Avoiding Domain Name System (DNS) problems

Important

To avoid difficulties in using nameservers, you should be aware of the following:
  • Lookups for dynamic names should not be cached. If you use a client that caches nameserver lookup results you cannot be certain that you continue to work with the correct IP address. This might result in the client continuously attempting to call a server region that has been closed, rather than obtaining the address of another server region that has taken over the role previously fulfilled by the other server.
  • A problem can arise due to stress on the nameserver being used. Some lookups succeed, others fail with a NameNotFoundException.
    When the number of concurrent lookups becomes high, perhaps when a client or bean does repeated lookups without caching, the likelihood of encountering one of these nameserver “blips” increases. Possible measures to consider are:
    • Install a machine of higher capacity to run the name server.
    • Code your applications to recognize this possibility and to retry when this error is encountered.
    • Setup the MVS system so that the most commonly used addresses are included in its /etc/hosts file. This bypasses the nameserver lookup for these names and simply uses the address coded in the file.
    • Rather than specify IP addresses by name, specify them by number. (However, this solution is not advisable in a production environment.)