debian/systemd_howto - thekelleys/dnsmasq - Gitiles

 HOWTO
 =====
 dnsmasq comes with the possibility to run multiple systemd service instances on the same machine.
 There is the main service which is enabled by default via `systemctl enable dnsmasq.service` and uses the configuration from `/etc/default/dnsmasq`.

 Additional service instances can be enabled via `systemctl enable dnsmasq@<instance name>.service` that use the configuration from `/etc/default/dnsmasq.<instance name>`.
 It is recommended to use a separate configuration file and directory for each instance.
 Additionally make sure that all instances use either different ports and/or ip addresses to avoid binding collisions.

 Example setup for an instance called "alt"
 #1 File `/etc/dnsmasq.alt.conf` copied from `/etc/dnsmasq.conf`
 #2 Directory `/etc/dnsmasq.alt.d`
 #3 File `/etc/default/dnsmasq.alt` copied from `/etc/default/dnsmasq` with following adaptions:
    * The options DNSMASQ_OPTS and CONFIG_DIR point to the correct configuration file and directory.
      DNSMASQ_OPTS="... --conf-file=/etc/dnsmasq.alt.conf ..."
      CONFIG_DIR=/etc/dnsmasq.alt.d,.dpkg-dist,.dpkg-old,.dpkg-new
    * The option DNSMASQ_EXCEPT must contain "lo" to avoid that an instance becomes the machine's DNS resolver.
      DNSMASQ_EXCEPT="lo"
   * If the additional instance should bind to all IP addresses of a specific interface, e.g. "dnsalt01", then the following addition could be used:
     DNSMASQ_OPTS="... --bind-dynamic --interface=dnsalt01 ..."
     Additionally the main instance must be stopped from binding to interfaces that are used by other instances:
     DNSMASQ_OPTS="... --bind-dynamic --except-interface=dnsalt* ..."
   * If the additional instance should not use the machine's DNS resolver, normally that's the dnsmasq main instance, as upstream server, then the following addition could be used:
     IGNORE_RESOLVCONF=yes
 #4 Enable additional instance via `systemctl enable dnsmasq@alt.service`
 #5 Start additional instance without reboot via `systemctl start dnsmasq@alt.service`


 TODO
 ====
 #1 - Found shortcoming on 2019-03-10
 Only the option DNSMASQ_EXCEPT="lo" avoids that an DNS instance will be set as the machine's DNS resolver.
 This may interfere with the wish to run an additional instance on a different port on the localhost addresses.
 My suggestion in the initial Debian report [1] was to specify an explicit variable for this.

 [1] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=914305#5


 #2 - Preferred configuration way
 Should the variables DNSMASQ_INTERFACE and DNSMASQ_EXCEPT be used instead of --interface and --except-interface?  (while "lo" still has to be in DNSMASQ_EXCEPT as of now)
	HOWTO
	=====
	dnsmasq comes with the possibility to run multiple systemd service instances on the same machine.
	There is the main service which is enabled by default via `systemctl enable dnsmasq.service` and uses the configuration from `/etc/default/dnsmasq`.

	Additional service instances can be enabled via `systemctl enable dnsmasq@<instance name>.service` that use the configuration from `/etc/default/dnsmasq.<instance name>`.
	It is recommended to use a separate configuration file and directory for each instance.
	Additionally make sure that all instances use either different ports and/or ip addresses to avoid binding collisions.

	Example setup for an instance called "alt"
	#1 File `/etc/dnsmasq.alt.conf` copied from `/etc/dnsmasq.conf`
	#2 Directory `/etc/dnsmasq.alt.d`
	#3 File `/etc/default/dnsmasq.alt` copied from `/etc/default/dnsmasq` with following adaptions:
	* The options DNSMASQ_OPTS and CONFIG_DIR point to the correct configuration file and directory.
	DNSMASQ_OPTS="... --conf-file=/etc/dnsmasq.alt.conf ..."
	CONFIG_DIR=/etc/dnsmasq.alt.d,.dpkg-dist,.dpkg-old,.dpkg-new
	* The option DNSMASQ_EXCEPT must contain "lo" to avoid that an instance becomes the machine's DNS resolver.
	DNSMASQ_EXCEPT="lo"
	* If the additional instance should bind to all IP addresses of a specific interface, e.g. "dnsalt01", then the following addition could be used:
	DNSMASQ_OPTS="... --bind-dynamic --interface=dnsalt01 ..."
	Additionally the main instance must be stopped from binding to interfaces that are used by other instances:
	DNSMASQ_OPTS="... --bind-dynamic --except-interface=dnsalt* ..."
	* If the additional instance should not use the machine's DNS resolver, normally that's the dnsmasq main instance, as upstream server, then the following addition could be used:
	IGNORE_RESOLVCONF=yes
	#4 Enable additional instance via `systemctl enable dnsmasq@alt.service`
	#5 Start additional instance without reboot via `systemctl start dnsmasq@alt.service`



	TODO
	====
	#1 - Found shortcoming on 2019-03-10
	Only the option DNSMASQ_EXCEPT="lo" avoids that an DNS instance will be set as the machine's DNS resolver.
	This may interfere with the wish to run an additional instance on a different port on the localhost addresses.
	My suggestion in the initial Debian report [1] was to specify an explicit variable for this.

	[1] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=914305#5


	#2 - Preferred configuration way
	Should the variables DNSMASQ_INTERFACE and DNSMASQ_EXCEPT be used instead of --interface and --except-interface? (while "lo" still has to be in DNSMASQ_EXCEPT as of now)