PowerDNS CNAME with multiple A records produces unexpected results
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bwight
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Published on 2012-06-29T15:49:26Z
Indexed on
2012/07/01
21:18 UTC
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Hit count: 400
This problem from what i can tell is isolated to PowerDNS. The servers are running two packages pdns-static-3.0.1-1.i386.rpm
and pdns-recursor-3.3-1.i386.rpm
on the most recent version of Amazon Linux.
The amazon ec2 loadbalancers are assigned a CNAME with multiple hosts. Below is an example of the actual behavior. Notice how the hosts are always in the same order.
[root@localhost ~]# host cache.domain.com
cache.domain.com is an alias for xxxxx.us-east-1.elb.amazonaws.com.
xxxxx.us-east-1.elb.amazonaws.com has address aaa.aaa.aaa.aaa
xxxxx.us-east-1.elb.amazonaws.com has address bbb.bbb.bbb.bbb
[root@localhost ~]# host cache.domain.com
cache.domain.com is an alias for xxxxx.us-east-1.elb.amazonaws.com.
xxxxx.us-east-1.elb.amazonaws.com has address aaa.aaa.aaa.aaa
xxxxx.us-east-1.elb.amazonaws.com has address bbb.bbb.bbb.bbb
[root@localhost ~]# host cache.domain.com
cache.domain.com is an alias for xxxxx.us-east-1.elb.amazonaws.com.
xxxxx.us-east-1.elb.amazonaws.com has address aaa.aaa.aaa.aaa
xxxxx.us-east-1.elb.amazonaws.com has address bbb.bbb.bbb.bbb
Expected behavior is round robin for the hosts
[root@localhost ~]# host cache.domain.com
cache.domain.com is an alias for xxxxx.us-east-1.elb.amazonaws.com.
xxxxx.us-east-1.elb.amazonaws.com has address aaa.aaa.aaa.aaa
xxxxx.us-east-1.elb.amazonaws.com has address bbb.bbb.bbb.bbb
[root@localhost ~]# host cache.domain.com
cache.domain.com is an alias for xxxxx.us-east-1.elb.amazonaws.com.
xxxxx.us-east-1.elb.amazonaws.com has address bbb.bbb.bbb.bbb
xxxxx.us-east-1.elb.amazonaws.com has address aaa.aaa.aaa.aaa
[root@localhost ~]# host cache.domain.com
cache.domain.com is an alias for xxxxx.us-east-1.elb.amazonaws.com.
xxxxx.us-east-1.elb.amazonaws.com has address aaa.aaa.aaa.aaa
xxxxx.us-east-1.elb.amazonaws.com has address bbb.bbb.bbb.bbb
The addresses eventually do swap but it seems to be on a 30 minute cache timer changing the TTL of the record doesn't appear to affect anything. It appears as though the resolver has a cache of the response. This adversely affects my application because all of the load is only being sent to one of the loadbalancers (Availability Zones) so if I have servers in two zones then only one zone is under load at a time.
Do you know how I can fix this so that each time the host is resolved the order of the addresses is alternating.
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