Zookeeper vs etcd: What are the differences?

Zookeeper and etcd are both distributed systems that provide coordination and naming services for distributed applications. Let's explore the key differences between them.

1. Consistency Model: Zookeeper follows a strong consistency model, ensuring that all clients see the same view of the data at the same time. In contrast, etcd follows a linearizability consistency model, guaranteeing that writes will be seen by all clients in a consistent order.

2. API: Zookeeper primarily provides a simple hierarchical namespace for storing data, similar to a file system. It offers a limited set of operations such as create, read, update, and delete. On the other hand, etcd provides a key-value store with a richer API, supporting additional features like atomic compare-and-swap operations and watches.

3. Ecosystem: Zookeeper has been around for longer and has a mature ecosystem with extensive support and integration in various frameworks and applications. Etcd, although younger, has gained popularity and is widely adopted in the container orchestration platform Kubernetes.

4. Performance: Zookeeper is known for its high throughput and low latency, making it suitable for applications that require fast data updates. Etcd, based on the Raft consensus algorithm, provides comparable performance and is designed to handle large-scale distributed systems.

5. Language Support: Zookeeper is written in Java and provides official client libraries for Java, C, and Python among others. In contrast, etcd is implemented in Go and provides official client libraries for Go, Python, Java, Ruby, and more, offering a broader range of language support.

6. Ease of Deployment: Zookeeper requires manual configuration and setting up a quorum of servers for reliability. Etcd, being part of the Kubernetes ecosystem, benefits from its easy deployment and management capabilities, making it simpler to use in Kubernetes clusters.

In summary, Zookeeper offers strong consistency, a simple API, and a mature ecosystem, while etcd provides linearizability, a rich API, and easy integration with Kubernetes. Both are reliable distributed systems suitable for coordination and naming services in distributed applications.