Routing Configuration

Contents

Overview

The purpose of this guide is to describe how to configure the Enterprise Gateway to send messages to external Web Services. The Enterprise Gateway offers a number of different filters that can be used to route messages. Depending on how the Enterprise Gateway is perceived by the client, different combinations of routing filters can be used.

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

In the next section, we will explain how clients can use the Enterprise Gateway as both a proxy and as an endpoint server. We will then go on to show how service virtualization works. Once these basic concepts have been explained, we will help you to identify the combination of routing filters that is best suited to your deployment scenario.

Proxy or Endpoint Server

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

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

Alternatively, when the Enterprise Gateway is acting as an endpoint (i.e. in-line) server, the client sends the request directly to the Enterprise 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. Since this information is not provided by the client, the Enterprise Gateway must be explicitly configured to route the message on to the specific destination.

Service Virtualization

It is sometimes desirable to shield the underlying structure of the directory hierarchy in which Web Services reside from external clients. This can be done by providing a mapping between the path that the client accesses and the actual path at which the Web Service resides.

For example, suppose we have 2 Web Services accessible at the URIs, /helloService/getHello and /financeService/getQuote. We may want to hide the fact that these services are actually 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 (e.g. directory structure) of the 2 Web Services. This is called service virtualization.

Choosing the Correct Routing Filters

The purpose of this section is to identify, first, how your clients perceive the Enterprise Gateway, and second, to determine whether or not you wish to virtualize your back-end Web Services. Depending on these requirements, different combinations of routing filters can be used, as outlined in the 4 "cases" described in the subsequent sections.

In order to determine the combination of routing filters that is most appropriate for your scenario, it is necessary to consider your answers to the following simple questions:

Proxy or Endpoint

  • Is the client using the Enterprise Gateway as a proxy? If so, then you will be interested in cases 1 or 2 below, depending on whether service virtualization is required or not.
  • Alternatively, is the client using the Enterprise Gateway as the endpoint of the connection, i.e. as an in-line server? If so, then you should look at cases 3 or 4 below.

Service Virtualization

  • Do you want to shield the actual hierarchy of protected Web Services by exposing a virtual view of these services? If so, then cases 2, 4, and 5 below will be of interest.
  • Is service virtualization important? If not, then you should refer to cases 1 and 3 below.

The above permutations can be summarized in the following table:

Proxy or Endpoint Service Virtualization Example
Proxy No Case 1: Proxy without Virtualization
Proxy Yes Case 2: Proxy with Virtualization
Endpoint No Case 3: Endpoint without Virtualization
Endpoint Yes Case 4: Endpoint with Virtualization
Proxy or Endpoint Yes Case 5: Simple Redirect

Case 1: Proxy without Service Virtualization

In this case, the Enterprise Gateway is configured as an HTTP proxy for the client and will maintain the original path used by the client in the HTTP request. So for example, if the Enterprise Gateway is listening at http://localhost:8080/, and the Web Service is running at http://localhost:5050/services/getQuote, then the request line of the client HTTP request will appear as follows: 

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

Since the client has been configured to use the Enterprise Gateway instance running on localhost at port 8080 as its HTTP proxy, the client will automatically send all messages to the proxy. However, it will include the full URL of the ultimate destination of the message in the request line of the HTTP request.

When the Enterprise 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 Enterprise Gateway will route the message onwards to http://localhost:5050/services/getQuote.

The following policy can be configured to route the message to the URL specified in the request line of the client request:

Policy 1: Proxy without Service Virtualization

Policy 1: Proxy without Service Virtualization

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

Filter Role in Policy Help
Dynamic Router Extracts the URL of the destination Web Service from the request line of the incoming HTTP request. The Dynamic Router is usually used when the Enterprise Gateway is perceived as a proxy by the client. Dynamic Router
Connection Responsible for establishing the connection to the destination Web Service and sending the message over this connection. This connection can be mutually authenticated if necessary. Connection

Case 2: Proxy with Service Virtualization

In the second case, the Enterprise Gateway is also perceived as an HTTP proxy by the client. However, this time the Enterprise Gateway exposes a virtualized view of the services that it protects, i.e. service virtualization.

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

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

To achieve this, the Enterprise Gateway must provide a mapping between what the client requests, i.e. /services/getQuote, and the actual address of the Web Service, i.e. /financialServices/quotes/getQuote. The Rewrite URL filter in the following policy fulfills this role:

Policy 2: Proxy with Service Virtualization

Policy 2: Proxy with Service Virtualization

The following table explains the roles of the 3 filters within the policy:

Filter Role in Policy Help
Dynamic Router Extracts the URL of the destination Web Service from the request line of the incoming HTTP request. The Dynamic Router is usually used when the Enterprise Gateway is perceived as a proxy by the client. Dynamic Router
Rewrite URL Specifies the mapping between the path requested by the client and the actual path under which the Web Service is deployed, therefore providing service virtualization. Rewrite URL
Connection Responsible for establishing the connection to the destination Web Service and sending the message over this connection. This connection can be mutually authenticated if necessary. Connection

Case 3: Endpoint without Service Virtualization

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

POST /services HTTP/1.1

It is clear from the request line above that no information about the scheme, host, or port of the destination Web Service is specified. Therefore, this information must be configured in the Enterprise Gateway so that it knows where to route the message on to. The Static Router allows 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 as follows: "localhost", "5050", and "http". This information must be explicitly configured in the Static Router. The following policy illustrates this scenario:

Policy 3: Endpoint without Service Virtualization

Policy 3: Endpoint without Service Virtualization

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

Filter Role in Policy Help
Static Router Allows the user to explicitly specify the host, port, and scheme at which the Web Service is listening. This filter must be used when the client sees the Enterprise Gateway as the endpoint to its connection, i.e. the Enterprise Gateway is not acting as a proxy for the client. Static Router
Connection Responsible for establishing the connection to the destination Web Service and sending the message over this connection. This connection can be mutually authenticated if necessary. Connection

Case 4: Endpoint with Service Virtualization

In the last case, the Enterprise Gateway is acting as the endpoint to the client connection (i.e. it is not acting as a proxy) and is hiding the deployment hierarchy of protected Web Services from clients. In other words, it is performing service virtualization.

In this scenario, the client will send messages directly to the Enterprise Gateway. So, for example, assuming that the Enterprise 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's HTTP request will be received by the Enterprise Gateway as follows: 

POST /services HTTP/1.1

The Static Router must then be configured 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 (i.e. /services and the path under which the Web Service is deployed (i.e. /stockquote/getPrice). The following policy illustrates a sample policy that will provide service virtualization when the Enterprise Gateway is used as an endpoint:

Policy 4: Endpoint with Service Virtualization

Policy 4: Endpoint with Service Virtualization

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

Filter Role in Policy Help
Static Router Allows the user to explicitly specify the host, port, and scheme at which the Web Service is listening. This filter must be used when the client sees the Enterprise Gateway as the endpoint to its connection, i.e. the Enterprise Gateway is not acting as a proxy for the client. Static Router
Rewrite URL Provides the mapping between the path requested by the client and the path under which the Web Service is deployed. Rewrite URL
Connection Responsible for establishing the connection to the destination Web Service and sending the message over this connection. This connection can be mutually authenticated if necessary. Connection

Case 5: Simple Redirect

In some cases, it is necessary for the Enterprise Gateway to simply route the incoming message to an entirely different URL. The Rewrite URL filter can be used for this purpose, in addition to simple rewriting the path on which the request was received as described in cases 2 and 4 above. Note that the full URL of the destination Web Service should be specified in this case in the Rewrite URL filter.

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

Policy 5: Simple Redirect

Policy 5: Simple Redirect

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

Filter Role in Policy Help
Rewrite URL Used to specify the fully qualified URL of the destination Web Service. Rewrite URL
Dynamic Router In this case, the Dynamic Router is used to parse the URL specified in the Rewrite URL filter into its constituent parts. The HTTP scheme, port, and host of the Web Service are extracted and set to the internal message object for use by the Connection filter. Dynamic Router
Connection Responsible for establishing the connection to the destination Web Service and sending the message over this connection. This connection can be mutually authenticated if necessary. Connection

Case 6: Routing via an HTTP Proxy

The Enterprise Gateway can be configured to route through an HTTP proxy in cases where the back-end Web Service sits behind a proxy. When the Enterprise 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 on 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 Enterprise Gateway to route through an HTTP proxy:

Filter Role in Policy Help
Static Router You must explicitly specify the host, port, and scheme of the HTTP proxy in this filter. Static Router
Rewrite URL Enter the full URL of the Web Service in this filter, for example, http://HOST:8080/myServices. Because we are routing through a proxy, the full URL specified here will be sent in the request line of the HTTP request. Rewrite URL
Connection In this case, the Connection filter connects to the HTTP proxy, which in turn routes the message on to the destination server named in the request URI. The Send via Proxy switch must be enabled on the Connection filter to facilitate this. Connection

It is important to note the differences between how the filters are configured to route through a proxy and the situation described in case 4 above where no proxy is involved.

  • Static Router Filter:
    When the Enterprise Gateway is to route via an HTTP proxy, the Static Router is configured with the details of the HTTP proxy. Otherwise, the Static Router is given the details of the Web Service endpoint directly.
  • Rewrite URL Filter:
    The full URL of the Web Service endpoint must be specified in this filter when the Enterprise Gateway routes through a proxy. The full URL is then included in the request line of the HTTP request to the proxy. In cases where no proxy is involved, the Rewrite URL is only necessary when the back-end Web Services are virtualized. In this case, the Enterprise Gateway must send the request to a different URI than that requested by the client.
  • Connection Filter:
    When routing through a proxy, the Send via Proxy switch must be enabled on the Connection filter. This is not necessary when no proxy sits between the Enterprise Gateway and the back-end Web Service.

Summary

The following points illustrate the key concepts to consider when configuring the Enterprise Gateway to connect to external Web Services:

  • The Connection filter must always be used since it is responsible for establishing the connection to the Web Service.
  • Service virtualization can be achieved using the Rewrite URL filter.
  • If the client is configured to use the Enterprise Gateway as a proxy, the Enterprise Gateway can use the Dynamic Router to extract the URL from the request line of the HTTP request. It can then route the message on to this URL.
  • If the client sees the Enterprise Gateway as the endpoint of the connection (i.e. not as a proxy), then the Static Router must be used to explicitly configure the host, port, and scheme of the destination Web Service.