selfhosted-apps-docker/dnsmasq

dnsmasq

guide by example

Purpose & Overview

Lightweight DHCP and DNS server.

• Official site
• Arch wiki

dnsmasq solves the problem of accessing self hosted stuff when you are inside your network. As asking googles DNS for blabla.org will return your very own public IP and most routers/firewalls wont allow this loopback, where your requests should go out and then right back.
Usual quick way to solve this issue is editing the hosts file on your machine, but if more devices should "just work" it is a no-go.
So the answer is running a DNS server that pairs the local machines IP with the correct hostnames, and a DHCP server that tells the devices on the network to use this DNS.

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.
dnsmasq.conf comes with the dnsmasq installation.

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-authoritative
dhcp-range=192.168.1.50,192.168.1.200,255.255.255.0,480h
# gateway
dhcp-option=option:router,192.168.1.1

# DHCP static IPs --------------------------------------------------------------
# mac address : ip address

dhcp-host=08:00:27:68:f9:bf,192.168.1.150

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

extra info

• dnsmasq --test - validates the config
• dnsmasq --help dhcp - lists all the DHCP options

resolv.conf

A file that contains DNS nameservers to be used by the linux machine, specifically its glibc resolver library.
Since dnsmasq, a DNS server, is running right on this machine, the entries should just point to localhost.

Bit of an issue is that this file is often managed by various system services, like dhcpcd, systemd, networkmanager... and they change it as they see fit.
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

This is a file present on every system, linux, windows, mac, android,... where you can assign a hostname to an IP.
dnsmasq reads /etc/hosts for IP hostname pairs and adds them to its own resolve records.

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

sudo systemctl enable --now dnsmasq

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

Test it

DHCP

Set some machine on the network 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 content of the config files with the one from the backup.