What is cluster in linux server

Linux Clustering

A high availability Linux cluster is a group of Linux computers or nodes, storage devices that work together and are managed as a single system. In a traditional clustering configuration, two or more nodes are connected to shared storage (typically a SAN). With Linux clustering, an application is run on one node, and clustering software is used to monitor its operation. If the software detects an issue, it moves operation of the application to a secondary node in a process called failover. Since the secondary nodes shares storage with the primary, operation can continue quickly, meeting very short (seconds to minutes) recovery time and recovery point objectives.

Linux Open Source High Availability Clustering

Some Linux operating system vendors offer clustering software, such as SUSE Linux HAE; Red Hat Pacemaker; and Oracle Real Application Clusters (RAC). While they allow you to create a failover cluster, they present a variety of challenges. The HA configuration must include three related capabilities: data replication, failover clustering orchestration and a resource manager with a heartbeat monitor. With SUSE HAE and Red Hat Pacemaker, you are locked into one OS. If you want to use other less expensive or free OS versions, such as Oracle Enterprise Linux (OEL), you have to buy a separate HA solution. Creating a Linux clustering solution with open source OS solutions for high availability is highly manual and prone to human error.

Linux open-source HA extensions require a high degree of technical skill, creating complexity and reliability issues that challenge most operators.

To add replication needed to create a SANless clustering environment in a SUSE Linux Enterprise Server or Red Hat Enterprise Linux requires heavy custom scripting, which can take a long time to test and validate. It also requires retesting when any updates are made to the environment. Since these companies are operating system companies, their support is geared to operating system-level issues and limited HA expertise to help customers through the complexity of HA clustering.

Oracle RAC is a high availability solution architected for the database management tier. This means you need a different HA solution for those components that do the monitoring, management, and recovery of your application tiers. Oracle RAC requires you to make a costly upgrade from Oracle Database Standard Edition to Oracle Database Enterprise Edition in addition to paying for the RAC option – typically hundreds of thousands of dollars – when compared to SIOS LifeKeeper for Linux.

SIOS Protection Suite for Linux Clustering

SIOS LifeKeeper for Linux is sold in a purchasing bundle called SIOS Protection Suite for Linux that provides a tightly integrated combination of high availability failover clustering, continuous application monitoring, data replication, and configurable recovery policies, protecting your essential applications from downtime and disasters. While SIOS LifeKeeper for Linux can operate in a SAN environment to support a traditional HA hardware-based cluster, the architecture also enables a shared-nothing option to server clustering, allowing it to run SANless. It delivers a robust, versatile and easily configurable solution with automatic and manual failover/failback recovery policies for a wide variety of applications.

SIOS Protection Suite for Linux includes:

• SIOS LifeKeeper, which provides flexible SAN or SANless failover clustering software that monitors the entire application stack
• SIOS DataKeeper, which provides fast, efficient host-based, block-level data replication for mirroring local storage in a SANless cluster configuration or replicating to remote locations or cloud for disaster recovery
• Application Recovery Kits (ARKs) modules that provide application-specific, automated configuration, input validation, and reliable failover orchestration in accordance with application best practices

End-to-End Support from HA Experts

SIOS HA experts support customers throughout the process of selecting, testing, configuring and managing their HA clustering environment. SIOS HA experts are among the most well-trained, highly experienced support and customer experience teams in the industry with numerous certifications from cloud vendors such as Microsoft Azure and AWS.

In addition, SIOS LifeKeeper supports all major Linux distributions, including Red Hat Enterprise Linux, SUSE Linux Enterprise Server, Rock Linux, and Oracle Linux and accommodates a wide range of storage architectures. SIOS software has been adapted and optimized to run on these operating systems and the components are tested so ensure the SANless cluster solution will work on each OS.

Lastly, with the SIOS Protection Suite for Linux, you can run your essential applications in a flexible, scalable cloud environment, such as Amazon Web Services (AWS) without sacrificing performance, high availability, or disaster protection.

Linux Clustering in AWS

While cloud providers, such as AWS, provide high availability options, they do not provide the level of high availability and breadth of protection across the whole application infrastructure that customers demand and that you once achieved by using clusters before cloud computing. SIOS LifeKeeper for Linux achieves these desired levels of high availability for our mutual customers and the critical applications they are moving to the AWS cloud.

SIOS Protection Suite for Linux on AWS provides all the elements you need to create a high availability Linux cluster in a virtual private cloud (VPC) within a single AWS Region across two Availability Zones. It also supports out-of-the-box protection for SAP systems, Oracle databases, and other business-critical applications.

The SIOS Protection Suite Quickstart on the AWS Marketplace, helps you create a fully configured and operational Linux high availability cluster in a few short steps. It sets up an AWS architecture for SIOS Protection Suite for Linux and deploys it into your AWS account in about half an hour. This Quick Start, available is for enterprise users who want to deploy SIOS Protection Suite for Linux on AWS into their test or production environment.

SIOS Clustering for Linux

SIOS is a high availability company with 20+ years of delivering reliable, easy-to-manage HA for essential applications, such as SAP, SQL, Linux, Oracle. Its experience is built into its product, and installation and configuration take a fraction of the time and cost when compared to custom scripting required with the Linux distributions. In addition, SIOS tests and validates new versions of operating systems and applications so its customers don’t have to.

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Introduction and Advantages/Disadvantages of Clustering in Linux – Part 1

Hi all, this time I decided to share my knowledge about Linux clustering with you as a series of guides titled “Linux Clustering For a Failover Scenario“.

Following are the 4-article series about Clustering in Linux:

First of all, you will need to know what clustering is, how it is used in industry and what kind of advantages and drawbacks it has etc.

What is Clustering

Clustering is establishing connectivity among two or more servers in order to make it work like one. Clustering is a very popular technic among Sys-Engineers that they can cluster servers as a failover system, a load balance system or a parallel processing unit.

By this series of guide, I hope to guide you to create a Linux cluster with two nodes on RedHat/CentOS for a failover scenario.

Since now you have a basic idea of what clustering is, let’s find out what it means when it comes to failover clustering. A failover cluster is a set of servers that works together to maintain the high availability of applications and services.

For an example, if a server fails at some point, another node (server) will take over the load and gives end user no experience of down time. For this kind of scenario, we need at least 2 or 3 servers to make the proper configurations.

I prefer we use 3 servers; one server as the red hat cluster enabled server and others as nodes (back end servers). Let’s look at below diagram for better understanding.

Cluster Server: 172.16.1.250 Hostname: clserver.test.net node01: 172.16.1.222 Hostname: nd01server.test.net node02: 172.16.1.223 Hostname: nd02server.test.net 

In above scenario, cluster management is done by a separate server and it handles two nodes as shown by the diagram. Cluster management server constantly sends heartbeat signals to both nodes to check whether if anyone is failing. If anyone has failed, the other node takes over the load.

Advantages of Clustering Servers

1. Clustering servers is completely a scalable solution. You can add resources to the cluster afterwards.
2. If a server in the cluster needs any maintenance, you can do it by stopping it while handing the load over to other servers.
3. Among high availability options, clustering takes a special place since it is reliable and easy to configure. In case of a server is having a problem providing the services furthermore, other servers in the cluster can take the load.

Disadvantages of Clustering Servers

1. Cost is high. Since the cluster needs good hardware and a design, it will be costly comparing to a non-clustered server management design. Being not cost effective is a main disadvantage of this particular design.
2. Since clustering needs more servers and hardware to establish one, monitoring and maintenance is hard. Thus increase the infrastructure.

Now let’s see what kind of packages/installations we need to configure this setup successfully. The following packages/RPMs can be downloaded by rpmfind.net.

1. Ricci (ricci-0.16.2-75.el6.x86_64.rpm)
2. Luci (luci-0.26.0-63.el6.centos.x86_64.rpm)
3. Mod_cluster (modcluster-0.16.2-29.el6.x86_64.rpm)
4. CCS (ccs-0.16.2-75.el6_6.2.x86_64.rpm)
5. CMAN(cman-3.0.12.1-68.el6.x86_64.rpm)
6. Clusterlib (clusterlib-3.0.12.1-68.el6.x86_64.rpm)

Let’s see what each installation does for us and their meanings.

1. Ricci is a daemon which used for cluster management and configurations. It distributes/dispatches receiving messages to the nodes configured.
2. Luci is a server that runs on the cluster management server and communicates with other multiple nodes. It provides a web interface to make things easier.
3. Mod_cluster is a load balancer utility based on httpd services and here it is used to communicate the incoming requests with the underlying nodes.
4. CCS is used to create and modify the cluster configuration on remote nodes through ricci. It is also used to start and stop the cluster services.
5. CMAN is one of the primary utilities other than ricci and luci for this particular setup, since this acts as the cluster manager. Actually, cman stands for CLUSTER MANAGER. It is a high-availability add-on for RedHat which is distributed among the nodes in the cluster.

Read the article, understand the scenario we’re going to create the solution to, and set the pre-requisites for the implementation. Let’s meet with the Part 2, in our upcoming article, where we learn How to install and create the cluster for the given scenario.

References:

Keep connected with Tecmint for handy and latest How To’s. Stay Tuned up for the part 02 (Linux Servers clustering with 2 Nodes for a failover scenario on RedHAT/CentOS – Creating the cluster) soon.

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