Haproxy 1.6 DNS client issue - Configuration file

resolvers-test.conf

global
  #stats socket /var/run/admin.sock mode 660 level admin
  #stats timeout 30s

defaults
  mode http
  timeout http-keep-alive 10000
  timeout http-request 6s
  timeout connect 7s
  timeout client 10s
  timeout server 10s
  timeout queue 30s
  timeout check 5s

resolvers mydns
  # google will not include any records in truncated replies
  nameserver google 8.8.8.8:53
  # other servers include partial records
  # nameserver public 195.37.58.18:53
  resolve_retries 3
  timeout retry 1s
  hold valid 30s

frontend f_dns_test_http
  bind *:80
  mode http
  default_backend b_dns_test_http

backend b_dns_test_http
  mode http

  server a.glcdn.co a.glcdn.co:80 check resolvers mydns
  server ad.madvertise.de ad.madvertise.de:80 check resolvers mydns
  server apps.buzzcity.net apps.buzzcity.net:80 check resolvers mydns
  server ads.mobgold.com ads.mobgold.com:80 check resolvers mydns
  server android.bcfads.com android.bcfads.com:80 check resolvers mydns
  server req.appads.com req.appads.com:80 check resolvers mydns
  server show.buzzcity.net show.buzzcity.net:80 check resolvers mydns
  server api.analytics.omgpop.com api.analytics.omgpop.com:80 check resolvers mydns
  server r.edge.inmobicdn.net r.edge.inmobicdn.net:80 check resolvers mydns
  server www.mmnetwork.mobi www.mmnetwork.mobi:80 check resolvers mydns
  server img.ads.huntmad.com img.ads.huntmad.com:80 check resolvers mydns
  server creative1cdn.mobfox.com creative1cdn.mobfox.com:80 check resolvers mydns
  server admicro2.vcmedia.vn admicro2.vcmedia.vn:80 check resolvers mydns
  server admicro1.vcmedia.vn admicro1.vcmedia.vn:80 check resolvers mydns
  server s3.phluant.com s3.phluant.com:80 check resolvers mydns
  server c.vrvm.com c.vrvm.com:80 check resolvers mydns
  server go.vrvm.com go.vrvm.com:80 check resolvers mydns
  server static.estebull.com static.estebull.com:80 check resolvers mydns
  server mobile.Banzai.it mobile.Banzai.it:80 check resolvers mydns
  server ads.xxxad.net ads.xxxad.net:80 check resolvers mydns
  server img.ads.mojiva.com img.ads.mojiva.com:80 check resolvers mydns
  server adcontent.saymedia.com adcontent.saymedia.com:80 check resolvers mydns
  server ads.saymedia.com ads.saymedia.com:80 check resolvers mydns
  server ftpcontent.worldnow.com ftpcontent.worldnow.com:80 check resolvers mydns
  server s0.2mdn.net s0.2mdn.net:80 check resolvers mydns
  server img.ads.mocean.mobi img.ads.mocean.mobi:80 check resolvers mydns
  server bigmobileads.com bigmobileads.com:80 check resolvers mydns
  server banners.bigmobileads.com banners.bigmobileads.com:80 check resolvers mydns
  server ads.mopub.com ads.mopub.com:80 check resolvers mydns
  server images.mpression.net images.mpression.net:80 check resolvers mydns
  server images.millennialmedia.com images.millennialmedia.com:80 check resolvers mydns
  server oasc04012.247realmedia.com oasc04012.247realmedia.com:80 check resolvers mydns
  server assets.cntdy.mobi assets.cntdy.mobi:80 check resolvers mydns resolve-prefer ipv4
  server ad.leadboltapps.net ad.leadboltapps.net:80 check resolvers mydns
  server api.airpush.com api.airpush.com:80 check resolvers mydns
  server ad.where.com ad.where.com:80 check resolvers mydns
  server i.tapit.com i.tapit.com:80 check resolvers mydns
  server cdn1.crispadvertising.com cdn1.crispadvertising.com:80 check resolvers mydns
  server cdn2.crispadvertising.com cdn2.crispadvertising.com:80 check resolvers mydns
  server api.yp.com api.yp.com:80 check resolvers mydns
  server ibm.com ibm.com:80 check resolvers mydns resolve-prefer ipv4
  server mailchimp.com mailchimp.com:80 check resolvers mydns
  server do-not-tracker.org do-not-tracker.org:80 check resolvers mydns