Aleksandr Kovalenko created AMBARI-12787:
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             Summary: Add Host is only performing Hostname Resolution check for 
added hosts
                 Key: AMBARI-12787
                 URL: https://issues.apache.org/jira/browse/AMBARI-12787
             Project: Ambari
          Issue Type: Bug
          Components: ambari-web
    Affects Versions: 2.1.0
            Reporter: Aleksandr Kovalenko
            Assignee: Aleksandr Kovalenko
            Priority: Critical
             Fix For: 2.1.2


When hosts are added to the cluster, on Add Host, a Hostname Resolution check 
is performed. This checks on each host that the other hosts are resolving. For 
example, if you have Host1, Host2 and Host3. On each host, Ambari confirms 
Host1, Host2 and Host3 can resolve (by doing this).

{code}
socket.gethostbyname(host) 
{code}

When adding hosts to a cluster via Add Host, Ambari performs the Hostname 
Resolution check but the list of hosts ONLY includes all added hosts, not any 
of the hosts already in the cluster. For example, if I add Host4 and Host5 to 
the cluster, Ambari will check that each of those hosts can resolve Host4 and 
Host5 but not Host1, Host2 or Host3. This can present a problem if these new 
hosts Host 4 and Host5 network is mis-configured. They might not be able to 
resolve the existing cluster hosts and therefore, once we get components 
installed and started, those components might not function in the cluster 
correctly. This can become a challenge to diagnose.

Attaching a few screen shots showing what is happening. c6401 + c6402 are part 
of original cluster and both are passed with the host check. But when I add 
c6403, it doesn't include the existing hosts c6401/c6402 in the check.

The solution is to include existing hosts in the list of hosts to check 
resolution. Understandably, this list might be large in a very big cluster, so 
an option is to ONLY include the set of hosts that include a Master Component 
(like NameNode, etc). 



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