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 FEBRUARY 25, 2019
Oracle Exalogic Elastic Cloud Software - Version 188.8.131.52.0 and later Information in this document applies to any platform.
Under certain limited circumstances, it may be desirable to configure each of the NM2-GW switches in an Exalogic Physical 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 and Important Considerations for Exalogic Virtual Environments
As the NM2-GW switches have little need to connect to other hosts, there is less benefit configuring the switches to allow DNS resolution 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 logically identical, even though they do not match literally.
In the case of Exalogic Physical environments. this warning can be resolved by configuring each of the NM2-GW switches to use a remote DNS server, such that the NTP server in /etc/ntp.conf file can be provided as hostnames that are a literal match for the hostnames that can be provided within the NTP configuration on other rack components.
However, 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, the configuration provided in this note is *NOT* supported for Exalogic Virtual environments, where Enterprise Manager OpsCenter (EMOC) drives commands against the NM2-GW switches on behalf of end user initiated jobs (e.g. Create vServer, Start vServer, Define Network etc.). In the case of Exalogic Virtual environments the added dependency on a remote DNS server risks exposing SSH connections made by EMOC Proxy Controllers to additional latency that prevents EMOC tasks from completing in the time expected and therefore failing and rolling back.
Therefore, for Exalogic Virtual configurations it is *NOT* supported to configure your NM2-GW switches to use a remote DNS server and instead either:
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)
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)
provide NTP server locations via hostnames on the NM2-GW switches but maintain entries 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)
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