Dynamic configuration is cool, but we still live in a world of static configuration. nss-etcd provides a host resolution module for GNU libc Name Service Switch (NSS). Think of it as a distributed and consistent hosts file without the complication and delay of normal DNS. nss-etcd does not require any modification to your existing DNS setup.

$ curl -L http://127.0.0.1:2379/v2/keys/database/primary -XPUT -d value="10.0.0.20"
$ ping database.primary
PING database.primary (10.0.0.20) 56(84) bytes of data.
64 bytes from 10.0.0.20: icmp_seq=1 ttl=64 time=0.320 ms

#Getting started

CMake, libyajl and a C compiler are required to build and install nss-etcd

apt-get install cmake libyajl-dev gcc

Currently etcd is also required to be running on localhost.

git clone https://github.com/ryandoyle/nss-etcd.git
cd nss-etcd
cmake -DCMAKE_INSTALL_PREFIX:PATH=/usr .
make install

nss-etcd has to be enabled in /etc/nsswitch.conf to start to be used for host resolution. Add etcd in the hosts section of this file.

hosts:          files myhostname etcd dns

Resolution is ordered left to right. For most cases, it should be before dns.

The namespace in etcd is mapped to dot-delimitered names. You have full control of the namespace you create in etcd.

$ curl -L http://127.0.0.1:2379/v2/keys/database/primary -XPUT -d value="10.0.0.20"
$ getent hosts database.primary
10.0.0.20       database.primary

• mysql/info/address -> mysql.info.address
• dns/services/db/us-east/primary -> dns.services.db.us-east.primary
• You get the idea

Bugs in nss-etcd have an impact on all processes that do name resolution. I would highly suggest that nss-etcd is not run in production environments.

nss-etcd does not cache (on purpose). It is possible that your application does cache resolution though.

Most applications will use glibc and gethostbyname but it's possible some directly query DNS by reading /etc/resolv.conf and performing their own resolution. This would bypass nss and therefore nss-etcd.

• Consul provides a DNS interface to their service discovery tool.
• SkyDNS is a DNS server built on-top of etcd