FAILOVER CLUSTER

Submitted by : Chinmoy jena

OVERVIEW OF CLUSTERWhat is a Cluster?

• Group of independent servers interconnected through a dedicated network to work as one centralized data processing resource.

• Clusters are capable of performing multiple complex instructions by distributing workload across all connected servers.

• Clustering improves the system's availability to users, its aggregate performance, and overall tolerance to faults and component failures.

NETWORK LOAD BALANCING• Enables high availability and scalability for Internet server-based

applications• Enables clients to access two or more servers using a single

IP address • Requires all servers in the NLB cluster to be running the same

server applications with the same configuration

What Is NLB?

Prerequisites of NLB cluster:

• All the host must be same subnet.• All the adapter should be configured as unicast or multicast.• Only TCP/IP protocol can be used on the adapter• All the adapters used with NLB must be configured with static IP.

HOW NLB WORKS• All servers in an NLB cluster are accessible by using a single (virtual) IP address

•Client requests are distributed across available servers in the NLB cluster based on a common algorithm

•All servers monitor each other through heartbeat messages

•If a server fails to send heartbeat messages for 5 seconds, the other servers automatically converge and redistribute the client connections across the available servers

HOW NLB WORKS

WHAT IS FAILOVER CLUSTER? Failover clusters in Windows Server 2012 provide a high-

availability solution for many server roles and applications.

Clustering remedies this situation by detecting hardware/software faults, and immediately restarting the application on another system without requiring administrative intervention, a process known as failover.

Without clustering, if a server running a particular application crashes, the application will be unavailable until the crashed server is fixed.

By implementing failover clusters, you can maintain application or service availability if one or more computers in the failover cluster fails.

Clusters usually use a heartbeat private network connection which is used to monitor the health and status of each node in the cluster.

DIFFERENCE BETWEEN FAILOVER CLUSTER AND NLB

A failover cluster is a group of servers that work together to maintain high availability of applications and services.

If one of the servers, or nodes, fails, another node in the cluster can take over its workload without any downtime (this process is known as failover).

There is use of cluster storage required to form failover cluster. Example: File server, DHCP server, MSSQL server

Network Load Balancing (NLB) is a feature that distributes network traffic among multiple servers or virtual machines within a cluster to avoid overloading any one host and improve performance.

There is no cluster storage required to form NLB. Example: Webserver

PREREQUISITES OF FAILOVER CLUSTER Server nodes should all have the same configuration and contain the same or

similar components. All tests in the Validate a Configuration Wizard must be passed.

Hardware Requirements

All nodes must run the same edition of Windows Server. All nodes must run the same processor architecture All nodes should have the same service pack and updates

Software Requirements

PREREQUISITES OF FAILOVER CLUSTER

The server should be connected to multiple networks for communication redundancy, or to a single network with redundant hardware, to remove single points of failure.

The network adapters should be identical and have the same IP protocol versions

Nodes in cluster must use DNS name resolution All servers in the cluster may be in the same Active Directory domain User account that creates the cluster must have administrator rights Failover cluster infrastructure recommendations: –

The same roles should be installed on each cluster node The AD DS role should not be installed on any of the cluster

nodes

Network Requirements

Infrastructure Requirements

FAILOVER CLUSTER COMPONENTS Node - A server that participates in a cluster

Resource - A device or service hosted on a cluster and accessed directly or indirectly by the application or end user

Network - This is a network across which cluster nodes can communicate with one another and with clients. There are three types of networks that can be used in a cluster.

Cluster storage -This is a storage system that is usually shared between cluster nodes.

Clients - These are computers or users that are using the Cluster service.

Witness - This can be a file share or disk that is used to maintain quorum. Ideally, the witness should be located in a network that is both logically and physically separate from those used by the failover cluster

FAILOVER CLUSTER COMPONENTS

FAILOVER AND FAILBACKFailover

Failover transfers the responsibility of providing access to resources in a cluster from one node to another.

Failover can occur when an administrator intentionally moves resources to another node for maintenance, or when unplanned downtime of one node happens because of hardware failure or other reasons

Failback

The Cluster service can failback instances that were originally hosted on the offline node after the offline node becomes active again.

When the Cluster service fails back an instance, it follows the same procedures that it performs during failover.

QUORUM Quorum is the number of elements that must be online for a cluster to continue

running.

In effect, each element can cast one vote to determine whether the cluster continues to run.

Each cluster node is an element that has one vote. In case there is an even number of nodes, then an additional element, which is known as a witness, is assigned to the cluster.

The witness element can be either a disk or a file share.

Each voting element contains a copy of the cluster configuration; and the Cluster service works to keep all copies synchronized at all times.

MODES OF QUORUM Node Majority (recommended for clusters with an odd number of nodes). Can

sustain failures of half the nodes (rounding up) minus one.

Node and Disk Majority (recommended for clusters with an even number of nodes). Can sustain failures of half the nodes (rounding up) if the disk witness remains online.

Node and File Share Majority (for clusters with special configurations). Works in a similar way to Node and Disk Majority, but instead of a disk witness, this cluster uses a file share witness.

No Majority: Disk Only (not recommended). Can sustain failures of all nodes except one (if the disk is online).

CLUSTER NETWORKS

CLUSTER STORAGE

TROUBLESHOOTING FAILOVER CLUSTERS

Reviewing cluster events (cluster, hardware, storage) and Cluster Logs(%systemroot%\cluster\reports\Cluster.log)

Use the Validate a Configuration Wizard

Review storage configuration

Check for group and resource failures (Get-clusterResources)

Check Cluster Resource (Get-ClusterNode)

Validation Report 2011.05.02 At 06.25.25.mht