Objectives

70-293: MCSE Guide to Planning a Microsoft Windows Server 2003

Network, Enhanced

Chapter 12: Planning and Implementing Server

Availability and Scalability

70-293: MCSE Guide to Planning a Microsoft Windows Server 2003 Network 2

Objectives

• Understand availability and scalability• Differentiate between server clustering and Network

Load Balancing• Implement server clustering• Describe the concepts involved in server clustering• Describe the concepts involved in Network Load

Balancing• Implement Network Load Balancing• Install applications on an NLB cluster


Availability and Scalability

• Availability: the percentage of time that servers are providing service on the network

• Scalability: the ability to expand the number of clients or data that a server can support

• How you implement availability and scalability depends on whether applications are stateful or stateless


Server Availability

• Potential causes of server or service failure• Hardware failure

• Network failure

• Administrator mistakes

• Operating system crashes

• Application crashes


Server Availability (continued)• To provide higher server availability, you can use:

• Redundant hardware (e.g., RAID5)

• Uninterruptible power supply for temporary power outages

• Backup power generator for longer power outages

• Redundant paths through the network

• Standardized procedures to perform tasks

• Fully document the network server configuration

• Regularly patched operating systems and applications

• Windows Server 2003 clustering to implement server clusters and Network Load Balancing


Scalability

• Scalability can be accomplished by:• Scaling up

• Scaling out

• To scale up, you can:• Add more RAM

• Add a faster disk subsystem

• Add more processors

• Scaling up can be both limiting and expensive


Scalability (continued)

• Scaling out uses commonly available hardware rather than specialized hardware• Difficult when a single service is running on a server and

you want to scale out

• Network Load Balancing (NLB)• Best solution for scaling out a single application

• Can distribute the load between multiple servers

• NLB can sense a failed server


Stateful and Stateless Applications

• Stateful applications require the server to retain knowledge about the client accessing the server• Not well suited to scale out

• Easier to scale up

• Stateless applications do not require the server to retain knowledge about the client accessing the server • Well suited to scale out


Windows Server 2003 Clustering

• Windows Server 2003 provides two clustering mechanisms to provide availability and scalability:• Server clusters

• NLB


Server Clusters

• Provides highly available services• A service runs on a single server and can be moved to

another server in the cluster (failover)• Server clusters are available only in Windows Server

2003, Enterprise Edition and Datacenter Edition• Up to eight nodes are supported in each server cluster

• Server clusters must have a shared storage


Server Cluster Configurations• Windows Server 2003 supports:

• Active/Passive• Consists of two nodes: one hosts services and the other does

not• N+I failover

• N nodes in the server cluster are active and I nodes are passive in the server cluster ready to accept failed over services

• Active/Active• Consists of two or more nodes, all of which are active

• Single node virtual server• Consists of only one node. and does not have failover

capability


Cluster Applications

• To use server clusters, application must be• An IP-based protocol

• Able to specify where application data is located

• Able to use the clustering API and receive status notifications and manage the cluster


Network Load Balancing

• Network Load Balancing (NLB) spreads application requests from clients among two or more servers

• With NLB, an application is installed on multiple servers using a virtual IP address

• NLB can spread network requests evenly among the servers hosting the application or spread network requests based on a weighting scheme


An Example of Windows Server 2003 Clustering

• The following example illustrates how both server clusters and NLB can be used for a Web-based application designed to explore a computerized web based database backed school registration system


An Example of Windows Server 2003 Clustering (continued)


Activity 12-1: Cluster Concepts

• The purpose of this activity is to learn more about server clusters and NLB


Installing and Configuring Server Clusters

• The cluster service is installed automatically as part of a Windows Server 2003 installation

• To configure a server cluster, you use Cluster Administrator• To create new server clusters or

• Add new nodes to an existing server cluster

• New Server Cluster Wizard: creates a new cluster• After installation, the current state of your cluster is

shown in Cluster Administrator


Activity 12-2: Installing a Single Node Virtual Server Cluster

• The purpose of this activity is to create a single node virtual server cluster


Server Cluster Concepts

• The various concepts about server clusters include:• Shared disks

• Quorum resource

• Cluster communication

• Resource groups

• Failover and failback

• Virtual servers


Shared Disks

• Shared disk: storage that all nodes in a cluster can access• Not required when a geographically dispersed server

cluster is configured with an alternate data synchronization mechanism, or when a server cluster has a single server for testing purposes

• When shared disks are required use either• A shared SCSI bus or

• Fibre Channel SAN


Shared SCSI Bus

• SCSI configuration requirements include• An SCSI card that can disable autobus reset• All SCSI devices on the SCSI must have unique SCSI IDs• Proper termination on the SCSI bus• SCSI hard drives that are multi-initiator enabled to support

multiple SCSI cards on the bus


Shared SCSI Bus (continued)


Fibre Channel

• Fibre Channel is for storage area networks • Requirements for Fibre Channel shared storage

• Fibre Channel card for each node in the server cluster

• External storage array that supports Fibre Channel

• Fibre Channel switch to connect the nodes to the external storage array


Fibre Channel (continued)


Quorum Resource

• Quorum Resource is used by the cluster service• To store configuration information

• To arbitrate which node owns the cluster

• The location is specified at server cluster creation• Only one node at a time can own the quorum resource• First available node becomes the owner


Cluster Communication

• Nodes in a server cluster communicate with each other using heartbeat packets

• Heartbeat packets monitor which nodes in the server cluster are still up and available• Can be UDP unicast packets or multicast packets


Resource Groups

• Control of services and applications in a server cluster is based on resource groups

• Resource group: logical grouping of all required resources for an application or service to run

• Resources can be disk partitions, IP addresses, printers, services, and applications

• Resources can be in the following states: online, offline, online pending, offline pending or failed


Failover and Failback

• If a server cluster node fails, the resource groups on that node automatically fail over to another node

• After failover has occurred, failback is possible• Occurs when the original node hosting a resource group is

available again and the resource group is moved back to the original node

• Can define whether a resource group fails back automatically, manually, or not at all


Virtual Servers

• Virtual server: collection of resources in a resource group presented by the cluster service

• The node that owns the group responds on its behalf • Resources in server clusters are always accessed

through a virtual server


Activity 12-3: Adding a Printer to a Virtual Server

• The purpose of this activity is to add a printer to a virtual server


Activity 12-4: Removing a Server Cluster Node

• The purpose of this activity is to remove the final node from a server cluster


Network Load Balancing Concepts

• Concepts in NLB include:• The NLB driver

• Virtual IP addresses

• Application requirements

• Affinity

• Load balancing options

• Network communication

• Port rules


NLB Driver

• NLB driver: software responsible for performing NLB on each host in an NLB cluster

• Operates between the network card driver and the IP protocol• Can intercept and filter all incoming IP traffic

• Filtering is required because all hosts in an NLB cluster share a MAC address that is used for the cluster


Activity 12-5: Enabling the NLB Driver

• The purpose of this activity is to enable the NLB driver


Virtual IP Address

• Each NLB cluster has a virtual IP address• The virtual IP address must be

• Unique on the network

• On the same subnet as the hosts in the NLB cluster

• Added as a secondary IP address to a network interface


Application Requirements

• NLB suitable applications must:• Must use TCP or UDP

• Data modified by the clients must be synchronized between hosts in the NLB cluster or stored in a central location, or affinity must be configured

• Session state information must be stored on client computers or central location, or affinity must be configured

• The application must not bind to a computer name

• Applications must not keep files open for writing


Affinity• Affinity: responses to requests made originally to one

host in an NLB cluster are directed back to the original host• Required for applications that track session state info

• Affinity can be configured in three ways:• None: affinity is not performed for stateless applications

• Single: affinity based on the source IP address of the client

• Class C: affinity is based on the source network of the client.


Load Balancing Options

• When hosts are part of an NLB cluster, you can define how the load is balanced between them:• Multiple Host and Equal

• NLB cluster distributes load evenly between all hosts in cluster

• Multiple Host and Load weight• NLB cluster distributes requests based on a load weight

• Single Host • All requests to the NLB cluster are directed to a single host


Network Communication• All hosts in the NLB cluster share a MAC address• All client requests use the MAC address of the NLB

cluster as the destination MAC address• Allows all hosts in the NLB cluster to receive packets

addressed to the NLB cluster

• NLB driver loaded on each host accepts or discards the packet based on an algorithm that takes into account affinity settings, load weighting, and priority

• NLB clusters can be configured to use either unicast MAC addresses or multicast MAC addresses


Unicast

• Unicast is the most common method used for distributing client requests

• When selected, all hosts in the NLB cluster use the same unicast MAC address

• Unicast MAC address is used in place of the MAC address embedded in the network card of each host


Multicast

• Multicast MAC addresses: prevent the inefficient use of switches and allow NLB cluster hosts with a single network to communicate among themselves


Port Rules

• Port rules• Control what the NLB driver does with packets

• When hosts in the NLB cluster receive packets from clients, port rules define what is done with each packet

• Composed of• Cluster IP address

• Port address range

• Protocol

• Filtering mode that includes load weight and affinity


Implementing Network Load Balancing

• To implement an NLB cluster• NLB driver must be enabled on all servers that are to be

hosts in the NLB cluster

• Can create a new NLB cluster using Network Load Balancing Manager (nlbmgr.exe)

• After the first host has created the NLB cluster, others can join


Activity 12-6: Installing an NLB Cluster

• The purpose of this activity is to install an NLB cluster


Installing Applications on an NLB Cluster

• No special procedure to use when installing applications on an NLB cluster

• Application must be installed on all hosts in cluster• Microsoft recommends that you automate the process

of application configuration to ensure that all servers are configured exactly the same


Activity 12-7: Configuring a Web Application for Load Balancing

• The purpose of this activity is to configure a Web site for load balancing


Activity 12-8: Removing an NLB Clustered Application

• The purpose of this activity is to remove an NLB cluster


Summary

• Availability: percentage of time that servers are providing service on the network

• Scalability: ability to expand the number of clients or data that a server can support

• Windows Server 2003 provides two clustering mechanisms to provide availability and scalability: server clusters and NLB

• In a server cluster a service runs on a single server and can be moved to another server (failover)


Summary (continued)

• Network Load Balancing (NLB) spreads application requests from clients among two or more servers

• NLB Manager is used to implement NLB• When implementing NLB, Microsoft recommends

that you automate the process of application configuration to ensure that all servers are configured exactly the same

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