VCS Building Blocks. Topic 1: Cluster Terminology After completing this topic, you will be able to define…

VCS Building Blocks

Topic 1: Cluster Terminology

After completing this topic, you will be able to define clustering terminology.

A Nonclustered Computing Environment

Definition of a Cluster

A cluster is a collection of multiple independent systems working together under a management framework for increased service availability.

Application

Node

Storage

Cluster Interconnect

Definition of VERITAS Cluster Server and Failover

VCS detects faults and performs automated failover.

Application

Node

Failed Node

Storage

Cluster Interconnect

Definition of an Application Service

An application service is a collectionof all the hardware and software components required to provide a service. If the service must be migrated to

another system, all components need to be moved in an orderly fashion.

Examples include Web servers, databases, and applications.

Definition of a Service Group

A service group is a virtual containerthat enables VCS to manage an application service as a unit. All components required to

provide the service, and the relationships between these components, are defined within the service group.

A service group has attributes that define its behavior, such as where it can start and run.

Service Group Types Failover:

– The service group can be online on only one cluster system at a time.

– VCS migrates the service group at the administrator’s request and in response to faults.

Parallel– The service group can be online on multiple cluster

systems simultaneously.– An example is Oracle Real Application Cluster (RAC).

HybridThis is a special-purpose type of service group used to manage service groups in replicated data clusters (RDCs). RDCs use replication between systems at different sites instead of shared storage.

Definition of a ResourceResources are VCS objects that correspond to thehardware or software components of an applicationservice. Each resource must have a unique name throughout the

cluster. Choosing names that reflect the service group name makes it easy to identify all resources in that group, for example, WebIP in the WebSG group.

Resources are always contained within service groups. Resource categories include:

– Persistent None (NIC) On-only (NFS)

– NonpersistentOn-off (Mount)

Resource DependenciesResources in a service group have a defined dependency relationship, which determines theonline and offline order of the resource. A parent resource depends

on a child resource. There is no limit to the

number of parent and child resources.

Persistent resources, such as NIC, cannot be parent resources.

Dependencies cannot be cyclical.

Parent/child

Child

Parent

Resource AttributesResource attributes definean individual resource. The attribute values are

used by VCS to manage the resource.

Resources can have required and optional attributes, as specified by the resource type definition.

mount –F vxfs /dev/vx/dsk/WebDG/WebVol /Web

WebMount resource

Solaris

Resource TypesResources are classifiedby type. The resource type

specifies the attributes needed to define a resource of that type.

For example, a Mount resource has different properties than an IP resource.

mount [-F FSType] [options] block_device mount_point

Solaris

Agents have one or more entry points that perform a set of actions on resources.

Each system runs one agent for each active resource type.

Agents: How VCS Controls ResourcesEach resource type has a corresponding agent process that manages all resources of that type.

online

offline

monitor

clean

NIC

eri0

IP

10.1.2.3

Mount

/web /log

Volume

WebVol logVol

Disk Group

WebDG

Topic 2: Cluster Communication

After completing this topic, you will be able to describe cluster communication mechanisms.

Cluster Communication

The cluster interconnectserves to: Determine which systems are

members of the cluster using a heartbeat mechanism.

Maintain a single view of the status of the cluster configuration on all systems in the cluster membership.

A cluster interconnect provides a communicationchannel between cluster nodes.

Low-Latency Transport (LLT)

LLT

LLT

LLT: Is responsible for sending

heartbeat messages Transports cluster

communication traffic to every active system

Balances traffic load across multiple network links

Maintains the communication link state

Is a nonroutable protocol Runs on an Ethernet

network

Group Membership Services/Atomic Broadcast (GAB)

GAB: Performs two functions:

– Manages cluster membership; referred to as GAB membership

– Sends and receives atomic broadcasts of configuration information

Is a proprietary broadcast protocol

Uses LLT as its transport mechanism

LLTLLT

GAB LLT

GAB

The Fencing DriverFencing: Monitors GAB to detect

cluster membership changes

Ensures a single view of cluster membership

Prevents multiple nodes from accessing the same Volume Manager 4.x shared storage devices

LLT

GAB

Fence

Fence

LLT

GAB

Reboot

The High Availability Daemon (HAD) The VCS engine, the

high availability daemon:– Runs on each system

in the cluster– Maintains configuration

and state information for all cluster resources

– Manages all agents The hashadow daemon

monitors HAD.

HADhashadow

LLT

GAB

Fence

Comparing VCS Communication Protocols and TCP/IP

HADhashadow

LLT

GAB

iPlanet

NIC

TCP

IP

NIC

User Processes

Kernel Processes

Hardware

Topic 3: Maintaining the Cluster Configuration

After completing this topic, you will be able to describe how the cluster maintains the configuration.

Maintaining the Cluster Configuration HAD maintains a

replica of the cluster configuration in memory on each system.

Changes to the configuration are broadcast to HAD on all systems simultaneously by way of GAB using LLT.

The configuration is preserved on disk in the main.cf file.

HADmain.cf hashadow

HADhashadow

VCS Configuration Files

include "types.cf"cluster vcs (

UserNames = { admin = ElmElgLimHmmKumGlj }Administrators = { admin }CounterInterval = 5)

system S1 ()

system S2 ()

group WebSG (SystemList = { S1 = 0, S2 = 1 })Mount WebMount (

MountPoint = "/web"BlockDevice = "/dev/vx/dsk/WebDG/WebVol"FSType = vxfsFsckOpt = "-y")

main.cf

A simple text file is used to store the cluster configuration on disk.

The file contents are described in detail later in the course.

Topic 4: VCS Architecture

After completing this topic, you will be able to describe the VCS architecture.

VCS Architecture Agents monitor resources on

each system and provide status to HAD on the local system.

HAD on each system sends status information to GAB.

GAB broadcasts configuration information to all cluster members.

LLT transports all cluster communications to all cluster nodes.

HAD on each node takes corrective action, such as failover, when necessary.

Topic 5: Supported Failover Configurations

After completing this topic, you will be able to describe the failover configurations supported by VCS.

Active/Passive

Before Failover After Failover

Active/Passive N-to-1

Before Failover

After Failover

Before Failover

After Repair

Active/Passive N + 1

After Failover

Standby Server

Standby Server

Active/Active

Before Failover After Failover

N-to-N

Before Failover

After Failover