[dnsdist] dnsdist[29321]: Marking downstream IP:53 as 'down'

Wed Mar 23 21:01:40 UTC 2022

Hi,
Thanks for reply...!

We have configured setMaxUDPOutstanding(65535) and still we are seeing backend down, logs are showing frequently as below.

Timeout while waiting for the health check response from backend 192.168.1.1:53
Timeout while waiting for the health check response from backend 192.168.1.2:53

Please have a look at below dnsdist configuration and help us to find misconfiguration (16 Listeners & 8+8 backends added as per vCPUs available (2 Socket x 8 Cores):

controlSocket('127.0.0.1:5199')
setKey("")

---- Listen addresses
addLocal('192.168.0.1:53', { reusePort=true })
addLocal('192.168.0.1:53', { reusePort=true })
addLocal('192.168.0.1:53', { reusePort=true })
addLocal('192.168.0.1:53', { reusePort=true })
addLocal('192.168.0.1:53', { reusePort=true })
addLocal('192.168.0.1:53', { reusePort=true })
addLocal('192.168.0.1:53', { reusePort=true })
addLocal('192.168.0.1:53', { reusePort=true })
addLocal('192.168.0.1:53', { reusePort=true })
addLocal('192.168.0.1:53', { reusePort=true })
addLocal('192.168.0.1:53', { reusePort=true })
addLocal('192.168.0.1:53', { reusePort=true })
addLocal('192.168.0.1:53', { reusePort=true })
addLocal('192.168.0.1:53', { reusePort=true })
addLocal('192.168.0.1:53', { reusePort=true })
addLocal('192.168.0.1:53', { reusePort=true })

---- Back-end server
newServer({address='192.168.1.1', maxCheckFailures=3, checkInterval=5, weight=4, qps=40000, order=1})
newServer({address='192.168.1.1', maxCheckFailures=3, checkInterval=5, weight=4, qps=40000, order=2})
newServer({address='192.168.1.1', maxCheckFailures=3, checkInterval=5, weight=4, qps=40000, order=3})
newServer({address='192.168.1.1', maxCheckFailures=3, checkInterval=5, weight=4, qps=40000, order=4})
newServer({address='192.168.1.1', maxCheckFailures=3, checkInterval=5, weight=4, qps=40000, order=5})
newServer({address='192.168.1.1', maxCheckFailures=3, checkInterval=5, weight=4, qps=40000, order=6})
newServer({address='192.168.1.1', maxCheckFailures=3, checkInterval=5, weight=4, qps=40000, order=7})
newServer({address='192.168.1.1', maxCheckFailures=3, checkInterval=5, weight=4, qps=40000, order=8})
newServer({address='192.168.1.2', maxCheckFailures=3, checkInterval=5, weight=4, qps=40000, order=9})
newServer({address='192.168.1.2', maxCheckFailures=3, checkInterval=5, weight=4, qps=40000, order=10})
newServer({address='192.168.1.2', maxCheckFailures=3, checkInterval=5, weight=4, qps=40000, order=11})
newServer({address='192.168.1.2', maxCheckFailures=3, checkInterval=5, weight=4, qps=40000, order=12})
newServer({address='192.168.1.2', maxCheckFailures=3, checkInterval=5, weight=4, qps=40000, order=13})
newServer({address='192.168.1.2', maxCheckFailures=3, checkInterval=5, weight=4, qps=40000, order=14})
newServer({address='192.168.1.2', maxCheckFailures=3, checkInterval=5, weight=4, qps=40000, order=15})
newServer({address='192.168.1.2', maxCheckFailures=3, checkInterval=5, weight=4, qps=40000, order=16})

setMaxUDPOutstanding(65535)

---- Server Load Balancing Policy
setServerPolicy(leastOutstanding)

---- Web-server
webserver('192.168.0.1:8083')
setWebserverConfig({acl='192.168.0.0/24', password='Secret'})

---- Customers Policy
customerACLs={'192.168.1.0/24'}
setACL(customerACLs)

pc = newPacketCache(300000, {maxTTL=86400, minTTL=0,
temporaryFailureTTL=60, staleTTL=60, dontAge=false})
getPool(""):setCache(pc)

setVerboseHealthChecks(true)

Servers Specs are as below:
Dnsdist LB Server Specs: 16 vCPUs, 16 GB RAM, Virtio NIC (10G) with 16 Multiqueues.
Backend bind9 servers Specs: 16 vCPUs, 16GM RAM, Virtio NIC (10G) with 16 Multiqueues. 

We are trying to handle 500K qps (will increase hardware specs, If required) or with above specs atleast 100K qps.

Regards,
Rais 

-----Original Message-----
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Today's Topics:

   1. dnsdist[29321]: Marking downstream IP:53 as 'down' (Rais Ahmed)
   2. Re: dnsdist[29321]: Marking downstream IP:53 as 'down'
      (Remi Gacogne)

----------------------------------------------------------------------

Message: 1
Date: Tue, 22 Mar 2022 23:00:25 +0000
From: Rais Ahmed <rais.ahmed at tes.com.pk>
To: "dnsdist at mailman.powerdns.com" <dnsdist at mailman.powerdns.com>
Subject: [dnsdist] dnsdist[29321]: Marking downstream IP:53 as 'down'
Message-ID:
	<PAXPR08MB70737E4E1CCEFC4A7F61E1E6A0179 at PAXPR08MB7073.eurprd08.prod.outlook.com>

Content-Type: text/plain; charset="us-ascii"

Hi,

We have configured dnsdist instance to handle around 500k QPS, but we are seeing downstream down frequently once QPS reached above 25k. below are the logs which we found to relative issue.

dnsdist[29321]: Marking downstream server1 IP:53 as 'down'
dnsdist[29321]: Marking downstream server2 IP:53 as 'down'
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Message: 2
Date: Wed, 23 Mar 2022 10:32:22 +0100
From: Remi Gacogne <remi.gacogne at powerdns.com>
To: Rais Ahmed <rais.ahmed at tes.com.pk>, "dnsdist at mailman.powerdns.com"
	<dnsdist at mailman.powerdns.com>
Subject: Re: [dnsdist] dnsdist[29321]: Marking downstream IP:53 as
	'down'
Message-ID: <5a95cbeb-7c82-9bc1-0b4c-8726f814432e at powerdns.com>
Content-Type: text/plain; charset=UTF-8; format=flowed

Hi,

 > We have configured dnsdist instance to handle around 500k QPS, but we  > are seeing downstream down frequently once QPS reached above 25k. below  > are the logs which we found to relative issue.
 >
 > dnsdist[29321]: Marking downstream server1 IP:53 as 'down'
 >
 > dnsdist[29321]: Marking downstream server2 IP:53 as 'down'

You might be able to get more information about why the health-checks are failing by adding setVerboseHealthChecks(true) to your configuration.

It usually happens because the backend is overwhelmed and needs to be tuned to handle the load, but it might also be caused by a network issue, like a link reaching its maximum capacity, or by dnsdist itself being overwhelmed and needing tuning (like increasing the number of
newServer() directives, see [1]).

[1]: 
https://dnsdist.org/advanced/tuning.html#udp-and-incoming-dns-over-https

Best regards,
--
Remi Gacogne
PowerDNS.COM BV - https://www.powerdns.com/

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