Understanding high availability

High availability is an architectural design approach and associated service implementation that is used to guarantee the reliability of a service. Availability is directly associated with the uptime and usability of a service. This means that the downtime should be reduced to achieve an agreement on that service.

We can distinguish between two kinds of downtimes:

• Scheduled or planned downtimes

• Unscheduled or unexpected downtimes

To distinguish between scheduled downtimes, we can include:

• System patching

• Hardware expansion or hardware replacement

• Software maintenance

• All that is normally a planned maintenance task

Unfortunately, all these downtimes will interrupt your service, but you have to agree that they can be planned into a maintenance window that is agreed upon.

The unexpected downtime normally arises from a failure, and it can be caused by one of the following reasons:

• Human error

• Hardware failure

• Software failure

• Physical events

Unscheduled downtimes also include...