Sam Stelfox

Thoughts from a software engineer, systems hacker and Linux gubernāre.

High Availability

Packages of interest:


IPVS (IP Virtual Server) is used to present a single address in a high availability scenario for one more services.

Installation / Setup

yum install ipvsadm -y

A note about LXC containers: In order to make use of ipvsadm within an LXC container, you will also need to install the ipvsadm package on the LXC host and reboot it (optionally just load the kernel module though I don't know it by name). Additionally the simplest version, VS/NAT, requires enabling IPv4 packet forwarding which requires modification of the read-only proc filesystem and thus doesn't seem to be an easy option, there may be work arounds for this, and it may effect the other forms but they haven't been tested yet.

First pass at commands:

ipvsadm -A -t -s wlc
ipvsadm -a -t -r -g -w 1
ipvsadm -a -t -r -g -w 1

That didn't work so I rebooted to clear it all out.

yum install keepalived -y

Ah ha, Eureka moment. Inside the LXC container I can unmount the /proc/sys overlay as long as I'm root...

umount /proc/sys
echo 1 > /proc/sys/net/ipv4/ip_forward

It seems that net.ipv4.ip_nonlocal_bind isn't available within an LXC container: cat /proc/sys/net/ipv4/ip_nonlocal_bind.

Valuable sites:

Interesting use for this as a firewall: