ImagePullBackOff means there was a problem pulling a container image required by your Pod. Kubernetes “backs off” before retrying, adding a delay that’s intended to provide time for any temporary issues to resolve themselves

ZooKeeper provides multiple feature for distributed applications. It can manage large set of hosts & complicated process. Distributed configurations managements. Self election/ Consensus building. Coordination and locks. Key value store. Zookeeper used in many distributed systems like Hadoop, Kafka.