[ZOOKEEPER-2982] Re-try DNS hostname -> IP resolution - ASF JIRA

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Details

Type: Bug
Status: Resolved
Priority: Blocker
Resolution: Fixed
Affects Version/s: 3.5.0, 3.5.1, 3.5.3
Fix Version/s: 3.5.4, 3.6.0
Component/s: server
Labels:
None

Description

~~ZOOKEEPER-1506~~ fixed a DNS resolution issue in 3.4. Some portions of the fix haven't yet been ported to 3.5.

To recap the outstanding problem in 3.5, if a given ZK server is started before all peer addresses are resolvable, that server may cache a negative lookup result and forever fail to resolve the address. For example, deploying ZK 3.5 to Kubernetes using a StatefulSet plus a Service (headless) may fail because the DNS records are created lazily.

2018-02-18 09:11:22,583 [myid:0] - WARN  [QuorumPeer[myid=0](plain=/0:0:0:0:0:0:0:0:2181)(secure=disabled):Follower@95] - Exception when following the leader
java.net.UnknownHostException: zk-2.zk.default.svc.cluster.local
        at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:184)
        at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392)
        at java.net.Socket.connect(Socket.java:589)
        at org.apache.zookeeper.server.quorum.Learner.sockConnect(Learner.java:227)
        at org.apache.zookeeper.server.quorum.Learner.connectToLeader(Learner.java:256)
        at org.apache.zookeeper.server.quorum.Follower.followLeader(Follower.java:76)
        at org.apache.zookeeper.server.quorum.QuorumPeer.run(QuorumPeer.java:1133)

In the above example, the address `zk-2.zk.default.svc.cluster.local` was not resolvable when the server started, but became resolvable shortly thereafter. The server should eventually succeed but doesn't.