libnss-resolver

A Linux extension that adds support to the /etc/resolver/[suffix]. It supports different "nameservers" to specific suffixes. It emulates the corresponding native functionality from Mac OS X.

This is still a work in progress!

Installing

From package

Download and install the appropriate package for your Linux distribution here.

From the source (with azk)

First: install https://azk.io.

And after that:

$ git clone git@github.com:azukiapp/libnss-resolver.git
# or
$ git clone https://github.com/azukiapp-samples/libnss-resolver
$ cd libnss-resolver

# build
# [so] options: debian8-0, ubuntu12, ubuntu14, fedora20
$ azk shell [so]


# using debian8-0, ubuntu12 or ubuntu14 as [so]:

# run tests
$ azk start dns # Run a mock dns server for testing
$ azk shell [so] -t -c "scons run-test"
# or debug
$ azk shell [so] -t -c "scons run-test -Q define=DEBUG"

# install local
$ azk shell [so] -c "scons install"


# using fedora20 as [so]:

# run tests
$ azk start dns # Run a mock dns server for testing
$ azk shell [so] -t -c "scons run-test -Q prefix=/usr/lib64"
# or debug
$ azk shell [so] -t -c "scons run-test -Q define=DEBUG -Q prefix=/usr/lib64"

# install local
$ azk shell [so] -c "scons install -Q prefix=/usr/lib64"

Now you can add the resolver-nss in a resolution pipe:

$ sudo sed -i -re 's/^(hosts: .*files)(.*)$/\1 resolver\2/' /etc/nsswitch.conf

or edit /etc/nsswitch.conf:

# normally   ↓
hosts: files resolver dns
# but, if you have avahi (Zeroconf) installed
#            ↓
hosts: files resolver mdns4_minimal [NOTFOUND=return] dns mdns4 resolver

From the source (without azk)

Dependencies: scons and clang

$ git clone git@github.com:azukiapp/libnss-resolver.git
# or
$ git clone https://github.com/azukiapp/libnss-resolver.git
$ cd libnss-resolver

# build
$ scons install
# or, if you're using Fedora as SO
$ scons install -Q prefix=/usr/lib64

Now you can add the resolver-nss in a resolution pipe:

$ sudo sed -i -re 's/^(hosts: .*$)/\1 resolver/' /etc/nsswitch.conf

or edit /etc/nsswitch.conf:

# normally   ↓
hosts: files resolver dns
# but, if you have avahi (Zeroconf) installed
#            ↓
hosts: files resolver mdns4_minimal [NOTFOUND=return] dns mdns4 resolver

Configuring

After installing you can create many suffix zones in /etc/resolver/, like:

$ echo "nameserver 127.0.0.1:5353" | sudo tee -a /etc/resolver/test.resolver

Installing dnsmasq is a good way to test it:

$ sudo yum install dnsmasq
$ dnsmasq --bind-interfaces -p 5353 --no-daemon --address=/test.resolver/127.0.0.1

Now you can try this:

# ping sufix
$ ping test.resolver
# or any "subdomain"
$ ping any.test.resolver

Test and build (azk only)

This project uses clang for compiling, scons for mounting and valgrind for analyzing code runtime.

All of these tools are actually available behind the azk. So just use the commands below to get a development environment:

$ azk start dns
# [so] options: debian8-0, ubuntu12, ubuntu14, fedora20
$ azk shell [so] -t -c "scons local-install"
# or, if [so] == fedora20
$ azk shell [so] -t -c "scons local-install -Q prefix=/usr/lib64"

After that, the following scons targets are available:

# using debian8-0, ubuntu12 or ubuntu14 as so

# build and run tests
$ scons run-test -Q [define=DEBUG] [valgrind="valgrind options"]
# install in azk instance
$ scons local-install
# test:
$ ping test.resolver


# using fedora20 as so

# build and run tests
$ scons run-test -Q prefix=/usr/lib64 -Q [define=DEBUG] [valgrind="valgrind options"]
# install in azk instance
$ scons local-install -Q prefix=/usr/lib64
# test:
$ ping test.resolver

References

Inspiration code: https://github.com/danni/docker-nss
Mac OS X resolver feature: https://developer.apple.com/library/...
Simple c-ares example: https://gist.github.com/mopemope/992777
Using a dns server in c-ares: https://github.com/bagder/c-ares/blob/master/adig.c
Ip and port formats: https://sourceware.org/bugzilla/show_bug.cgi?id=14242
Using blocks in linux: http://mackyle.github.io/blocksruntime/

License

Azk source code is released under Apache 2 License.

Check LEGAL and LICENSE files for more information.

fearenales/libnss-resolver