Cluster Technology

Training – Sun L2 1Cluster TechnologyWI-RO Bangalore

Cluster Technology


Cluster

• A collection of loosely coupled computing nodes that provides a single client view of network services or applications.

• A cluster consists of multiple systems connected in various combinations to shared storage devices.

• Cluster is a highly available (HA) system, that is, a system that provides near continuous access to data and applications


Cluster Goals

• Reduce or eliminate system downtime because of software or hardware failure

• Ensure availability of data and applications to end users, regardless of the kind of failure that would normally take down a single server system

• Increase application throughput by enabling services to scale to additional processors by adding nodes to the cluster

• Provide enhanced availability of the system by enabling you to perform maintenance without shutting down the entire cluster


Cluster

• Sun Cluster (VCS)

• Veritas Cluster Server (VCS)


Sun Cluster

• Achieves high availability through a combination of hardware and software.

• Redundant cluster interconnects, storage, and public networks protect against single points of failure.

• The cluster software continuously monitors the health of member nodes and prevents failing nodes from participating in the cluster to protect against data corruption.

• The cluster monitors applications and their dependent system resources, and fails over or restarts applications in case of failures.


Sun Cluster

• Failover – Failover is the process by which the cluster

automatically relocates an application from a failed primary node to a designated secondary node.

– With failover, Sun Cluster provides high availability

• Scalability– Scalability provides constant response time or

throughput without regard to load. – A scalable application leverages the multiple nodes

in a cluster to concurrently run an application, thus providing increased performance.

– In a scalable configuration, each node in the cluster can provide data and process client requests


Sun Cluster Components

• Sun Cluster Software• Cluster Agents for application failover

• Cluster nodes with local disks (unshared)• Multihost storage (disks shared between

nodes)• Removable media (tapes and CD-ROM)• Cluster interconnect• Public network interfaces• Client systems• Administrative console• Console access devices


Sample Configuration


Cluster Node : A Host which is a Current or a Potential Member of Cluster.

Cluster Inter Connect : Private Network for Cluster-private communications, Data service Communications.

Public Network InterfacesClients connect to the cluster through the

public network interfaces


NAFO Group :Network Adapter Fail Over Group

PNM :Public Network Monitor (pnmd)

Client Systems:Client systems include workstations or other servers that access the cluster over the public network.

Client systems are not highly available. Data and applications on the cluster are highly available.


Administrative Console:The administrative console is not a cluster node. Use the administrative console for remote access to the cluster nodes, either over the public network, or through a Console Access Device

Console Access Device: Terminal Concentrator


•Sun Cluster Topologies

• A topology is the connection scheme that connects the cluster nodes to the storage platforms used in the cluster.

– Clustered pairs– N+1 (star)


Clustered Pairs Topology


Pair+M Topology


N+1 Topology


Sun Cluster Data Services

• iPlanet Web server.• Apache.• NFS.• DNS.• iPlanet LDAP server.• Oracle8i.• Oracle Parallel Server• Sybase• Netbackup.


VCS

• Building Blocks of VCS– clusters– resources and resource types– service groups– agents– communications (GAB and LLT)


Clusters

• A VCS cluster consists of multiple systems connected in various combinations to shared storage devices.

• All systems within a cluster have the same cluster ID.

• Connected by redundant private networks over which they communicate by heartbeats,

• Within a single VCS cluster, all nodes must run on the same operating system.


• Clusters can have from 1 to 32 member systems, or “nodes.”

• Applications can be configured to run on specific nodes within the cluster.

• Nodes that do not share storage cannot fail over an application that stores its data on disk.

• Multiple clusters can be managed from the command-line interface and from two cross-platform graphical user interfaces:– Cluster Manager (Java Console) – Cluster Manager (Web Console).


• Resources are hardware or software entities– network interface cards (NICs)– IP addresses– Applications– Databases

• Each resource is identified by a unique name.

• Resources with similar characteristics are known collectively as a resource type

Resources and Resource Types


Service Groups

• Smaller container for applications and associated resources is called a service group.

• VCS performs administrative operations on resources at the service group level.– Starting– Stopping– Restarting– monitoring.

• If a service group is to run on a particular server, all of the group’s required resources must be available to the server.

• Resources within a service group have dependencies


Resource Dependencies


Cluster Agents

• A program designed to control resources of a particular resource type.

• VCS includes a set of predefined resource types, and each has a corresponding agent, designed to control the resource.

• Application Cluster Agents are required to manage application failover– The application must have a defined procedure for

starting.– The application must have a defined procedure for

stopping.– The application must have a defined procedure for

monitoring the overall “health” of an individual instance.


Cluster Communications

• Cluster communications ensure VCS is continuously aware of the status of each system’s service groups and resources.

• Also enable VCS to recognize which systems are active members of the cluster, which are joining or leaving the cluster, and which have failed.



• On each cluster system, agents monitor the status of resources and communicate the status to the high-availability daemon, “HAD.”

• HAD communicates the status on the local system to other systems in the cluster via the Group Membership services/Atomic Broadcast protocol (GAB) and the Low Latency Transport (LLT).



• HAD

– The high-availability daemon– primary process running on each system.– Referred to as the “VCS engine.”– Receives information from various agents

regarding resources on the local system and forwards the information to each member system.

– Receives information from other cluster members, which it uses to update its own “view” of the cluster.

– HAD is monitored and, when required, restarted by a process called “hashadow,”


Cluster Communications• Low Latency Transport (LLT)

– A mechanism that provides communications between systems in a cluster.

– Provides fast, kernel-to-kernel communications.– Monitors network connections.– Serves as a replacement for the IP stack on systems– Runs directly on top of the Data Link Protocol Interface (DLPI)

layer. – LLT removes latency and overhead associated with the IP stack– LLT distributes (“load-balances”) internode communication

across private network links.• Maximum of eight Private network Link.

– LLT is responsible for sending and receiving heartbeat traffic over network links.

• Heartbeats are used to determine the “health” of nodes in the cluster.

– LLT informs GAB if communications to a peer are reliable or unreliable.


VCS Processes


VCS Administration

• CLI – Command Line Interface• Cluster Manager (Java Console)• Cluster Manager (Web Console)

Cluster Technology

Documents

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