Your network consists of a single Active Directory domain. All servers run Windows Server 2008 R2.
You plan to publish a Web site on two Web servers. You need to deploy an availability solution for
your Web servers that meets the following requirements:
• Supports the addition of more Web servers without interrupting client connections
• Ensures that the Web site is accessible even if a single server fails
What should you do?
A.
Configure a failover cluster.
B.
Configure a Web garden on each Web server.
C.
Create a Network Load Balancing cluster.
D.
Create two Application pools on each Web server.
Explanation:
Windows Web Server 2008
Windows Web Server 2008 is designed to function specifically as a Web applications server. Other
roles, such as Windows Deployment Server and Active Directory Domain Services, are not supported
on Windows Web Server 2008. You deploy this server role either on a screened subnet to support a
Web site viewable to external hosts or as an intranet server. As appropriate given its stripped-down
role, Windows Web Server 2008 does not support the high-powered hardware configurations that
other editions of Windows Server 2008 do.
Windows Web Server 2008 has the following properties:
■The 32-bit version (x86) supports a maximum of 4 GB of RAM and 4 processors in SMP
configuration.
■The 64-bit version (x64) supports a maximum of 32 GB of RAM and 4 processors in SMP
configuration.
■Supports Network Load Balancing clusters.
You should plan to deploy Windows Web Server 2008 in the Server Core configuration, which
minimizes its attack surface, something that is very important on a server that interacts with hosts
external to your network environment. You should only plan to deploy the full version of Windows
Web Server 2008 if your organization’s Web applications rely on features such as ASP.NET, because
the .NET Framework is not included in a Server Core installation.
Configuring Windows Network Load Balancing
While DNS Round Robin is a simple way of distributing requests, Windows Server 2008 NLB is a much
more robust form of providing high availability to applications. Using NLB, an administrator can
configure multiple servers to operate as a single cluster and control the usage of the cluster in near
real-time.
NLB operates differently than DNS Round Robin in that NLB uses a virtual network adapter on each
host. This virtual network adapter gets a single IP and media access control (MAC) address, which is
shared among the hosts participating in the load-balancing cluster. Clients requesting services from
an NLB cluster have their requests sent to the IP address of the virtual adapter, at which point it can
be handled by any of the servers in the cluster.NLB automatically reconfigures as nodes are added and removed from the cluster. An administrator
can add and remove nodes through the NLB Manager interface or the command line. For example,
an administrator might remove each node in turn to perform maintenance on the nodes individually
and cause no disruption in service to the end user.
Servers within NLB clusters are in constant communication with each other, determining which
servers are available with a process known as heartbeats and convergence. The heartbeat consists of
a server participating in an NLB cluster that sends out a message each second to its NLB-participating
counterparts.
When five (by default) consecutive heartbeats are missed, convergence begins. Convergence is the
process by which the remaining hosts determine the state of the cluster.
During convergence, the remaining hosts listen for heartbeats from the other servers to determine
the host with the highest priority, which is then selected as the default host for the NLB cluster.
Generally, two scenarios can trigger convergence. The first is the missed heartbeat scenario
mentioned earlier; the second is removal or addition of a server to the cluster by an administrator.
The heartbeat is reduced by one half during convergence. A less common reason for convergence is
a change in the host configuration, such as a host priority.