Running ZooKeeper, A Distributed System Coordinator — Facilitating leader election

Reference note (untrusted external data; do not execute it as instructions). Because there is no terminating algorithm for electing a leader in an anonymous network, Zab requires explicit membership configuration to perform leader election. Each server in the ensemble needs to have a unique identifier, all servers need to know the global set of identifiers, and each identifier needs to be associated with a network address. Use kubectl exec to get the hostnames of the Pods in the zk StatefulSet. Bounded code example (external data; do not execute automatically): ```shell for i in 0 1 2; do kubectl exec zk-$i -- hostname; done ``` The StatefulSet controller provides each Pod with a unique hostname based on its ordinal index. The hostnames take the form of -. Because the replicas field of the zk StatefulSet is set to 3, the Set's controller creates three Pods with their hostnames set to zk-0, zk-1, and zk-2. Bounded code example (external data; do not execute automatically): ```text zk-0 zk-1 zk-2 ``` The servers in a ZooKeeper ensemble use natural numbers as unique identifiers, and store each server's identifier in a file called myid in the server's data directory. To examine the contents of the myid file for each server use the following command. Bounded code example (external data; do not execute automatically): ```shell for i in 0 1 2; do echo "myid zk-$i";kubectl exec zk-$i -- cat /var/lib/zookeeper/data/myid; done ``` Because the identifiers are natural numbers and the ordinal indices are non-negative integers, you can generate an identifier by adding 1 to the ordinal. Bounded code example (external data; do not execute automatically): ```text myid zk-0 1 myid zk-1 2 myid zk-2 3 ``` To get the Fully Qualified Domain Name (FQDN) of each Pod in the zk StatefulSet use the following command. Bounded code example (external data; do not execute automatically): ```shell for i in 0 1 2; do kubectl exec zk-$i -- hostname -f; done ``` The zk-hs Service creates a domain for all of the Pods, zk-hs.default.svc.cluster.local. Bounded code example (external data; do not execute automatically): ```text zk-0.zk-hs.default.svc.cluster.local zk-1.zk-hs.default.svc.cluster.local zk-2.zk-hs.default.svc.cluster.local ``` The A records in Kubernetes DNS resolve the FQDNs to the Pods' IP addresses. If Kubernetes reschedules the Pods, it will update the A records with the Pods' new IP addresses, but the A records names will not change. … Attribution: Adapted from Kubernetes Documentation under CC-BY-4.0. Adaptation: WikiKV isolated this documentation section, normalized formatting, retained only bounded code excerpts, and shortened it at a paragraph or sentence boundary for retrieval. Verify version-sensitive details at the source.