The scenario: High-availability setup with 2 HAProxy/Keepalived load-balancers on a dualstack IPv4/IPv6 setup.
The problem: HAProxy won’t start (cannot bind socket) because the virtual IPv6 address is not assigned.
With IPv4, you can set the sysctl parameter: net.ipv4.ip_nonlocal_bind=1
The solution: configure the floating/virtual IPv6 address on the LOOPBACK interface
[root@kvm-lb02 haproxy]# /sbin/ip -6 addr add 2001:1af8:4500:a004:1::80/64 dev lo
