# On a backend server restart, it always gives 503 error
**URL:** https://discourse.haproxy.org/t/on-a-backend-server-restart-it-always-gives-503-error/5726
**Category:** Help!
**Created:** [September 17, 2020, 12:23pm UTC](https://discourse.haproxy.org/t/on-a-backend-server-restart-it-always-gives-503-error/5726 "2020-09-17T12:23:09Z")
**Posts on this page:** 5
**Page:** 1
### Author:  [@tridevk](https://discourse.haproxy.org/u/tridevk)
#### Post date: [September 17, 2020, 12:23pm UTC](https://discourse.haproxy.org/t/on-a-backend-server-restart-it-always-gives-503-error/5726/1 "2020-09-17T12:23:09Z")
Hi,
I have set up where there are multiple back end servers. On restart of any backend server, on accessing the page , it gives 503 error as below:-
===========
# 503 Service Unavailable
# No server is available to handle this request.
On haproxy restart it works once again. This does not seem to be an appropriate behavior. I would like to know how HAProxy keeps track of the backend servers. on restart of backend server, how it will know if the service has become up.
Can anybody kindly help?
regards
tridev
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### Author:  [@jerome](https://discourse.haproxy.org/u/jerome)
#### Post date: [September 17, 2020, 1:26pm UTC](https://discourse.haproxy.org/t/on-a-backend-server-restart-it-always-gives-503-error/5726/2 "2020-09-17T13:26:00Z")
Hi,
It’s hard to help without some configuration shared. Can you please provide the configuration for an affected backend?
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### Author:  [@tridevk](https://discourse.haproxy.org/u/tridevk)
#### Post date: [September 17, 2020, 1:41pm UTC](https://discourse.haproxy.org/t/on-a-backend-server-restart-it-always-gives-503-error/5726/3 "2020-09-17T13:41:29Z")
Hello Jerome,
Thanks for responding.
Following is my haproxy.cfg. I have tried to restart backend “otntomcat” and “ntsm\_serv” and it gives the same problem with both.
Request your help.
thanks
Tridev
global
log stdout format raw local0 debug
defaults
mode http
log global
option http-server-close
option httplog
option dontlognull
option redispatch
option forwardfor
retries 3
backlog 4096
timeout client 20s
timeout client-fin 20s
timeout connect 5s
timeout server 20s
timeout tunnel 15m
timeout http-keep-alive 30s
timeout http-request 10s
timeout queue 5s
timeout tarpit 60s
default-server inter 3s rise 2 fall 3
frontend web\_gateway
bind \*:7777 ssl crt /usr/local/etc/haproxy/cert.crt
log 127.0.0.1 local0 debug
redirect scheme https if !{ ssl\_fc }
http-request add-header X-Forwarded-Proto https
http-request set-query %[query,regsub(:7777,g)]
http-request set-uri %[url,regsub(otntomcat,"$ipv4addr",g)]
acl otntomcat\_path path\_beg -i /oms1350
acl dojoroot\_path path\_beg -i /dojoroot
acl p1 path\_beg -i /jointroot
acl p2 path\_beg -i /jquery
acl p3 path\_beg -i /lodash
acl p4 path\_beg -i /openlayersroot
acl p5 path\_beg -i /search
acl p6 path\_beg -i /svgutilsroot
acl p7 path\_beg -i /d3root
acl p8 path\_beg -i /backbone
acl p9 path\_beg -i /Cpb
use\_backend otntomcat if otntomcat\_path || dojoroot\_path || p1 || p2 || p3 || p4 || p5 || p6 || p7 || p8 || p9
acl cas\_path path\_beg -i /cas
acl session\_path path\_beg -i /session-manager
use\_backend nspos\_serv if cas\_path || session\_path
acl fault\_path path\_beg -i /FaultManagement
use\_backend nspos\_serv1 if fault\_path
acl int\_path path\_beg -i /internal
use\_backend nspos\_serv if int\_path
acl ntsm\_path path\_beg -i /ntsm
use\_backend ntsm\_serv if ntsm\_path
acl systemmonitor\_path path\_beg -i /systemmonitor
use\_backend systemmonitor\_serv if systemmonitor\_path
default\_backend nspos\_serv
backend otntomcat
mode http
balance roundrobin
log stdout local0 debug
server serv01 otntomcat:8443 check ssl verify none
http-response replace-header Location (._)(\botntomcat\b)(._)$ \1"ipv4addr"\3 http-response replace-header Location (.\*)(\b443\b)(.\*) \17777\3
http-response replace-header Location (._)(\b8544\b)(._) \17777\3 http-response replace-header Location (.\*)(\b8545\b)(.\*) \17777\3
http-response replace-header Location (._)(\b8443\b)(._)$ \17777\3
http-response replace-header Location (._)(\b/oms1350/pages/otn\b)(._) \1:7777/oms1350/pages/otn\3
http-request add-header X-Forwarded-Proto https if { ssl\_fc }
backend nspos\_serv
mode http
balance roundrobin
log stdout local0 debug
acl p1 path\_beg -i /session-manager
acl p2 path\_beg -i /cas
acl p3 path\_beg -i /oms1350
acl c1 hdr(Location) urlp(service)
server srv01 nspos:443 check ssl verify none
http-response replace-header Location (._)(\botntomcat\b)(._)$ \1"ipv4addr"\3 http-response replace-header Location (.\*)(\b\/cas\/login\b)(.\*) \1:7777\/cas\/login\3 http-response replace-header Location (.\*)(\b\/oms1350\/login\b)(.\*) \1:7777\/oms1350\/login\3 http-response replace-header Location (.\*)(\b\/session-manager\/login\b)(.\*) \1:7777\/session-manager\/login\3 http-response replace-header Location (.\*)(\b:7777:7777\/session-manager\/login\b)(.\*) \1:7777\/session-manager\/login\3 http-response replace-header Location (.\*)(\b8443\b)(.\*) \17777\3
http-response replace-header Location (._)(\b/cas/logout\b)(._) \1:7777/cas/logout\3
http-request add-header X-Forwarded-Proto https if { ssl\_fc }
backend nspos\_serv1
mode http
balance roundrobin
log 127.0.0.1 local0 debug
server srv01 nspos:8544 check ssl verify none
http-response replace-header Location (._)(\b8544\b)(._)$ \17777\3
http-request add-header X-Forwarded-Proto https if { ssl\_fc }
backend ntsm\_serv
mode http
balance roundrobin
log stdout local0 debug
server srv01 ntsm:8546 check ssl verify none
http-response replace-header Location (._)(\b8546\b)(._)$ \17777\3
http-request add-header X-Forwarded-Proto https if { ssl\_fc }
backend systemmonitor\_serv
mode http
balance roundrobin
log stdout local0 debug
server srv01 mnc-admin:8547 check ssl verify none
http-response replace-header Location (._)(\b8547\b)(._) \17777\3 http-response replace-header Location (.\*)(\b8548\b)(.\*) \17777\3
http-request add-header X-Forwarded-Proto https if { ssl\_fc }
listen stats
bind \*:1974
stats enable
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### Author:  [@jerome](https://discourse.haproxy.org/u/jerome)
#### Post date: [September 17, 2020, 1:48pm UTC](https://discourse.haproxy.org/t/on-a-backend-server-restart-it-always-gives-503-error/5726/4 "2020-09-17T13:48:32Z")
if you use names for server addresses on your server lines, and the IP address associated to the name changes, haproxy can’t know until you restart it if you don’t use a [resolvers](https://cbonte.github.io/haproxy-dconv/2.2/configuration.html#5.3.2) section as detailed [here](https://cbonte.github.io/haproxy-dconv/2.2/configuration.html#5.3)
I’m guessing that’s what happens here since you fix it with an haproxy restart.
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### Author:  [@tridevk](https://discourse.haproxy.org/u/tridevk)
#### Post date: [September 18, 2020, 8:57am UTC](https://discourse.haproxy.org/t/on-a-backend-server-restart-it-always-gives-503-error/5726/5 "2020-09-18T08:57:07Z")
Thank You very much.
after adding a resolver section it started working. appreciate your support.
regards
Tridev