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Configure hostname and failover ip on ubuntu

If you want to configure two ubuntu nodes in such way, that the second node is a hot standby for the other one, you will need a failover ip.

First of all, set a proper hostname for your machine by editing the /etc/hostname file. Afterwards your machine needs to be rebooted or you call sudo hostname myhostname.example.org.

Since it's still necessary to have both nodes accessible, I use the following steps to make the failover ip available on both devices.

On both machines the /etc/network/interfaces file looked for example like this (working with ip 203.0.113.220):

# Loopback device:
auto lo
iface lo inet loopback

# device: eth0
auto  eth0
iface eth0 inet static
  address   203.0.113.220
  broadcast 203.0.113.255
  netmask   255.255.255.192
  gateway   203.0.113.193
  # default route to access subnet
  up route add -net 203.0.113.192 netmask 255.255.255.192 gw 203.0.113.193 eth0

at the end, I appended (for failover ip 203.0.113.209):

allow-hotplug eth0:1
iface eth0:1 inet static
  address   203.0.113.209
  broadcast 203.0.113.209
  netmask   255.255.255.255
  gateway   203.0.113.209

So far the interface should not be visible, if you query for the inet interfaces:

# ip -f inet addr show
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN
    inet 127.0.0.1/8 scope host lo
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
    inet 203.0.113.220/26 brd 203.0.113.255 scope global eth0

If you want to bring up the alias eth0:1, use:

# ifup eth0:1
RTNETLINK answers: File exists
Failed to bring up eth0:1.

The error messages are miss-leading, it worked already:

# ip -f inet addr show
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN
    inet 127.0.0.1/8 scope host lo
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
    inet 203.0.113.220/26 brd 203.0.113.255 scope global eth0
    inet 203.0.113.209/32 brd 203.0.113.209 scope global eth0:1

If you try to use ifconfig eth0:1 up to bring it up, it will fail with: SIOCSIFFLAGS: Cannot assign requested address.

If you want to shutdown the interface again, use:

# ifconfig eth0:1 down

If you try to use ifdown eth0:1 to bring it down, it will fail with: ifdown: interface eth0:1 not configured.

In open source, ubuntu by @ 22 Dec 2013

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