haproxy heartbeat with backend based on http post - haproxy

Question

I want to create a configuration such that the heartbeat between haproxy and the backend is based on HTTP POST.
Does anyone have any idea about this?
I have tried the below configuration, but it only sent the http HEAD to the backend server (I want HTTP POST):
backend mlp
mode http
balance roundrobin
server mlp1 192.168.12.165:9210 check
server mlp2 192.168.12.166:9210 check
Thanks for your help.
#Mohsin,
Thank you so much. I indeed work.
But I want to specify the request message, seems my configure doesn't work. I appreciate that if you can help too.
[root#LB_vAPP_1 tmp]# more /var/www/index.txt
POST / HTTP/1.1\r\nHost: 176.16.0.8:2234\r\nContent-Length: 653\r\n\r\n<?xml version=\"1.0\" encoding=\"gb2312\"?>\r\n<svc_init ver=\"3.2.0\">\r\n<hdr ver=\"3.2.0\">\r\n<client>\r\n<id>915948</id>\r\n<pwd>915948</pwd>\r\n<serviceid></serviceid>\r\n</client>\r\n<requestor><id>13969041845</id></requestor>\r\n</hdr>\r\n<slir ver=\"3.2.0\" res_type=\"SYNC\">\r\n<msids><msid enc=\"ASC\" type=\"MSISDN\">00000000000</msid></msids>\r\n<eqop>\r\n<resp_req type=\"LOW_DELAY\"/>\r\n<hor_acc>200</hor_acc>\r\n</eqop>\r\n<geo_info>\r\n<CoordinateReferenceSystem>\r\n<Identifier
>\r\n<code>4326</code>\r\n<codeSpace>EPSG</codeSpace>\r\n<edition>6.1</edition>\r\n</Identifier\r\n</CoordinateReferenceSystem>\r\n</geo_info>\r\n<loc_type type=\"CURRENT_OR_LAST\"/>\r\n<prio type=\"HIGH\"/>\r\n</slir>\r\n</svc_init>\r\n\r\n\r\n\r\n
my haproxy.conf file is as bellowing:
#---------------------------------------------------------------------
# Example configuration for a possible web application. See the
# full configuration options online.
#
# http://haproxy.1wt.eu/download/1.4/doc/configuration.txt
#
#---------------------------------------------------------------------
#---------------------------------------------------------------------
# Global settings
#---------------------------------------------------------------------
global
# to have these messages end up in /var/log/haproxy.log you will
# need to:
#
# 1) configure syslog to accept network log events. This is done
# by adding the '-r' option to the SYSLOGD_OPTIONS in
# /etc/sysconfig/syslog
#
# 2) configure local2 events to go to the /var/log/haproxy.log
# file. A line like the following can be added to
# /etc/sysconfig/syslog
#
# local2.* /var/log/haproxy.log
#
log 127.0.0.1 local7
chroot /var/lib/haproxy
pidfile /var/run/haproxy.pid
ulimit-n 65536
daemon
nbproc 1
# turn on stats unix socket
stats socket /var/lib/haproxy/stats
defaults
mode tcp
retries 3
log global
option redispatch
# option abortonclose
retries 3
timeout queue 28s
timeout connect 28s
timeout client 28s
timeout server 28s
timeout check 1s
maxconn 32000
#---------------------------------------------------------------------
# main frontend which proxys to the backends
#---------------------------------------------------------------------
frontend mlp
mode tcp
option persist
# bind 10.68.97.42:9211 ssl crt /etc/ssl/server.pem
#bind 10.68.97.42:9211
bind 10.68.97.42:9210
default_backend mlp
frontend supl
mode tcp
option persist
bind 10.68.97.42:7275
default_backend supl
#-------------
# option1 http check
#------------
backend mlp
mode http
balance roundrobin
option httpchk POST / HTTP/1.1\r\nHost: 176.16.0.8:2234\r\nContent-Length: 653\r\n\r\n{<?xml version=\"1.0\" encoding=\"gb2312\"?>\r\n<svc_init ver=\"3.2.0\">\r\n<hdr ver=\"3.2.0\">\r\n<client>\r\n<id>915948</id>\r\n<pwd>915948</pwd>\r\n<serviceid></serviceid>\r\n</client>\r\n<requestor><id>13969041845</id></requestor>\r\n</hdr>\r\n<slir ver=\"3.2.0\" res_type=\"SYNC\">\r\n<msids><msid enc=\"ASC\" type=\"MSISDN\">00000000000</msid></msids>\r\n<eqop>\r\n<resp_req type=\"LOW_DELAY\"/>\r\n<hor_acc>200</hor_acc>\r\n</eqop>\r\n<geo_info>\r\n<CoordinateReferenceSystem>\r\n<Identifier>\r\n<code>4326</code>\r\n<codeSpace>EPSG</codeSpace>\r\n<edition>6.1</edition>\r\n</Identifier>\r\n</CoordinateReferenceSystem>\r\n</geo_info>\r\n<loc_type type=\"CURRENT_OR_LAST\"/>\r\n<prio type=\"HIGH\"/>\r\n</slir>\r\n</svc_init>\r\n\r\n\r\n\r\n}
http-check expect rstring <result resid=\"4\">UNKNOWN SUBSCRIBER</result>
server mlp1 192.168.12.165:9210 check
server mlp2 192.168.12.166:9210 check
#server mlp2 192.168.12.166:9210 check
backend supl
mode tcp
source 0.0.0.0 usesrc clientip
balance roundrobin
server supl1 192.168.12.165:7275 check
server supl2 192.168.12.166:7275 check
#server supl2 192.168.12.166:7275 check

Answer 1

#Mohsin,
Thanks for your answer, it gave me the critical clue to resolve this issue.
However, my message is as bellowing, right now it can work as I want(send the specified request and check the specified response). I post it, hopefully, it may help others also. One point is, the content-length is very important.
backend mlp
mode http
balance roundrobin
option httpchk POST / HTTP/1.1\r\nUser-Agent:HAProxy\r\nHost:176.16.0.8:2234\r\nContent-Type:\ text/xml\r\nContent-Length:516\r\n\r\n91594891594813969041845000000000003200
http-check expect rstring <result resid=\"4\">UNKNOWN SUBSCRIBER</result>
server mlp1 192.168.12.165:9210 check
server mlp2 192.168.12.166:9210 check

Answer 2

I was able to get this working after a bit of experimenting.
This was my setup
HAProxy -> NGINX -> Backend
I was sniffing the requests at the NGINX stage with tcpdump to see what was actually happening.
In order to change the health check request we have to follow a hack described in the documentation to change the HTTP version and send headers:
It is possible to send HTTP headers after the string by concatenating them using rn and backslashes spaces. This is useful to send Host headers when probing a virtual host
This is the raw http check I want to send:
POST ${ENDPOINT} HTTP/1.0
Content-Type: application/json
{"body": "json"}
The big issue here is that HAProxy adds a new header by itself: Connection: close, so this is what NGINX gets:
POST ${ENDPOINT} HTTP/1.0
Content-Type: application/json
{"body": "json"}
Connection: close
This leads, at least in my case to error 400s due to a malformed request.
The fix is to add a Content-Length header:
POST ${ENDPOINT} HTTP/1.0
Content-Type: application/json
Content-Length: 16
{"body": "json"}
Connection: close
Since the Content-Length should take precedence over the actual length, this forces the last header to be ignored. This is what NGINX passes to the backend:
POST ${ENDPOINT} HTTP/1.0
Host: ~^(.+)$
X-Real-IP: ${IP}
X-Forwarded-For: ${IP}
Connection: close
Content-Length: 16
Content-Type: application/json
{"body": "json"}
This is my final check:
option httpchk POST ${ENDPOINT} HTTP/1.0\r\nContent-Type:\ application/json\r\nContent-Length:\ 16\r\n\r\n{\"body\":\"json\"}
If it's just JSON you should be ok copying and pasting this and adjusting the content length.
However, I do recommend that you follow the same procedure and sniff the actual health checks, because, with the characters one has to escape in the config file, creating the request properly can be tricky.

Answer 3

Open haproxy/conf/haproxy.conf file. Goto end of the page, you will see that there is a line 'option httpchk GET /', change GET to POST and you are done.
Let me know if you face any problem.