gateway is running at http://localhost:8080/services, and the Web service is running at http://localhost:5050/stockquote/getPrice, the request line of the client HTTP request is received by the API Gateway as follows:

POST /services HTTP/1.1

You can then configure the Static Router filter to route the message on to port 8080 on localhost using the http scheme, while the Rewrite URL filter provides the mapping between the path requested by the client (/services) and the path under which the Web service is deployed (/stockquote/getPrice). The following policy illustrates a sample policy that provides service virtualization when the API Gateway is used as an endpoint:

The following table explains the role of each filter in the policy:

In some cases, the API Gateway must route the incoming message to an entirely different URL. You can use the Rewrite URL filter for this purpose, in addition to rewriting the path on which the request is received (as described in cases 2 and 4 above).

The following policy illustrates the use of the Redirect URL filter to route messages to a fully qualified URL:

The following table describes the role of each filter in the policy:

This is a more advanced case where the API Gateway is configured to route on through an HTTP proxy to the back-end Web service sitting behind the proxy. When the API Gateway is configured to route through a proxy, it connects directly to the proxy, and sends a request including the full URL of the target Web service in the HTTP request URI. When the HTTP proxy receives this request, it uses the URL in the request line to determine where to route the message to. The following example shows the request line of a request made through a proxy:

POST http://localhost:8080/services/getQuote HTTP/1.1

The following filters are required to configure the API Gateway to route through an HTTP proxy:

The following are the key concepts to consider when configuring the API Gateway to connect to external Web services: