LXD — Assigning static IP to containers

You can also read this here on my personal web site:

https://yildiz.dev/2017/05/24/lxd-%E2%80%94-assigning-static-ip-to-containers/

By default, lxd containers get random ip from lxd-bridge system. If you want to assign static IPs (i.e with some logical or arithmetic order), good news: It is quite simple.

All we need to do is create a DNS configuration file and tell lxd to use it.

There is a configuration file lxd-bridge under /etc/default/ directory. It is created when you first run lxd init command. It is something like this:

# WARNING: This file is generated by a debconf template!
# It is recommended to update it by using “dpkg-reconfigure -p medium lxd”
# Whether to setup a new bridge or use an existing one
USE_LXD_BRIDGE=”false”
# Bridge name
# This is still used even if USE_LXD_BRIDGE is set to false
# set to an empty value to fully disable
LXD_BRIDGE=””
# Update the “default” LXD profile
UPDATE_PROFILE=”true”
# Path to an extra dnsmasq configuration file
LXD_CONFILE=””
# DNS domain for the bridge
LXD_DOMAIN=”lxd”
# IPv4
## IPv4 address (e.g. 10.0.8.1)
LXD_IPV4_ADDR=”10.0.8.100"
## IPv4 netmask (e.g. 255.255.255.0)
LXD_IPV4_NETMASK=”255.255.255.0"

Look that LXD_CONFILE. It is empty by default. We are going to put our configuration file’s path here. Let’s say we have 3 containers:

• web_server
• web_apps
• sip_server

Now create a file named dns.conf under /etc/default/ directory:

$ sudo nano /etc/default/dns.conf

Put these lines in it:

dhcp-host=web_server,10.0.8.99
dhcp-host=web_apps,10.0.8.100
dhcp-host=sip_server,10.0.8.101

The syntax is dhcp-host=container_name,ip_address.

Now update /etc/default/lxd-bridge file:

# Path to an extra dnsmasq configuration file
LXD_CONFILE=”/etc/default/dns.conf”

That’s it. To make our changes work, we need to restart lxd-bridge service:

$ sudo service lxd-bridge restart

We may need to reboot each container to take their new ip address:

$ lxc exec web_server /bin/bash
root@web_server:$ reboot

Now each container will have static ip based on our dns.conf file even if you reboot the system.