An Apache ZooKeeper developer designs, implements, and maintains systems using Apache ZooKeeper, a service for distributed systems offering a hierarchical key-value store, used to provide distributed synchronization. They ensure data consistency across nodes in distributed applications, manage large set of hosts, and facilitate robust messaging amongst them. They handle tasks like system status monitoring, distributed configuration, synchronization, and group services. They troubleshoot ZooKeeper-related issues and optimize its performance. They also collaborate with other developers to integrate ZooKeeper into broader application architectures, while ensuring its high availability and failover capabilities.