Technical data

Using DNS to Balance Work Load
6.2 Round-Robin Scheduling
In the example, the DNS cluster alias is defined as robin . When the DNS server
receives queries for robin , it shuffles the A resource records in a round-robin
manner.
;
; TCP/IP DNS cluster load sharing - round robin method
; DNS cluster alias: "robin"
robin IN A 9.20.208.47
IN A 9.20.208.30
IN A 9.20.208.72
;
birdy IN A 9.20.208.47
seagull IN A 9.20.208.30
owl IN A 9.20.208.72
;
A user enters the TELNET command, specifying the DNS cluster alias ROBIN.
The first query to the DNS name server results in the following TELNET session:
$ TELNET ROBIN
%TELNET-I-TRYING, Trying ... 9.20.208.47
%TELNET-I-SESSION, Session 01, host birdy, port 23
-TELNET-I-ESCAPE, Escape character is ^]
The TELNET client connects to host birdy at IP address 9.20.208.47, the first
resource record in the list.
The second query to the name server results in the following TELNET session:
$ TELNET ROBIN
%TELNET-I-TRYING, Trying ... 9.20.208.30
%TELNET-I-SESSION, Session 01, host seagull, port 23
-TELNET-I-ESCAPE, Escape character is ^]
The TELNET client connects to host seagull at IP address 9.20.208.30, the next
resource record in the list.
The third query to the name server results in the following TELNET session:
$ TELNET ROBIN
%TELNET-I-TRYING, Trying ... 9.20.208.72
%TELNET-I-SESSION, Session 01, host owl, port 23
-TELNET-I-ESCAPE, Escape character is ^]
TELNET connects to host owl at IP address 9.20.208.72, the next resource record
in the list.
The fourth query to the name server results in the following TELNET session:
$ TELNET ROBIN
%TELNET-I-TRYING, Trying ... 9.20.208.47
%TELNET-I-SESSION, Session 01, host birdy, port 23
-TELNET-I-ESCAPE, Escape character is ^]
TELNET again connects to host birdy at IP address 9.20.208.47. This is the start
of the cycle repeating. The cycle repeats for the subsequent queries.
The SHOW HOST display for this DNS name server shows the shuffling effect
in greater detail. Notice that the output displays the cluster alias name for each
host involved in round-robin scheduling.
6–2 Using DNS to Balance Work Load