Abstract
This chapter shows how to configure multiple proxy servers to improve caching and fault tolerance on your network. You’ll get a good look at distributed content caching, including proxy chaining and proxy server arrays.
HIERARCHICAL CONFIGURATIONS
If you have multiple proxy servers on your network, you can configure a proxy server chain to distribute the Web cache. Microsoft Proxy Server 2.0 can form hierarchical configurations with Proxy Server 1.0 and other third-party proxy servers. Proxy server chains are well suited for networks with geographically separated segments, such as branch offices. The proxy chain allows servers to query an upstream server’s cache before calling the Internet (Figure 1).
Note: Proxy chaining is also known as proxy cascading and hierarchical caching.
This type of configuration allows the clients in the branch office to benefit from a local cache and the cache at the main office. The main office cache is checked before the Internet is queried. In addition, the main office proxy can be configured to call the Internet to get the information.
Tip: Proxy chaining improves cache performance and balances the caching load by placing information closer to proxy clients.
Proxy Server Routes
You can configure proxy server chains through the Routing tab on the Web Proxy Service dialog box. Only client requests for the Web Proxy service can be routed upstream because only the Web Proxy service uses caching.
Tip: WinSock and Socks Proxy Services do not support caching, chaining, or upstream routing.
To configure upstream routing, follow these steps:
Open the Internet Service Manager.
Double-click the Web Proxy service icon.
Click the Routing tab. By default, the Routing tab is configured only with the name of your proxy server and the Use Direction Connection radio button is selected. However, in Figure 2, the options have been modified as an example.
Ensure that the correct local server computer name appears in the “Use this Http Via Header alias for the local server.”
In the Upstream Routing section choose one of the following:
“Use direct connection” to route all Web Proxy client requests that aren’t resolved by the local Web cache to the Internet.
“Use Web Proxy or array” to route all Web Proxy client requests that aren’t resolved by the local Web cache upstream to another Proxy Server computer or array.
If you’re routing to an upstream Web Proxy or array, click the Modify button to configure the Advanced Routing Options dialog box (Figure 3). In this dialog box, you can configure the name of the upstream proxy server or array and the TCP port on which to contact it (usually 80). As the proxy server or array name is entered, the Array URL text box will be filled in automatically. When the “Auto-poll upstream proxy for array configuration” checkbox is checked, the local proxy server queries the proxy array to get the latest routing and status information from the array before routing requests. There is also a place to enter user credentials in order to communicate with the upstream proxy server or array. This is only necessary if the WWW service on the upstream server doesn’t allow anonymous logon. You can configure a username, password, and the type of authentication you would like. Once you’re finished configuring this dialog box, click OK to implement your changes.
If you would like to configure a backup route, in case the upstream proxy server or array isn’t available, click the “Enable backup route” checkbox. Then configure the options (Figure 2), which are identical to those explained in steps 5 and 6 — the only difference is that you are configuring a backup route.
Click OK to confirm your changes.
Tip: When you enable a backup route, you configure a level of fault-tolerance in your routing configuration.
Notice that there is a “Routing within array” section on the Routing tab of the Web Proxy Service Properties dialog box (Figure 2). This option is discussed in the proxy array section later in this chapter.
Tip: To optimize routing, direct your primary upstream route to the fastest connection to the external network.
ARRAYS
Microsoft Proxy Server 2.0 can only form an array with other Microsoft Proxy Server 2.0 systems. An array is a peer-to-peer configuration of proxy servers instead of a hierarchy as described in the first section of this chapter. The proxy array offers efficient caching, load balancing, and fault-tolerance for proxy servers. Figure 4 illustrates how a proxy array might be integrated into a network.
In the figure, both clients and other proxy servers can use the array. Each of the array members copy configuration information to the other. Table 1 lists the information that is replicated between array members and the information that is not.
Tip: Configuring an array provides fault-tolerance because if one array member fails, the others continue to function in place of the failed member.
Because configuration information is synchronized between the members of a proxy array, it is wise not to have two different administrators configuring the array at any given time. If by chance two administrators do configure the array simultaneously, synchronization errors may occur.
Configuring Arrays
If you have two or more proxy servers on your network, you can combine them into an array. You can either create or join an array via the Array dialog box. To create or join an array, follow these steps:
Open the Internet Service Manager.
Double-click any of the proxy server service icons.
Click the Array button on the Service tab of the Proxy Service Properties dialog box.
Click the Join Array button.
In the Join Array dialog box, enter the name of a proxy server computer that you would like to join in an array. If the proxy server you name isn’t already part of an array, you will see the New Array dialog box (Figure 5). If this is the case, configure a name for the proxy array, then click OK.
Click OK to confirm the proxy array settings.
When you create a new array, the computer you’re using to create the array copies its configuration to the computer you’re joining. If you join an existing array, your current configuration is copied from the existing array. This only occurs when the “Synchronize configuration of array members” checkbox is selected. If you join an unsynchronized array, a warning message is displayed and you must manually configure the array members.
Monitoring the Array
Only administrators have the ability to configure, view, and modify the proxy server array. Administrators can view the configuration of the proxy array through the Array dialog box, available through the Proxy Service Property dialog box of any proxy server service (Figure 6). Each proxy server array member keeps a current list of the array members and the status of each member. The array status information is also available to downstream proxy servers and client computers.
An administrator can also view the array membership table and verify the status of any array member with a Web browser. Figure 7 illustrates the format and result of the request for obtaining information on the Proxy array membership and status.
Tip: In order to obtain array status and membership information, connect to the Web address http://proxyserver/array.dll?Get.Info.v1, where proxyserver is the actual name of a Proxy Server array member.
Technical note: By default, execute access is disabled on the root directory via IIS. If you want to be able to see this information, you must enable Execute access at the Home Directory level on IIS, or move the script to a directory that has Execute access.
You can obtain several pieces of information about each array member from the array member status lines. Table 2 dissects the following status entry:
Proxy2 192.168.1.50 80 http://proxy2:80array.dll MSProxy/2.0 12542 Up 100 100
Routing Within an Array
If you have an array configuration within a hierarchy, as illustrated in Figure 4, you would probably want the array members to route requests among the array members before sending them to the Internet. In this case, you should be sure to check the “Routing within array” checkbox on the Web Proxy Service dialog box Routing tab (Figure 2). Routing within an array is performed by the Cache Array Routing Protocol (CARP), which is discussed in the following section.
To enable routing within an array, follow these steps:
Open the Internet Service Manager.
Double-click the Web Proxy service.
Click the Routing tab.
In the “Routing within array” section, click the “Resolve Web Proxy requests within array before routing upstream” checkbox.
You can click the Advanced button to configure the following options (Figure 8):
TTL setting: Lets you configure how often array members and downstream Proxy Servers update their internal membership tables.
Use credentials to communicate within array: Lets you set user credentials for upstream routing, in case the upstream proxy server doesn’t allow anonymous access. You can configure a username, password, and authentication type as Basic or NT CR.
Intra-array communication: If the proxy server has multiple network adapters, you can specify which one to use when communicating with the array through this option. The Auto-detect button lets you cycle through the IP addresses of your network card.
Click OK to confirm changes on the Advanced Array Options dialog box.
Click OK to confirm the Routing tab changes.
If you receive a message that the Intra-array IP addresses do not match, click the Advanced button and use Auto-detect to choose a different IP address on the internal adapter. Click OK twice to confirm you selections.
Removing Array Members
You can remove an array member or leave an array via the Array dialog box (Figure 6). If you attempt to remove the proxy server that you’re using from the array, you must use the “Leave Array” button. If you want to remove a different proxy server from the array, you use the “Remove from array” button.
To remove an array member or to leave an array:
Open the Internet Service Manager.
Double-click any of the Proxy Server service icons.
Click the Array button.
If you’re on the proxy server that you would like to remove from the array, click the Leave Array button. If you want to remove another proxy server from the array, highlight the server in the Array Members window and click the “Remove from array button.”
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