Redis vs etcd: What are the differences?

Redis and etcd are two popular distributed key-value stores. Let's explore the key differences between the two:

1. Data Model: Redis follows a simple key-value model where the value can be a wide range of data structures like strings, lists, sets, etc. On the other hand, etcd provides a distributed key-value model with very limited data structures, primarily focusing on managing configurations and coordinating distributed systems.

2. Consistency Guarantees: Redis provides eventual consistency, meaning that updates to the data are not immediately reflected across all instances but eventually propagate. In contrast, etcd offers strong consistency, ensuring that all nodes see the same set of data at any given time.

3. Scaling: Redis supports horizontal scaling via replication and sharding. It allows for the distribution of data across multiple nodes, improving performance and capacity. Etcd also supports replication and clustering but lacks built-in sharding capability, limiting its scalability compared to Redis.

4. Data Persistence: Redis offers different persistence options, including both snapshotting and append-only file (AOF) persistence. It allows data to survive restarts or power failures. Etcd, on the other hand, stores data primarily in memory, with an option for periodic snapshots. It is not designed for long-term data persistence and focuses more on real-time coordination.

5. Cluster Management: Redis does not provide built-in cluster management. It relies on external tools like Redis Cluster or Redis Sentinel for managing distributed deployments. Etcd, being designed as a distributed systems coordination tool, provides built-in cluster management with fault tolerance and leader election capabilities.

6. APIs and Language Support: Redis offers a rich set of APIs and supports multiple programming languages, making it easy to integrate into various applications. Etcd primarily exposes a simple HTTP(S) API and provides official clients for popular languages like Go, Python, and Java.

In summary, Redis focuses on providing a versatile key-value store and etcd specializes in coordinating distributed systems and managing configurations.