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https://issues.apache.org/jira/browse/ZOOKEEPER-3723?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]
Mate Szalay-Beko resolved ZOOKEEPER-3723.
-----------------------------------------
Resolution: Fixed
> Zookeeper Client should not fail with ZSYSTEMERROR if DNS does not resolve
> one of the servers in the zk ensemble.
> ------------------------------------------------------------------------------------------------------------------
>
> Key: ZOOKEEPER-3723
> URL: https://issues.apache.org/jira/browse/ZOOKEEPER-3723
> Project: ZooKeeper
> Issue Type: Improvement
> Components: c client, java client
> Affects Versions: 3.5.5
> Reporter: Suhas Dantkale
> Priority: Minor
> Labels: pull-request-available
> Fix For: 3.5.8
>
> Time Spent: 1h 20m
> Remaining Estimate: 0h
>
> This is a minor enhancement request to not fail the session initiation if the
> DNS is not able to resolve the hostname of one of the servers in the
> Zookeeper ensemble.
>
> The Zookeeper client resolves all the hostnames in the ensemble while
> establishing the session.
> In Kubernetes environment with coreDNS, the hostname entry gets removed from
> coreDNS during the POD restarts. Though we can manipulate the coreDNS
> settings to delay the removal of the hostname entry from DNS, we don't want
> to leave any race where Zookeeper clinet is trying to establish a session and
> it fails because the DNS temporarily is not able to resolve the hostname. So
> as long as one of the servers in the ensemble is able to be DNS resolvable,
> should we not fail the session establishment with hard error and instead try
> to establish the connection with one of the other servers?
>
> Look at the below snippet where resolve_hosts() fails with ZSYSTEMERROR.
> {code:java}
> if ((rc = getaddrinfo(host, port_spec, &hints, &res0)) != 0) {
> //bug in getaddrinfo implementation when it returns
> //EAI_BADFLAGS or EAI_ADDRFAMILY with AF_UNSPEC and
> // ai_flags as AI_ADDRCONFIG
> #ifdef AI_ADDRCONFIG
> if ((hints.ai_flags == AI_ADDRCONFIG) &&
> // ZOOKEEPER-1323 EAI_NODATA and EAI_ADDRFAMILY are deprecated in FreeBSD.
> #ifdef EAI_ADDRFAMILY
> ((rc ==EAI_BADFLAGS) || (rc == EAI_ADDRFAMILY))) {
> #else
> (rc == EAI_BADFLAGS)) {
> #endif
> //reset ai_flags to null
> hints.ai_flags = 0;
> //retry getaddrinfo
> rc = getaddrinfo(host, port_spec, &hints, &res0);
> }
> #endif
> if (rc != 0) {
> errno = getaddrinfo_errno(rc);
> #ifdef _WIN32
> LOG_ERROR(LOGCALLBACK(zh), "Win32 message: %s\n",
> gai_strerror(rc));
> #elif __linux__ && __GNUC__
> LOG_ERROR(LOGCALLBACK(zh), "getaddrinfo: %s\n",
> gai_strerror(rc));
> #else
> LOG_ERROR(LOGCALLBACK(zh), "getaddrinfo: %s\n",
> strerror(errno));
> #endif
> rc=ZSYSTEMERROR;
> goto fail;
> }
> }
> {code}
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