What is Availability pattern?

Availability patterns refer to the strategies and techniques used to ensure that a system or service is available and can handle requests at all times. High availability is a key requirement for many systems, as it ensures that users can access the system or service whenever they need it.

One example of an availability pattern is the use of load balancers. A load balancer distributes incoming traffic across multiple servers, ensuring that no single server becomes overwhelmed and unavailable. This helps to ensure that the system or service can handle a high volume of requests without becoming unavailable.

Another example is the use of failover systems. A failover system automatically switches to a backup server or system in the event of a failure, ensuring that the system or service remains available even if a primary server or system goes down.

A third example is the use of redundancy. Redundancy is the duplication of critical components of a system or service in order to ensure that they are always available. This can include redundant servers, storage systems, or even power supplies.

Another pattern is the use of replication, where data is duplicated across multiple servers or storage devices, ensuring that if one fails, the others can take over. This can be achieved through a variety of methods, such as master-slave replication, where changes made to the master server are automatically replicated to the slaves, or peer-to-peer replication, where all servers have equal status and changes made to any server are replicated to all others.

A specific example of High Availability is the use of Amazon Web Services (AWS) Elastic Load Balancer (ELB) in conjunction with Auto Scaling Group (ASG) and Amazon Elastic Block Store (EBS) to create a highly available application. The ELB automatically distributes incoming traffic to multiple Amazon Elastic Compute Cloud (EC2) instances in the ASG. If an instance fails or becomes unavailable, the ASG automatically replaces it with a new one, and the ELB automatically starts routing traffic to the new instance. And the EBS ensures that data is stored redundantly across multiple availability zones in the same region, so that it can be recovered in case of physical failure of any one availability zone.

Overall, availability patterns aim to ensure that a system or service is always available to users, even in the face of failures or other disruptions. This can be achieved through a variety of techniques, including load balancing, failover systems, and redundancy.