High Availability and Disaster Recover.

 

Often, people are confused about high availability and disaster recovery because availability and disaster recovery will share some of the same common best practices, like monitoring issues, deploying to multiple locations, and automatic failover.

Availability is different from disaster recovery in terms of objective and focus. Availability is more concerned with ensuring high system  and application availability in a given time frame. Application availability is calculated by dividing uptime by the total sum of uptime and downtime. Disaster recovery is concerned with the recovery of applications, environments, and people from large-scale disasters. To determine the goal of disaster recovery, the two most important parameters, Recover Point Objective (RPO) and Recovery Point Objective (RTO), are used. 

Availability	Disaster Recover
High availability is about to eliminate single points of failure.	Disaster recovery is a process contains set of policies and procedures will trigger when loss of high availability
High availability helps us make sure our system is operational in identified failure scenarios.	Disaster recovery and business continuity planning address man-made disasters such as cyber attacks, terrorism attacks, human error, and natural disasters such as floods, hurricanes, earthquakes, and so on
Application availability is calculated by dividing uptime by the total sum of uptime and downtime.	Depending on the disaster, the following two main objectives will be defined:          Recover point objective (RPO): amount of data loss due to disaster          Recover Time Objective (RTO): Maximum amount of time required to recover an application
High availability system will be build with proper redundancy.  In the cloud, multi-AZ and multi-region hosting will help to ensure high availability.	A proper disaster recovery strategy will help to recover quickly from a DDoS attack, pandemic-like situation like COVID.

 Any product company needs to plan for high availability and disaster recovery for business continuity. High availability planning protects us from high probability events that occur on a regular basis.  Instance and data storage failure due to software or hardware issues, a web server not responding due to an unexpected issue, a load-induced outage, and so on are all common occurrences; hosting an instance in more than one availability zone or region will help to resolve this issue. 

The disaster recovery process will help to recover from major outages caused by human-made or natural disasters. Creating a backup of data storage in a different data centre and storing a month's worth of data will aid in data recovery in the event of data loss or data corruption, as well as protecting data loss from cyber-attack. Replicating the data storage and environment in a different location will help to recover quickly from complete environmental failure, but this will not be helpful for data loss or corruption issues.

Over all, High Availability and Disaster Recovery are aimed at the same problem: keeping systems up and running in an operational state, with the main difference being that HA is intended to handle problems while a system is running, while DR is intended to handle problems after a system fails.