[Dnsmasq-discuss] Multiple instances of dnsmasq on Debian with systemd

Simon Kelley simon at thekelleys.org.uk
Sun Dec 16 22:38:52 GMT 2018


This is obviously a large amount of work, so thanks very much for that.

To make use of it, I need to be able to see as clearly as possible what
is being changed, and why. To that end, I'd much rather have diff files
ten  replacement files, but it's fairly easy to generate those for
myself. Having done that, I get vast amounts of noise where you've fixed
up indentation and end-of-line spaces, which makes seeing the actual
changes very difficult. However, reading carefully, I can see most of
what you describe, but also the reversion of all the changes that have
happened to the files since the Debian stable release.


Could I ask you to do the following?


1) Start with the latest code for the sysV init script, systemd unit and
defaults file. You can get these from the git repo at

http://thekelleys.org.uk/gitweb/?p=dnsmasq.git;a=blob_plain;f=debian/init;hb=HEAD

http://thekelleys.org.uk/gitweb/?p=dnsmasq.git;a=blob_plain;f=debian/systemd.service;hb=HEAD

http://thekelleys.org.uk/gitweb/?p=dnsmasq.git;a=blob_plain;f=debian/default;hb=HEAD


2) Make just the functional changes you've identified: no formatting or
other extraneous changes.

3) Send me context diffs (diff -u) of the changes you've made



Cheers,

Simon.


On 01/12/2018 12:20, M. Buecher wrote:
> Hello Simon,
> 
> on my first tries to start multiple dnsmasq instances on Debian 9
> "Stretch" with systemd I faced several issues and created Debian bug
> report #914305 [1].
> Yesterday I finally managed to spend several hours on the issue and
> found a clean solution for it.
> While preparing the text for the bug report I recognized that you're the
> maintainer of the Debian packages, so I decided to write to the dnsmasq
> mailing list first.
> 
> [1] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=914305
> 
> 
> 
> systemd unit files [2] allow to be used for multiple instances when the
> service unit file name ends with the at symbol (@).
> Then the service can be enabled with an instance name following the at
> symbol, e.g. `systemctl enable dnsmasq at main.service`.
> The instance name is available in an escaped format in variable %i
> (lower case) when the unit file is processed.
> The attached unit file dnsmasq at .service passes the escaped instance name
> to the init.d script (minor changes to the code plus `mv -v
> /lib/systemd/system/dnsmasq.service /lib/systemd/system/dnsmasq at .service`).
> 
> The 2nd attached file is the updated init.d script for dnsmasq.
> It now recognizes the instance name via the second script paramater and
> uses it wherever needed or possible (default file, pid file, resolvconf
> protocol, log entries).
> 
> Additionally three special cases had to be handled when running multiple
> instances of dnsmasq:
> a) The original systemd unit file wants to check the configuration
> before starting the service but does not honor the settings from the
> default file (conf file and dir).
>    Therefore the option checkconfig was added to the init.d script.
>    I don't know if there's a common SysInit V standard name for such a
> function [3].
> b) `mkdir /run/dnsmasq` in the init.d script can fail as unit files are
> run in parallel, so the directory has to be checked again if mkdir failed.
> c) Only one dnsmasq instance should be the dns resolver for the local
> system and should bind to localhost.
>    Therefore revived DNSMASQ_EXCEPT="lo" in the default file (3rd
> attached file).
> 
> Additional changes to the files are typo corrections.
> 
> [2] https://www.freedesktop.org/software/systemd/man/systemd.unit.html
> [3]
> https://www.debian.org/doc/debian-policy/ch-opersys.html#writing-the-scripts
> 
> 
> 
> 
> For testing I installed openresolv and dnsmasq on latest Debian 9
> "Stretch" and created some virtual network interfaces via systemd [4].
> The main dnsmasq instance shall run on the real NIC while special
> instances shall run on the extra virtual NICs (dnsextra*).
> 
> Stopped and disabled the original service from the Debian dnsmasq package:
> `systemctl stop dnsmasq.service`
> `systemctl disable dnsmasq.service`
> `systemctl status dnsmasq.service`
> 
> Prepared dnsmasq systemd unit file for instances by renaming and
> updating it:
> `mv -v /lib/systemd/system/dnsmasq.service
> /lib/systemd/system/dnsmasq at .service`
> 
> As instance enabled systemd unit files have to be used with an instance
> name I decided to name the default dnsmasq instance simply "main".
> Not to break SysInit V compatibility a symbol link was used for the
> "renaming" of the default file.
> `ln -s -T dnsmasq /etc/default/dnsmasq.main`
> (P.S. Other idea would be to default INSTANCE in init.d to 'main' when
> instance name not given.)
> 
> Updated also init.d script and normal default file.
> 
> Then prepared two dnsmasq instances:
> 1. Default file for main instance (/etc/default/dnsmasq.main)
> Changed to DNSMASQ_OPTS="--bind-dynamic --except-interface=dnsextra*"
> This way it will avoid binding to the extra virtual NICs while still
> recognizing new addresses and other new NICs, and it will also be the
> DNS resolver for the local system.
> 
> 2. New default file for first extra instance (/etc/default/dnsmasq.extra01)
> Copied from default file of main instance via `cp /etc/default/dnsmasq
> /etc/default/dnsmasq.extra01`
> Changed the following settings for this extra instance:
> * DNSMASQ_OPTS="--bind-dynamic --interface=dnsextra01
> --address=/heise.de/192.168.0.250"
>   Binds to one explicit interface while still recognizing new addresses.
>   One modified address resolution for testing with dig.
> * IGNORE_RESOLVCONF=yes
>   Always using /etc/resolv.conf therefore either using the dnsmasq main
> instance (if it is started) as upstream dns server or the upstream
> server from resolvconf (e.g. via DHCP).
> * DNSMASQ_EXCEPT="lo"
>   Avoid binding to localhost and also not being used as the DNS resolver
> for the local system.
> 
> With this setup I could start/stop any dnsmasq instance while keeping a
> working DNS setup.
> Additionally I could assign an explicit dnsmasq instance to any dhcp
> client.
> 
> [4] https://gist.github.com/maddes-b/e487d1f95f73f5d40805315f0232d5d9
> 
> 
> 
> I hope that I explained everything understandably, completely and in
> correct English.
> Any feedback is welcome and it would be great to see this in Debian 10 :)
> 
> Kind regards
> Maddes
> 
> 
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