selfhosted-apps-docker/dnsmasq

dnsmasq

guide by example

Purpose

Lightweight DHCP and DNS server.

• Official site
• Arch wik

Files and directory structure

/etc/
├── dnsmasq.conf
├── hosts
└── resolve.conf

• dnsmasq.conf - the main config file for dnsmasq where DNS and DHCP server is set
• resolve.conf - a file containing ip addresses of DNS nameservers to be used by the machine it resides on
• hosts - a file that can provide additional hostname-ip mapping

hosts and resolve.conf are just normal system files always in use on any linux system.

Installation

Install dnsmasq from your linux official repos.

Configuration

Configuration file location: /etc/dnsmasq.conf

dnsmasq.conf

# DNS --------------------------------------------------------------------------

# Never forward plain names (without a dot or domain part)
domain-needed
# Never forward addresses in the non-routed address spaces.
bogus-priv

# If you don't want dnsmasq to read /etc/resolv.conf
no-resolv
no-poll

# DHCP and DNS interface and address
interface=enp0s25
listen-address=::1,127.0.0.1

# Upstream Google and Cloudflare nameservers
server=8.8.8.8
server=1.1.1.1

# DNS wildcards ----------------------------------------------------------------

# wildcard DNS entry sending domain and all its subdomains to an ip
address=/blabla.org/192.168.1.2
# subdomain override
address=/plex.blabla.org/192.168.1.3

# DHCP -------------------------------------------------------------------------

dhcp-range=192.168.1.51,192.168.1.199,255.255.255.0,480h
# gateway
dhcp-option=3,192.168.1.1

dhcp-authoritative

#dhcp-leasefile=/var/lib/misc/dnsmasq.leases

resolv.conf

Contains DNS nameservers to be used by this linux machine.
Since dnsmasq, a DNS server, is running right on this machine, the entries should point to localhost.

Bit of an issue is that this file is often changed by various system services, like systemd or dhcpcd. To prevent this, resolv.conf will be flagged as immutable, which prevents all possible changes to it unless the attribute is removed.

Edit /etc/resolv.conf and set localhost as the DNS nameserver.

resolv.conf

nameserver ::1
nameserver 127.0.0.1

Make it immutable to prevent any changes to it.

• chattr +i /etc/resolv.conf

Check if the content is what was set.

• cat /etc/resolv.conf

If it was changed by dhcpcd before the +i flag took effect, edit /etc/dhcpcd.conf and add nohook resolv.conf at the end.
Restart the machine, disable the immutability, edit it again, add immutability, and check.

• sudo chattr -i /etc/resolv.conf
• sudo nano /etc/resolv.conf
• sudo chattr +i /etc/resolv.conf
• cat /etc/resolv.conf

/etc/hosts

dnsmasq reads /etc/hosts for IP hostname pairs entries. This is where you can add hostnames you wish to route to any ip you want.

Unfortunately no wildcard support. But as seen in the dnsmasq.conf there is a wildcard section solving this, so blabla stuff here is just for show.

hosts

127.0.0.1       docker-host
192.168.1.2     docker-host 
192.168.1.1     gateway
192.168.1.2     blabla.org
192.168.1.2     nextcloud.blabla.org
192.168.1.2     book.blabla.org
192.168.1.2     passwd.blabla.org
192.168.1.2     grafana.blabla.org

Start the service

Make sure you disable other DHCP servers on the network beforehand, usually a router is running one.

sudo systemctl enable --now dnsmasq

Test it

DHCP

Set some machine to use DHCP for its network setting.
It should just work.

You can check on the dnsmasq host, file /var/lib/misc/dnsmasq.leases for the active leases. Location of the file can vary base on your linux distro.

DNS

nslookup is utility that checks DNS mapping, part of bind-utils or bind-tools, again depending on the distro.

• nslookup google.com
• nslookup gateway
• nslookup docker-host
• nslookup blabla.org
• nslookup whateverandom.blabla.org
• nslookup plex.blabla.org

Update

During host linux packages update.

Backup and restore

Backup

Using BorgBackup setup that makes daily snapshot of the entire /etc directory which contains the config files.

restore

Replace the config files with the one from backup