Which protocol is used for node communication in Cassandra?

The Gossip Protocol is the correct choice for node communication in Cassandra because it is specifically designed to facilitate the communication between nodes in a distributed system. Cassandra employs this protocol to share information about node state, including their availability and other metadata, in a decentralized manner. This characteristic allows each node to disseminate information to become aware of the status of other nodes in the cluster without relying on a central coordinator.

The Gossip Protocol operates effectively in environments where nodes can fail or be added dynamically, as it helps maintain cluster integrity and ensures that the nodes can reach consensus on their state. Each node periodically sends and receives gossip messages, thus updating its view of the cluster. This decentralized and robust approach makes it particularly suitable for Cassandra's architecture, which is designed for high availability and scalability.

In contrast, while TCP/IP is an underlying network protocol that facilitates data transmission, it does not dictate how nodes communicate regarding state information. HTTP/2 and MQTT are protocols used primarily for client-server communication and IoT applications, respectively, but they do not play a role in the internal communication mechanisms of Cassandra nodes. Therefore, the Gossip Protocol is essential for ensuring that nodes work together effectively and maintain the overall health and performance of the Cassandra cluster.