DNS Resolution *Sigh* v1.7.1


#1

Hey all,

I seem to be seeing unexpected behaviour using dynamic DNS resolution - any help or advice you can offer would be much appreciated.

I keep seeing messages like this in the log:

Server backend_name/server_name is going DOWN for maintenance (DNS timeout status). 0 active and 0 backup servers left. 0 sessions active, 0 requeued, 0 remaining in queue.

Running a tcpdump on the DNS queries haproxy generates, I typically see successful DNS responses less than 3 seconds before seeing this error. Often I will see this message 3s before the one above (even with a hold valid value of 30s), I also see it when the server is apparently marked as DOWN:

backend_name/server_name changed its IP from 10.xx.xx.xx to 10.xx.xx.xx by name-dns/name-dns-01

I also often see this message even if the server hasn’t been reported as down:

Server backend_name/server_name administratively READY thanks to valid DNS answer.

DNS responses typically arrive in under 30ms.

The show stat resolvers command does not show that any timeouts occurred:

  sent: 10797
  valid: 1034
  update: 493
  cname: 0
  cname_error: 0
  any_err: 869
  nx: 0
  timeout: 0
  refused: 0
  other: 0
  invalid: 0
  too_big: 0
  truncated: 0
  outdated: 260

#2

Interestingly, when I switch to a single process (from 4) the problem does not occur. Additionally, no IPv6 DNS requests are made.

Also, a DNS request is not made with every health check (set to 10s), instead it’s made every 30s, which is what I have hold valid configured for.


#3

It’s a bug, it was reported on the mailing list as well:
https://www.mail-archive.com/haproxy@formilux.org/msg24272.html

I’m gonna poke the ML thread, lets see if we can get this fixed.


#4

Guys,

Sorry I missed the mail speaking about the bug in the ML.
I’m going to have a look at it over the WE and come back to you asap next week.

Baptiste


#5

Many thanks @lukastribus, I think I’ll get subscribed to the list so I can follow these things.

Thanks also @Baptiste, appreciated.

As ever, kudos to the whole team for an amazing product,


#6

Hi,

I just sent a patch to the ML to fix this issue.
Please check:
https://www.mail-archive.com/haproxy@formilux.org/msg24795.html

Baptiste


#7

Hey,

Thanks Baptiste, I’m following along on the mailing list.