Availability

Availability in distributed system design refers to the ability of a distributed system to provide access to its services or resources to its users, even in the presence of failures. In other words, an available system is always ready to respond to requests and provide its services to users, regardless of any faults or failures that may occur in the system.

In the hotel room booking example, the system can be highly available if the writes and reads happen from only one or a quorum of replicas. This ensures that the user requests will be served by fewer nodes and doesn’t require all the nodes to be up. So, in case one or more nodes are in a failed state, the system as a whole is available to take writes and reads.

Achieving high availability in distributed systems can be challenging because distributed systems are composed of multiple components, each of which may be subject to failures such as crashes, network failures, or communication failures.

To ensure...