Clustering Clustering ServersServers

ChapterSeven

Exam Objectives in this Chapter: Plan services for high availability

Plan a high availability solution that uses clustering services

Plan a high availability solution that uses Network Load Balancing

Implement a cluster server Recover from cluster node failure

Manage Network Load Balancing. Tools might include the Network Load Balancing Manager and the WLBS cluster control utility

Lessons in this Chapter: Understanding Clustering Using Network Load Balancing Designing a Server Cluster

Understanding Clustering A cluster is a group of two or more servers

dedicated to running a specific application (or applications) and connected to provide fault tolerance and load balancing.

Clustering is intended for organizations running applications that must be available, making any server downtime unacceptable.

In a server cluster, each computer is running the same critical applications, so that if one server fails, the others detect the failure and take over at a moment’s notice. This is called failoverfailover.

Understanding Clustering When the failed node returns to service,

the other nodes take notice and the cluster begins to use the recovered node again. This is called failbackfailback.

Clustering capabilities are installed automatically in the Windows Server 2003 operating system.

Clustering Types Windows Server 2003 supports two

different types of clustering: Server clusters and Network Load Balancing (NLB).

Important Server clustering is intended to provide high

availability for applications, not data. Do not mistake server clustering for an alternative to data availability technologies, such as RAID (redundant array of independent disks) and regular system backups.

Server Clusters Server clusters are designed for

applications that have long-running in-memory states or large, frequently changing data sets.

These are called stateful applications, and include database servers such as Microsoft SQL Server, e-mail and messaging servers such as Microsoft Exchange, and file and print services.

Server Clusters In a server cluster, all the computers (called

nodes) are connected to a common data set, such as a shared SCSI bus or a storage area network.

Example of a simple two-node cluster:

Server ServerNAS

Server Clusters A server cluster has its own name and Internet

Protocol (IP) address, separate from those of the individual computers in the cluster.

Therefore, when a server failure occurs, there is no apparent change in functionality to the clients, which continue to send their requests to the same destination.

The passive node takes over the active role almost instantaneously, so there is no appreciable delay in performance.

Network Load Balancing Network Load BalancingNetwork Load Balancing (NLB) is another type

of clustering that provides high availability and high reliability, with the addition of high scalability as well.

NLB is intended for applications with relatively small data sets that rarely change (or may even be readonly), and that do not have long-running in-memory states.

These are called stateless applicationsstateless applications, and typically include Web, File Transfer Protocol (FTP), and virtual private network (VPN) servers.

Network Load Balancing and Replication Network Load Balancing is clearly not

suitable for stateful applications such as database and e-mail servers.

It is possible to replicate data between the servers in an NLB cluster, for example, to prevent administrators from having to copy modified Web pages to each server individually. However, this replication is an occasional event, not an ongoing occurrence.

Network Load Balancing and Replication Network Load Balancing provides

scalability in addition to availability and reliability, because all you have to do when traffic increases is add more servers to the cluster.

Exam Tip Be sure you understand the differences

between a server clusterserver cluster and a NetworkNetworkLoad Balancing clusterLoad Balancing cluster, including the hardware requirements, the difference between stateful and stateless applications, and the types of clusters supported by the various versions ofWindows Server 2003.

Designing a Clustering Solution Clustering can provide a solution that

protects against three different types of failures: Software failures Hardware failures Site failures

Estimating Availability Requirements The degree of availability you require depends on

a variety of factors The nature of the applications The size Location Distribution of your user base,

The amount of availability an organization requires for its applications can affect its clustering configuration in several ways, including The type of clustering you use The number of servers in the cluster The distribution of applications across the servers in the

cluster, and The locations of the servers

Scaling Clusters There are two basic methods of increasing

cluster performance, which are as follows: Scaling up

Adding random access memory (RAM) or level 2 (L2) cache memory, upgrading to faster processors, and installing additional processors are all ways to scale up a computer

Scaling out Adding servers to an existing cluster

Real World Scalability in the Real World

Note page 7-8

How Many Clusters? If you want to deploy more than one

application with high availability, you must decide how many clusters you want to use.

Two Methods of Clustering Apps A cluster with two applicationsA cluster with two applications

Two separate clusters running two different Two separate clusters running two different applicationsapplications

App 1App 2

App 1App 2

App 1App 2

App 1App 2

App 1 App 1 App 2 App 2

Combining Clustering Technologies Two active notes sharing a single passive

node

NLB Cluster interacting with a server cluster

App 1App 1App 2 App 2

NLB Cluster

Server Cluster

Dispersing Clusters Deploying geographically dispersed clusters

enables applications to remain available in the event of a catastrophe that destroys a building or even a city.

Having cluster servers at different sites can also enable users to access applications locally, rather than having to communicate with a distant server over a relatively slow wide area network (WAN) connection.

Using Network Load Balancing Understanding Network Load Balancing

A Network Load Balancing cluster consists of up to 32 servers32 servers, referred to as hosts, each of which is running a duplicate copy of the application you want the cluster to provide to clients.

Network Load Balancing works by creating on each host a virtual network adaptervirtual network adapter that represents the cluster as a single entity.

Planning a Network Load Balancing Deployment NLB Network Design

InternetInternet

Internet router

Internet router

Firewall Firewall

Switch

Node Node Node Node

NLB Operational Modes The servers that are going to be the hosts in your

NLB cluster do not require any special hardware. Installing a second network interface adapter

Two operational modes: unicast mode and multicast mode.

In unicast mode, Network Load Balancing replaces the MAC address of the physical network interface adapter in each server with the MAC address of the virtual adapter representing the cluster.

The Address Resolution Protocol (ARP) resolves both of the server’s IP addresses (the IP address originally assigned to the network interface adapter and the cluster IP address) to the single MAC address for the cluster.

NLB and ARP ARP is a TCP/IP protocol that resolves IP addresses into MAC

or hardware addresses. To transmit to a particular IP address, a TCP/IP computer

must first discover the MAC address associated with that IP address, so that it can build a datalink layer protocol frame.

ARP functions by transmitting a broadcast message containing an IP address to the local network.

ARP requests that contain either its original IP address or the cluster IP address by sending a response containing the cluster MAC address.

Therefore, no computer on the network can transmit to the MAC address assigned for NLB server’s physical network interface adapter.

NLB and ARP Because the network interface adapters of

all the servers in the cluster have the same MAC address, the cluster servers cannot communicate among themselves in the normal way, using their individual MAC addresses.

Note table 7-1 on page 18

NLB Networking Important

A single computer running Windows Server 2003 cannot be a member of a Network Load Balancing cluster and a server cluster at the same time, because these two clustering solutions use network interface adapters in different ways.

If you want to deploy both an NLB cluster and a server cluster on your network, you must use separate servers for each cluster.

NLB Networking Note

Because all the servers in the cluster are using the same cluster MAC address, transmitting the heartbeats is simply a matter of directing the packets to that address.

The servers don’t need to broadcast the heartbeat messages, reducing the impact of the cluster traffic on the network.

Deploying a Network Load Balancing Cluster The basic steps in deploying NLB for a cluster of

Web servers on a perimeter network are found on page 7-20.

Monitoring Network Load Balancing Using Network Load Balancing Manager

Monitoring Network Load Balancing Using Event Viewer

Using Nlb.exe A command line using a utility

Some of the program’s most useful parameters are as follows:

display drain port drainstop params

Example print out on pages 23 – 24. query queryport port

Exam Tip Be sure to understand that the NLB.EXENLB.EXE

and WLBS.EXEWLBS.EXE programs are one andthe same, with identical functions and parameters

Practice: Creating a Network Load Balancing Cluster

Exercise 1: Installing IIS Page 7-25

Exercise 2: Creating a Network Load Balancing Cluster

Page 7-26 Exercise 3: Testing the Cluster

Page 7-28

Designing a Server Cluster Designing a Server Cluster Deployment

Planning a Server Cluster Hardware Configuration Using SCSI Understanding SCSI Using Fibre Channel Fibre Channel Arbitrated Loop Fibre Channel Switched Fabric

Using SCSI

Server Server Storage Storage

Cluster using a SCSI bus

Fibre Channel Arbitrated Loop

Server Server

Storage Storage

Cluster using a Fibre Channel arbitrated Loop

Fibre Channel Switched Fabric

Storage Storage

Server Server Server Server

Fibre Channel Switch

Cluster using a Fibre Channel switched fabric

Creating an Application Deployment Plan Windows Server 2003 can host the

following two basic types of applications in a server cluster: Single-instance applications Multiple-instance applications

Deploying Multiple-Instance Applications Partitioning an application means that you

split the application’s functionality into separate instances and deploy each one on a separate cluster node.

Database

A to G H to L M to S T to Z

Server Server Server Server

Selecting a Quorum Model Server clusters running Windows Server

2003 support the following three types of quorum models: Definitions on page 7-38 Single-node cluster Single-quorum device cluster Majority node set cluster

Exam Tip Be sure to understand the differences

between the various quorum models supported by Windows Server 2003.

Creating a Server Cluster To create a new

cluster, you must have the following information available: The name of the

domain in which the cluster will be located

The host name to assign to the cluster

The static IP address to assign to the cluster

The name and password for a cluster service account

Creating a Server Cluster Some of the configuration tasks you can

perform in Cluster Administrator are as follows: Create resource groups Define resource dependencies Configure the cluster network role Configure failover relationships

Exam Tip It is a good idea to spend some time

exploring the Network Load Balancing Manager and Cluster Administrator applications. Learn the function of each parameter or setting in these two programs, using the online help for assistance.

Configuring Failover Policies Some of the failover policies you might

consider using are as follows: Failover pairs Hot-standby server N+I Failover ring Random

Practice: Creating a Single Node Cluster

Exercise 1: Creating a Server Cluster Page 7-42

Exercise 2: Creating a Cluster Resource Page 7-43

Exercise 3: Access the Server Cluster Page 7-44

Summary Case Scenario Exercise

Page 7-46 Troubleshooting Lab

Page 7-48 Exam Highlights

Page 7-49 Key Points Key Terms