DNS Entry Record Types

Question

When using a DNS entry to configure your ArcGIS Enterprise installation, does the record need to be an A record or a CNAME record?  In other words, should it map a domain name to the host name or to an IP address?  I'm seeing smatterings that point to CNAME but I want to confirm.

Thanks,

Nathan

MingLee · Answer

Just adding to what Scott said - the DNS record type is partly dependent on what you've been given.

The A and CNAME records are the two common ways to map a host name (“name”) to one or more IP addresses. There are important differences between these two records.

An A record points a DNS name to a specific IP. If you want FQDN maps.mingworld.net to point to your server or load balancer with the following external IP of 99.12.12.187 you’ll configure:

maps.mingworld.net. A 99.12.12.187

A CNAME record points a name to another name instead of to an IP. The CNAME source represents an alias and is common with most of the Public Cloud Providers where your deployed server is accessible through this alias rather than a fixed IP as your provider most likely will recycle their pool of IPs.

For example: mingworld.uksouth.cloudapp.com would be configured as a CNAME thus:

maps.mingworld.net. CNAME mingworld.uksouth.cloudapp.com.

In each case, typing in maps.mingworld.net will resolve (and redirect) to either the IP or the CNAME seamlessly.

As for A records being a bit more efficient; that it is probably because there is a less involved process of resolving access to the resource. A CNAME ultimately, also needed to resolve to an IP (and then MAC address etc.)

Scott_Tansley · Answer

For the URL that your users use, e.g. maps.domain.com, you'll almost certainly use a CNAME.

If you're using internal load balancers (for example) then you can use a CNAME or A Record.  Personally, I've seen a lot of warnings in the portal/server logs resulting from a CNAME.  When I've encouraged the client to use an A Record, the warnings have disappeared.  It's not standard practice to use A records (other than for the host name) but it works better in my opinion