Appendix C Designing Highly Available Cluster Applications

Table of Contents

Automating Application Operation

Insulate Users from Outages
Define Application Startup and Shutdown

Controlling the Speed of Application Failover

Replicate Non-Data File Systems
Use Raw Volumes
Evaluate the Use of JFS
Minimize Data Loss
Use Restartable Transactions
Use Checkpoints
Design for Multiple Servers
Design for Replicated Data Sites

Designing Applications to Run on Multiple Systems

Avoid Node-Specific Information
Avoid Using SPU IDs or MAC Addresses
Assign Unique Names to Applications
Use uname(2) With Care
Bind to a Fixed Port
Bind to Relocatable IP Addresses
Give Each Application its Own Volume Group
Use Multiple Destinations for SNA Applications
Avoid File Locking

Restoring Client Connections

Handling Application Failures

Create Applications to be Failure Tolerant
Be Able to Monitor Applications

Minimizing Planned Downtime

Reducing Time Needed for Application Upgrades and Patches
Providing Online Application Reconfiguration
Documenting Maintenance Operations

This appendix describes how to create or port applications for high availability, with emphasis on the following topics:

Designing for high availability means reducing the amount of unplanned and planned downtime that users will experience. Unplanned downtime includes unscheduled events such as power outages, system failures, network failures, disk crashes, or application failures. Planned downtime includes scheduled events such as scheduled backups, system upgrades to new OS revisions, or hardware replacements.

Two key strategies should be kept in mind:

Design the application to handle a system reboot or panic. If you are modifying an existing application for a highly available environment, determine what happens currently with the application after a system panic. In a highly available environment there should be defined (and scripted) procedures for restarting the application. Procedures for starting and stopping the application should be automatic, with no user intervention required.
The application should not use any system-specific information such as the following if such use would prevent it from failing over to another system and running properly:
- The application should not refer to uname() or gethostname().
- The application should not refer to the SPU ID.
- The application should not refer to the MAC (link-level) address.

Appendix C Designing Highly Available Cluster Applications

Technical documentation

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