Zookeeper

Zookeeper’s API is essentially a hierarchical namespace similar to a filesystem.

Chubby also provides a hierarchical namespace, while etcd provides a key-value interface.

In the illustration below, we can see:

• Every name is a sequence of path elements separated by a slash (/).
• Every name represents a data node (called znode), which can contain a piece of metadata and children nodes.

For example, the node “/a/b” is considered a child of the node “/a”.