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

• 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
• Assignee: Flavio Paiva Junqueira
• Reporter: Eron Wright
• Created: 19/Feb/18 19:28
• Updated: 31/Dec/19 19:46
• Resolved: 08/May/18 22:57

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.

Issue Links

• relates to: ZOOKEEPER-1506 Re-try DNS hostname -> IP resolution if node connection fails
• links to: GitHub Pull Request #468
• links to: GitHub Pull Request #513