What is etcd and why was it chosen as the storage for Kubernetes? What properties does it have?

etcd is a distributed, fault-tolerant key-value store with Raft consensus support. It is used in Kubernetes to store all configuration information and cluster state.

Why choose etcd for Kubernetes:

• Consistency: etcd provides strong data consistency, which is critical for the correct operation of the cluster.
• Fault Tolerance: thanks to the Raft algorithm, data is replicated across multiple nodes, ensuring resilience to failures.
• API simplicity: offers a simple HTTP/JSON API for reading and writing data.
• High performance: optimized for fast read and write operations.

Properties of etcd:

• Distributed and data replication.
• Strong consistency (linearizability).
• Support for watchers to monitor real-time changes.
• Reliable storage with a transaction log (WAL).

Thus, etcd provides Kubernetes with a reliable and consistent storage for managing cluster state.