How To Configure Exalogic NM2-GW Switches To Be DNS Clients of a DNS Server accessible over the EoIB network (Doc ID 1669990.1)

Last updated on JUNE 13, 2017

Applies to:

Oracle Exalogic Elastic Cloud Software - Version 2.0.6.0.0 and later
Information in this document applies to any platform.

Goal

Under certain limited circumstances, it may be desirable to configure each of the NM2-GW switches in an Exalogic Physical or Virtual environment to use a remote DNS server, accessible over the EoIB network for hostname resolution. This support note illustrates the steps that can be followed to achieve such a configuration.

Limitations/Important Considerations

NOTE:
  • As the NM2-GW switches have very less need to connect to other hosts, there is less benefit configuring the switches to allow DNSresolution of named hosts.
    • One possible exception to this would be to support the use of a hostname in the NTP configuration file (/etc/ntp.conf), so the NTP configuration on each NM2-GW switch may exactly match the NTP configuration supplied on compute nodes, where DNS is available and hostnames rather than IP addresses can be used.

  • Currently, since the Exalogic Exachk utility (see: <NOTE:1449226.1> - Exachk Health-Check Tool for Exalogic) validates that the NTP configuration is consistent across all components, it can flag warnings that the NTP configuration on NM2-GW switches (which might be using IP addresses) is inconsistent with the configuration on other components (where hostname values may be used), despite the fact that the configurations are logicallyidentical, even though they do not match literally.
    • This warning can be resolved by configuring each of the NM2-GW switches to use a remote DNS server, such that the NTP server locations provided in the /etc/ntp.conf file reference hostnames that are a literal match for the hostnames used within the NTP configuration on other components.
    • The warning can also be resolved by using IP addresses in the NTP configuration for other components, as the lowest common denominator available across all components.

  • However, in the case of an Exalogic Virtual environment, where Enterprise Manager OpsCenter (EMOC) drives commands against the NM2-GW switches on behalf of various end user initiated jobs (e.g. Create vServer, Start vServerDefine Network etc.) introducing an additional dependency on a remote DNS server risks exposing SSH connections made by EMOC Proxy Controllers to failure and additional latency
    • This additional latency can result in delayed completion of tasks executed by EMOC that are subject to timed execution. These may time-out causing EMOC Jobs to fail and rollback at times when the remote DNS server is not accessible or responding promptly.
    • Therefore, unless your NTP server locations change frequently, it is recommended that you do NOT configure your NM2-GW switches to use a remote DNSserver and instead either:
      1. provide NTP server locations via IP addresses across all components (so that all NTP configurations are both logically and literally identical across all Exalogic components)
      2. reference NTP servers by hostnames on other components and by IP addresses on NM2-GW switches but ignore Exachk warnings that the configurations differ (since they are at least logically if not literally identical)
      3. provide NTP server locations via hostnames on the NM2-GW switches but maintain entires in the /etc/hosts file on each NM2-GW switches (this allows these hostnames to be statically resolved to the desired IP address locally, without needing to resolve them dynamically via DNS)

 

Solution

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