Application
Microsoft Application Center 2000 Component Load Balancing Technology Overview
Author: Chris Rees
This technical overview will discuss Microsoft Application Center (Application Center) Component Load Balancing technology (CLB).
Introduction
Microsoft Application Center (Application Center) is part of the Enterprise server, and Enterprise server is a Microsoft company-launched. NET Part of the concept. Other members included in Enterprise server are: Commerce Server 2000, BizTalk Server 2000, and SQL Server 2000. For more information about. NET, see the site:
http://www.microsoft.com/net。
The purpose of application Center in. NET is to provide content deployment and management capabilities for WEB sites based on Windows 2000 and Internet information Services 5.0. Application Center makes WEB sites scalable, more robust, easier to manage, and more secure. The core idea is that many Web servers form a cluster, and for customers, the cluster is a Web site. The idea in conjunction with this is that a single application image that is replicated to all cluster members. The application image contains all the parts required for a business solution, including WEB sites, registry settings, files, COM + components, and so on. By reflecting the current state of the cluster's events, performance counters, and monitors, it is easy to monitor the operation of the cluster.
Application Center Cluster
With application Center, you can build multi-level clusters that can use a variety of load-balancing techniques. Load-balancing technology helps application Center provide scalability and stability. There are two types of load balancing technologies that are supported:
- Network Load Balancing (NLB)
- Component Load Balancing (CLB)
The topology of the application Center cluster determines how to support load-balancing technology. A typical application Center cluster topology is based on an n-tier solution that includes a Web-tier cluster to provide content services to clients. This Web-tier cluster uses IIS and Network Load Balancing (NLB) to satisfy incoming IP requests.
file:///F:/My%20Work/Technical Documentation/server group setup/MICROSOFT%20APPLICATION%20CENTER%202000%20 Component Load Balancing Technology Overview. files/clbovr01.gif
Figure 1 Typical topology of the application Center cluster
Software on a Web-tier cluster (ASP pages, and so on) can create and use COM + components on the local computer, or create and use COM + components on another remote computer by using distributed COM. If there is no CLB, the remote activity will be static because it has nothing to do with the workload already added to the remote server. This is the real purpose of CLB-to make COM + components installed on stand-alone server clusters reliable, scalable, and load-balanced.
Network Load Balancing
Network Load Balancing (NLB) is an IP load balancing technology that is part of Windows Advanced Server and Windows Data Center. With NLB, incoming TCP traffic, User Datagram Protocol (UDP) communications, and General Routing Encapsulation (GRE) communication requests are distributed to individual cluster members. Distribution is based on the statistical algorithm set up by the server load percentage. NLB provides dynamic scaling that automatically adapts to the addition and deletion of servers in the cluster without affecting the client. NLB is robust because it detects a server failure and silently deletes it from a running cluster.
Application Center greatly simplifies the management of NLB based clusters. The Application Center Cluster Creation Wizard automatically configures NLB settings. This is much simpler than the steps required to use Windows 2000 stand-alone. Application Center is also easy to add, remove, and put servers online/offline in the cluster.
For more information about NLB, check your site:
http://www.microsoft.com/windows2000/library/howitworks/cluster/nlb.asp。
Component Load Balancing
Component Load Balancing technology enables COM + components to load balance. COM + components are compiled software objects that can be used in a variety of different languages, including VBS, ASP, Visual Basic, and C + +. They provide a useful way to bind software to a convenient and reusable entity. In CLB, the COM + component is located on a server within a stand-alone COM + cluster. Calls designed to activate COM + components are evenly loaded on individual servers within the COM + cluster. As shown in Figure 1, the decision elements of the CLB software run on the WEB layer. Some CLB software that collects information does run on the COM + cluster.
Component Object Model
The root of the CLB is the component architecture, which is composed of the Component Object Model (COM). When you write object-based software based on this standard, the standard provides a common mechanism for making software services available. It allows software to be written in a variety of languages, in various operating systems. The key to achieving this flexibility is the COM interface.
The functionality of a COM component is implemented through one or more interfaces. To use a COM component, the client software must be written in a language that knows how to handle the interface. Languages such as visual Basic, ASP, VBS, JavaScript, and Visual C + + are all available. The interface itself is simply a table of numbers that holds the address of the method supported by the interface.
file:///F:/My%20Work/Technical Documentation/server group setup/MICROSOFT%20APPLICATION%20CENTER%202000%20 Component Load Balancing Technology Overview. files/clbovr02.gif
Figure 2 Interfaces on a COM component
Typically, a COM component is located in a dynamic-link library (DLL) or executable (. exe) file. They can be installed on the client or on a remote computer. When they are used remotely, the call is completed by the distributed COM (DCOM) mechanism based on remote procedure call (RPC).
COM + Services
COM + Services is part of the Windows 2000 operating system and provides a set of services based on COM and Microsoft Transaction Sever (MTS). COM + Services provides enterprise-class capabilities such as transaction support, object lifetime services, security services, events, queued components, and so on.
COM + components
COM + components are COM components that can take advantage of COM + services. One of the requirements for COM + components is that it will carry configuration information. Configuration information is a set of properties that enable the underlying COM architecture to identify whether a particular COM + service, such as transaction support, and the load balancing that we will refer to later, is supported.
COM + components are assembled into packages called "Applications", where applications are different from application Center applications. COM + applications are a set of COM + components, while the application Center application is a series of resources used in business solutions. Examples of this are WEB sites, files, COM + components, and registry keys.
How component Load Balancing works
CLB has two main parts:
- CLB software for COM + cluster load balancing.
- COM + cluster, a server cluster managed by Application Center, to activate and run COM + components. ）
CLB Software
The CLB software is responsible for determining the order in which COM + cluster members are used when activating COM + components.
The business logic used to create a COM + component runs on a Web-tier cluster. This is typically a Visual Basic ASP script that, when required to use COM + components, calls the
CreateObject。 (internal is converted to the
CoCreateInstance's call). When using CLB, instead of creating components on the local server, the routing list and server response schedules are used to help pass COM + component activation requests to a COM + cluster that is already a load-balanced implementation. The COM + cluster member then creates the component and returns an interface to the client machine. Once a component is created, CLB no longer operates on it.
Routing list
The routing list exists on each WEB-tier cluster member, which contains a list of COM + cluster members that need to be load balanced, as shown in Figure 3. In addition, the routing list also exists in a location called a COM + routing cluster. This location is for routing only, not for Web-tier functionality. This white paper will focus on the Web-tier scenario.
file:///F:/My%20Work/Technical Documentation/server group setup/MICROSOFT%20APPLICATION%20CENTER%202000%20 Component Load Balancing Technology Overview. files/clbovr03.gif
Figure 3 Routing list and response time
The routing list is initially created by an administrator on the Web-tier cluster controller, and then automatically synchronized with each cluster member. As a result, it is not possible (and actually not) to have the list of routes that a cluster member has that contains changes to COM + cluster members. One of the great advantages of having a routing list on each of the Web-tier cluster members is that it eliminates a single point of failure. If a Web-tier cluster member stops running (whether intentionally or not), other members will continue to load-balance the COM + cluster through their routing lists.
Response Schedule
Every 200 milliseconds, the CLB software running on each of the Web-tier cluster members polls each member of its own routing list. Since then, a table has been created in memory where COM + cluster members are listed in response Time hierarchy-the faster the members of the response, the higher their status in the table. WEB Layer members use the response schedule in a circular fashion to pass incoming activation requests to COM + cluster members. This means that when an activation request is received, the most responsive and least busy COM + cluster member is used first, and the second-fastest member is used to process the next request. When the response schedule is exhausted, the next request is sent to the first article in the table. The following activation requests are processed in turn. This situation continues until the response time is updated and the activation request is reset to the beginning of the new Load balancing table.
Each Web-tier cluster member has its own COM + cluster member response schedule. Do not attempt to keep these values synchronized within the entire WEB-tier cluster because the routing list replication speed does not keep up with the changes in the COM + cluster load.
COM + cluster
Within a Web-tier cluster, an administrator uses the Application Center Cluster Creation Wizard to create a COM + cluster. Each cluster member must have the same copy of the COM + component installed. There is a deployment wizard that you can use to install components. Once a component is created, it must know that it is within the CLB cluster.
COM + components that support clustering
In order to use CLB, COM + components must be written to confirm the situation they are in. The key issue is component status. In COM +, a component should not retain state information for each component, because it can have a negative impact on scalability and transaction management. Scalability is affected by the fact that if the component is stateful, it cannot be recycled. Transaction management is more complex because the state of each component cannot cross the transaction boundary. There are other factors to consider when using CLB. Essentially, you don't have to worry about the location of the member nodes, because you can create components on any member of the CLB cluster. For example, in COM +, the entire process store can be used to store information that is useful for multiple components running on a server. Using this technology within a COM + cluster requires careful management because there is no guarantee that a component will be created on which member. As a result, subsequent reactivation of the component may occur on other cluster members. This causes the component to lose access to the entire process store on the previous member.
The component state should either be saved as a permanent state (such as a DBMS) so that it can be accessed from any cluster member, or it should be saved on the client (such as the Cookie information stored on the Internet client).
set up component load Balancing
The following are the steps required to establish a COM + cluster. These steps are based on the functionality in application Center Beta 2.
- set up the cluster .
CLB requires two clusters. A cluster is used to save a list of routes, which is typically located on a Web-tier cluster, as described earlier. Another cluster is a COM + cluster. See "Creating Cluster" (creating a cluster) in the online Help.
- Deploy the COM + component to a COM + cluster.
By using the Deployment Wizard, you can deploy the application Center application to another cluster. This is useful for a transition cluster that is used to deploy the updated content to a running cluster. See Figure 4. Typically, you run the wizard from a stager (transition server) that has a COM + component packaged in the application Center application. See "Synchronizing and Deploying Content" in the online Help.
file:///F:/My%20Work/Technical Documentation/server group setup/MICROSOFT%20APPLICATION%20CENTER%202000%20 Component Load Balancing Technology Overview. files/clbovr04.gif
Fig. 4 stager in Application Center
note By default, COM + components are not deployed because component deployment requires that the target IIS service be restarted and may cause the computer to reboot. However, the Deployment Wizard provides an option to force the COM + component deployment.
This makes it important to avoid the entire cluster outage during component deployment. This requires a phased deployment, allowing cluster members to go offline, update, and then online. For more information on this issue, see Microsoft application Center Resource Kit.
- Deploying COM + components to a Web-tier cluster
CLB requires that COM + components be installed on each of the Web-tier cluster members. Again, you can use the Deployment Wizard to do this. You can package COM + components into a application Center application that has been deployed to a WEB site. Remember, however, that COM + component deployment will require the IIS service to be restarted. Therefore, staging component deployment is important to ensure that Web sites are always available. Another noteworthy point is that the Web-tier cluster component deployment needs to be synchronized with the COM + cluster. Otherwise, when the Web site is active, the Web-tier cluster and the COM + cluster may have different versions of the components installed. For more information, see Microsoft application Center Resource Kit.
- To mark the Web-tier COM + component as supporting CLB
COM + components on a Web-tier cluster need to be marked to support CLB. This is done through the Component Services Explorer already in the application Center snap-in. The way to mark a component is to find it in the COM + application that contains it, select the Activation tab on the property page, and then select the Component supports dynamic load balancing check box.
- Create a routing list
The routing list is created on the Web-tier cluster controller and is automatically synchronized across the entire web-tier cluster. You can add a COM + cluster member list through the component Services tab on the Web-tier cluster Properties page in Application Center.
That's it. Once everything is installed, the WEB layer software running on behalf of the client will use COM + components within the COM + cluster, and the location of the COM + component will not affect this operation.
