Session 6: High-Availability and Cluster Resource Management

OVERVIEW

High-Availability, commonly referred as HA, and Cluster Resource Manager or CRM both facilitate the monitoring of the system's hardware and software failures. They works when one of the connected hosts experience failure, the other will act as a substitute to work on the process of that failed host is working on. So basically, HA and CRM will salvage the running process of a failed certain node via the other node connected to that said failed node. This activity will focus on the concepts of HA and CRM, and on their processes on how they work on the computers.

PROBLEM STATEMENT

A research about HA and CRM is needed to conduct this activity. Definitions, installation and configure, and diagrams of both processes are needed to understand them thoroughly. After the research, both HA and CRM should be installed in the student's computer for future purposes concerning both processes.

GUIDES ON SOLVING THE PROBLEM

HIGH_AVAILABILITY (HA) with Heartbeat

*Definition and Technicalities

High-Availability (HA) refers to a system or a component that is continuously operational for a desirably long length of time. According to Wikipedia, HA is a system design approach and associated service implementation that ensures a prearranged level of operational performance will be met during a contractual measurement period. It can be measured relative to "100% operational" or "never failing". HA focuses on the backup and failover processing and data storage and access. Data storage can be redundant array of independent disks (RAID) or storage area network (SAN).

*Installation and Configuration of Heartbeat

I used the command $ sudo-apt get install heartbeat to install Heartbeat in my computer.

Installation of Heartbeat

*Heartbeat Configuration Files

The configuration files can be found at /etc/ha.d directory.

Some configuration files are as follows:

- ha.cf : It is the configuration file for Heartbeat cluster messaging layer. It lists the communication facilities enabled between nodes, enables or disables certain features, and optionally lists the cluster nodes by host name.

- authkeys : It is the authentication file for Heartbeat cluster messaging layer. It enables Heartbeat to securely authenticate cluster nodes.

[Reference: http://linux.die.net/man/5/authkeys]

[Reference: http://linux.die.net/man/5/ha.cf]

*Illustrations and Diagrams

High-Availability Cluster Network Diagram

This diagram shows the HA cluster. It involves two nodes (at least) to support continuous service if a node fails. The other node will support the node's failure, and continue the service.

To be able to run HA cluster environment, an application must be able to use shared storage (SAN/NAS), must store all of its state until the last state before its failure at a non-volatile shared storage, must have a command line interface or scripts to control the application, and must not corrupt data if the application crashes.

CLUSTER RESOURCE MANAGER (CRM) with Pacemaker

*Definition and Technicalities

Cluster Resource Manager (CRM) monitors the system for both hardware and software failures. Pacemaker, a cluster resource manager detects and help recover machines and applications from failures. It supports maximum availability of a cluster by detecting and recovering from node and resource-level failures by making use of the messaging and membership capabilities provided by a cluster infrastructure (like Heartbeat). Pacemaker automatically recover your application and make sure it is available from one of the remaining machines in the cluster. After failure, it uses advanced algorithms to quickly determine the optimum locations for services based on relative node preferences and requirement with other cluster services.

[Reference: clusterlabs.org/wiki/Pacemaker]

*Illustrations and Diagrams

This type of configuration allows two nodes to be active or passive using Pacemaker and DRBD, which is cost-effective solution for many high-availability situations. Once the active nodes fail, passive node will act as its substitute.

*HA and CRM to a 3-year old child (Simple Explanation)
High-Availability Definition

High-Availability works, for example, when your toy car or your toy house castle lasts for how many years of you playing with it. It means that the parts of that toy car or toy house castle are well-designed fort to last that long, given that you've played with it very well.

Cluster Resource Manager Definition
For example, when you play your music box or the music player in your house, and suddenly it makes a screeching sound. And then after a few seconds or a few minutes, it went back to its normal behaviour, and play the music beautifully. That's how Cluster Resource Manager works. It recovers from its failure to play the music normally once the music or the music player detects what is wrong with its mechanism.

*Note: The implementation of HA and CRM will be tackled next laboratory session.

LEARNING AND INSIGHTS

Apache, Heartbeat, and Pacemaker create High-Availability on web servers. They make sure that when one node in a network fail to execute a process, another node from that same network will continue to execute that process.  In this sense, it can be implied that the process needed to be execute will push through.

CONCLUSION

Basically, the activity is to research the given questions in the laboratory, and install and configure Heartbeat and Pacemaker in the computer. Though it is difficult to explain the technicalities of the processes in simple words, it can be done because of the help of the diagrams showing how HA and CRM works.