Ipswitching in an Nginx can be done by Wackamole. Wackamole is an application that helps with making a cluster highly available. It manages a bunch of virtual IPs, that should be available to the outside world at all times. Wackamole ensures that a single machine within a cluster is listening on each virtual IP address that Wackamole manages. If it discovers that particular machines within the cluster are not alive, it will almost immediately ensure that other machines acquire these public IPs. At no time will more than one machine listen on any virtual IP. Wackamole also works toward achieving a balanced distribution of number IPs on the machine within the cluster it manages.
Wackamole operates on a cluster of tightly connected machines (all on the same LAN). It works by managing a pool of IP addresses that you expect to be available at all times. These IP addresses are virtual (meaning no machine has any of those IPs as its default IP address). Wackamole will work to ensure that all of the IP addresses in the pool are assigned as virtual IPs to the machines in the cluster. No IP address is held by more than one machine and every IP address is available.
Configure Spread
Now we need to tell Spread which machines are available inside the cluster. For this example, let’s use a simple two machine cluster (www1 and www2) available under the IP addresses 192.168.1.10 and 192.168.1.11
$ sudo vi /etc/default/spread
# Change to enable spread
ENABLED=1
# Options, see spread.1 for list
OPTIONS=”-n www1″ # www1 or www2 depending on the machine
$ sudo vi /etc/spread/spread.conf
Spread_Segment 192.168.3.255:4803 {
www1 192.168.3.140
www2 192.168.3.141
}
DebugFlags = { PRINT EXIT }
EventLogFile = /var/log/spread.log
EventTimeStamp
DangerousMonitor = false
DaemonUser = spread
DaemonGroup = spread
Once we’ve changed the configuration on one machine, we need to copy it over to the other machines and restart spread:
$ sudo /etc/init.d/spread restart
Configure Wackamole
The next step is to configure Wackamole on all machines. Like we did with Spread, we start by editing /etc/default/wackamole to make sure that Wackamole is enabled and that will run when the machine starts:
$ sudo vi /etc/default/wackamole
# Change to enable wackamole
ENABLED=1
# Options
OPTIONS=””
The next configuration file (/etc/wackamole.conf) is, luckily, very straight forward and a few changes to the default configurations are enough to get us on the right track.
Spread – Port where Spread is listening
SpreadRetryInterval – Amount of time between attempts to connect to Spread
Group – Spread group to join
Control – Location of Wackamole control socket
VirtualInterfaces – List of Virtual IP addresses that we want to make available
Arp-Cache – Collect and broadcast the IPs in our ARP table every N seconds
Notify – Define which machines to send ARP-spoofs when an IP is acquired
balance – Describes how to balance the IP addresses across the available machines
mature – Amount of time for an instance to join a group and be ready to assume virtual IPs
$ sudo vi /etc/wackamole.conf
Spread = 4803
SpreadRetryInterval = 5s
Group = www
Control = /var/run/wackamole/wackamole.it
VirtualInterfaces {
{ eth4:192.168.3.145/24 }
}
Arp-Cache = 90s
Notify {
eth4:192.168.1.1/32
arp-cache
}
balance {
AcquisitionsPerRound = all
interval = 4s
}
mature = 5s
