HAProxy allows using a host name on the server line to retrieve its IP address using name servers.
By default, HAProxy resolves the name when parsing the
configuration file, at startup and cache the result for the process' life.This is not sufficient in some cases, such as in Amazon where a server's IP can change after a reboot or an ELB Virtual IP can change based on current workload.
This article describes how to user resolvers to process server's name resolution at run time.
1. Update haproxy.cfg
global
log 127.0.0.1 local2
chroot /var/lib/haproxy
pidfile /var/run/haproxy.pid
maxconn 4096
user haproxy
group haproxy
daemon
stats socket /var/lib/haproxy/stats
stats maxconn 1
stats timeout 120s
resolvers awsvpc
nameserver vpc 169.254.169.253:53
defaults
mode tcp
log global
retries 3
timeout connect 10s
timeout client 1m
timeout server 1m
timeout check 10s
maxconn 512
backend myweb
server disabled-server 127.0.0.1:1 disabled
server mydns XXXXXXXXXXXX.ap-northeast-1.rds.amazonaws.com:80 check port 80 resolvers awsvpc inter 2000 fall 5
Note: nameserver vpc 169.254.169.253:53 is the DNS server/ resolver to be used
2. Restart haproxy service
systemctl restart haproxy
3. Check result
~:# netstat -plunt |grep 53
tcp 0 0 127.0.0.53:53 0.0.0.0:* LISTEN 10616/systemd-resol
udp 0 0 127.0.0.53:53 0.0.0.0:* 10616/systemd-resol
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