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From bugzi...@apache.org
Subject DO NOT REPLY [Bug 42349] New: - DNS round robin solution using CNAME is against RFC
Date Tue, 08 May 2007 05:30:28 GMT
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http://issues.apache.org/bugzilla/show_bug.cgi?id=42349

           Summary: DNS round robin solution using CNAME is against RFC
           Product: Apache httpd-2
           Version: 2.3-HEAD
          Platform: Other
        OS/Version: other
            Status: NEW
          Severity: normal
          Priority: P2
         Component: Documentation
        AssignedTo: bugs@httpd.apache.org
        ReportedBy: apache.org@moto-coda.org


The Load Balancing solution 1 "DNS Round-Robin" as detailed here:

http://httpd.apache.org/docs/2.2/misc/rewriteguide.html

... is against RFC 2181, which states:

===
10.1. CNAME resource records

   The DNS CNAME ("canonical name") record exists to provide the
   canonical name associated with an alias name.  There may be only one
   such canonical name for any one alias.  That name should generally be
   a name that exists elsewhere in the DNS, though there are some rare
   applications for aliases with the accompanying canonical name
   undefined in the DNS.  An alias name (label of a CNAME record) may,
   if DNSSEC is in use, have SIG, NXT, and KEY RRs, but may have no
   other data.  That is, for any label in the DNS (any domain name)
   exactly one of the following is true:

     + one CNAME record exists, optionally accompanied by SIG, NXT, and
       KEY RRs,
     + one or more records exist, none being CNAME records,
     + the name exists, but has no associated RRs of any type,
     + the name does not exist at all.
===

Note the section that says "one" CNAME record, which means "not more than one".

>From what I've been able to determine, there was multiple CNAME support in BIND
4.x, however this was phased out (but still supported) in BIND 8.x, and has been
completely removed from BIND 9.1+. Other name services may or may not support
multiple CNAME records, however it is not a reliable method of load balancing
and should not be given as such in the documentation. At the very least the
documentation should point out that this feature may not (and is unlikely to) be
supported by most DNS systems.

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