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amazon web services - DNS Round Robin very slow requests in failover scenario -
currently i'm configuring server pool aws. simple setup 2 database servers scalable server array , 2 load balancers in front of all. every machine has failover standing , should pretty robust.
the load balancers should able failover through round robin dns. in happy day scenario both machines hit , distribute traffic on array. when 1 of these machines down round robin dns in combination client browser retry should make browsers should shift target host machine still once hit timeout. not came seems solution.
the problem i'm experiencing following. shift happen not once failed request each , every subsequent request same browser. simple page request takes 21 seconds load after images take 21 seconds load. following page request takes long. failover works same time useless.
output dig:
; <<>> dig 9.6.1-p2 <<>> example.com
;; global options: +cmd
;; got answer:
;; ->>header<<- opcode: query, status: noerror, id: 45224
;; flags: qr rd ra; query: 1, answer: 2, authority: 0, additional: 0
;; question section:
;example.com. in
;; answer section:
www.example.com. 86400 in 1.2.3.4
www.example.com. 86400 in 1.2.3.4
;; query time: 31 msec
;; server: 172.16.0.23#53(172.16.0.23)
;; when: mon dec 20 12:21:25 2010
;; msg size rcvd: 67
thanks in advance!
maarten hoekstra
kingsquare information services
when dns server gives list of ip addresses client, list ordered (possibly in rotating manner, i.e. subsequent dns might return them in different order). browser caches dns response, i.e. list received. not assume failed connection means server down, retry list in same order every time.
so round-robin dns load balancing @ best; not suited support fault tolerance.
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