Introduction NoSQL databases are systems designed to run without interruption of service. Many web-based businesses require data services that are available without interruption. For example, databases that support online purchasing need to be available 24 hours a day, 7 days a week, 365 days a year. Requirements You will research the different strategies used by NoSQL databases to ensure high availability, and write a short report on your findings. Here are the specific requirements: 1. Define what is high availability, and how to measure it. 2. Write a report to explain how a NoSQL database can be highly available. You must use specific examples of existing NoSQL databases in your answer (Identify 5 NoSQL databases. For each, explain the strategies for high availability. 3. The main part of the report should be no more than 600 words. 4. In a bibliography, include the references you used to write the body of the report. 5. Include a proper cover page for the report with: a. The Assignment number and title b. Your name and Student ID c. The due date

High availability is a critical requirement for many web-based businesses, especially those that rely heavily on data services such as online purchasing. NoSQL databases have emerged as popular solutions to address the need for continuous availability of data. In this report, we will delve into the strategies used by NoSQL databases to ensure high availability, with a particular focus on five prominent databases.

To begin, let’s define high availability in the context of databases. High availability refers to the ability of a system to remain accessible and function properly even in the face of failures or other disruptions. It is typically measured by metrics such as uptime percentage, which indicates the percentage of time a system is available for use.

For a NoSQL database to achieve high availability, it must employ a range of strategies. Let’s examine five popular NoSQL databases in terms of their strategies for ensuring high availability:

1. Cassandra: Cassandra is a distributed database that utilizes a peer-to-peer architecture and a replication mechanism called “token ring.” It allows data to be replicated across multiple nodes, ensuring fault tolerance and seamless failover. In the event of a node failure, Cassandra uses hinted handoff and read repair mechanisms to maintain consistency and availability.

2. MongoDB: MongoDB employs a replica set architecture where multiple copies of data, known as replicas, are distributed across different servers. It relies on a primary-secondary model, where one node serves as the primary replica and others act as secondary replicas. The primary replica handles all write operations, while secondary replicas asynchronously replicate data from the primary. In case of primary replica failure, one of the secondary replicas is elected as the new primary, ensuring continuous availability.

3. Apache HBase: HBase follows a master-slave architecture, with one master node coordinating operations and multiple slave nodes storing data. It achieves high availability through automatic failover, where a standby master node takes over if the primary master fails. Data is also replicated across multiple regions to mitigate the risk of data loss.

4. Couchbase: Couchbase utilizes a distributed architecture known as the Couchbase Ring. Data is automatically sharded and replicated across nodes in the ring, allowing for fault tolerance and continuous availability. In the event of a node failure, data is automatically rebalanced across the remaining nodes, ensuring high availability.

5. Amazon DynamoDB: DynamoDB is a fully managed NoSQL database service provided by Amazon Web Services (AWS). It ensures high availability by storing multiple copies of data across different availability zones within a region. The service automatically handles failover and replication, allowing for continuous availability of data.

In conclusion, NoSQL databases employ various strategies to ensure high availability, including replication, fault tolerance mechanisms, automatic failover, and data distribution across multiple nodes. Cassandra, MongoDB, Apache HBase, Couchbase, and Amazon DynamoDB are just a few examples of databases that offer robust high availability features. By employing these strategies, businesses can ensure their data services remain uninterrupted, meeting the demands of a continuously connected world.