Nixpanic's Blog

GlusterFS 3.5 has not been released yet, but that should happen hopefully anytime soon (currently in beta). The RPM-packaging in this version has changed a little, and now offers a glusterfs-cli package. This package mainly contains the gluster commandline interface (and pulls in any dependencies).

On of the very useful things that is now made possible, is to list the available volumes on Gluster Storge Servers. This similar functionality is used by the /etc/auto.net script to list NFS-exports that are available for mounting. The auto.net script is by default enabled after installing and starting autofs:

Automatic network configuration with DHCP is great. But if you need to use multiple separated networks at once, it gets more difficult pretty quickly. For example, my RHEL-6 laptop

1. connects through wifi to the network at home, which provides internet access
2. accesses remote systems connected via a VPN
3. and manages virtual machines that need access to any of those

Now, when NetworkManager connects to the VPN, the DNS-servers for the VPN are added to /etc/resolv.conf with a higher priority than the home network one. This is fine in a lot of circumstances, but that means all domain name
service lookups will go through the VPN first. That's not optimal, and the administrator of the VPN does not need to see all the hostname lookups my laptop is doing either. Also, any lookups for the local network will go through
the VPN, fail there and are retried with the next DNS-server, making queries for the LAN slower than all the others.

The solution sounds simple: Only use the DNS-servers on the VPN for lookups for resources that are on the VPN.

Unfortunately, the configuration is not that simple if it needs to work dynamically. The main configuration file that contains DNS-servers (/etc/resolv.conf) does not have any options to tell that some DNS-servers are to be used for certain domains only. A workaround for this limitation is to use a DNS-server that supports filtering and relaying queries, and have it listen on localhost. This DNS-server is configured in /etc/resolv.conf, and any new network configurations (or removed ones) should not change the configuration in /etc/resolv.conf, but the local DNS-server instead.

This means that my /etc/resolv.conf looks like this:
nameserver 127.0.0.1
search lan.example.net
The minimal /etc/resolv.conf file is also saved as
/etc/resolv.conf.dnsmasq, which is used as a template for restoring the configuration when a VPN service (like OpenVPN) modified it.

The DNS-server for this setup became dnsmasq. This piece of software was already installed on my laptop as a dependency of libvirt, and offers the simple configuration that this setup can benefit from. For this setup, the
libvirt configuration of dnsmasq is not touched, it works fine and with its integrated DHCP-server I am not tempted to break my virtual machines (not now, and not when I install updates).

The configuration to let dnsmasq listen on localhost, and not intervene with libvirt that listens on virbr0 is very minimal as well. My preference is to prevent big changes in packaged configuration files as these may become difficult to merge with updates, so the only change in /etc/dnsmasq.conf that is required is this (newer versions seem to have this by default):
# Include a another lot of configuration options.
#conf-file=/etc/dnsmasq.more.conf
conf-dir=/etc/dnsmasq.d
An additional file in the /etc/dnsmasq.d directory suffices,  /etc/dnsmasq.d/localhost.conf:
no-resolv
no-poll
interface=lo
no-dhcp-interface=lo
bind-interfaces
The default configuration file /etc/dnsmasq.conf contains a good description of these options. It is not needed to repeat them here.

Enabling dnsmasq to start at boot is a prerequisite, otherwise any lookup that uses DNS-servers will fail completely. On my RHEL-6 system, I needed to enable starting of dnsmasq with /sbin/chkconfig dnsmasq on, start
the service with /sbin/service dnsmasq start.

With this current configuration, only hostnames and IP-addresses that are in /etc/hosts are being resolved. Which means, it is difficult to create any network connections outside of the laptop. The next step is to integrate the available connected networks with the dnsmasq configuration.

NetworkManager is used to configure the network on my laptop. This is convenient as it supports WLAN and can connect to the VPN. In order to teach it to write a dnsmasq configuration file for each network that gets setup, I used
an event script, /etc/NetworkManager/dispatcher.d/90-update-resolv.conf:
#!/bin/sh
#
# NetworkManager dispatcher script to prevent messing with DNS servers in the
# LAN.
#
# Author: Niels de Vos
#

DNSMASQ_RESOLV=/etc/dnsmasq.d/resolv-${CONNECTION_UUID}.conf

function write_dnsmasq_header
{
if [ ! -e ${DNSMASQ_RESOLV} ]
then
echo "# ${DNSMASQ_RESOLV} generated on $(date)" > ${DNSMASQ_RESOLV}
echo "# Generator: ${0}" >> ${DNSMASQ_RESOLV}
echo "# Connection: ${CONNECTION_UUID}" >> ${DNSMASQ_RESOLV}
fi
}

function create_dnsmasq_config_env
{
local NS

write_dnsmasq_header

for NS in ${IP4_NAMESERVERS}
do
echo "server=${NS}" >> ${DNSMASQ_RESOLV}
done
}

function create_dnsmasq_config_from_resolv_conf
{
local NS
local DOMAIN=""

write_dnsmasq_header

DOMAIN=$(awk '/^domain/ {print $2}' /etc/resolv.conf)
[ -n "${DOMAIN}" ] && DOMAIN="/${DOMAIN}/"

for NS in $(awk '/^nameserver/ {print $2}' /etc/resolv.conf)
do
# make sure the NS is not from an other config
grep -q "[=/]${NS}\$" /etc/dnsmasq.d/resolv-*.conf && continue

echo "server=${DOMAIN}${NS}" >> ${DNSMASQ_RESOLV}
done
}

function remove_dnsmasq_config
{
rm -f ${DNSMASQ_RESOLV}
}

function remove_stale_configs
{
local CONF
local UUID

for CONF in /etc/dnsmasq.d/resolv-*.conf
do
# in case of a wildcard error
[ -e "${CONF}" ] || continue

UUID=$(awk '/^# Connection: / {print $3}' ${CONF})
if ! ( nmcli -t -f UUID con status | grep -q "^${UUID}\$" )
then
rm -f ${CONF}
fi
done
}

function reload_dnsmasq
{
cat /etc/resolv.conf.dnsmasq > /etc/resolv.conf
[ -n "${DHCP4_DOMAIN_SEARCH}" ] && echo "search ${DHCP4_DOMAIN_SEARCH}" >> /etc/resolv.conf
# "killall -HUP dnsmasq" is not sufficient for new files
/sbin/service dnsmasq restart 2>&1 > /dev/null
}

case "$2" in
"up")
remove_stale_configs
create_dnsmasq_config_env
reload_dnsmasq
;;
"vpn-up")
remove_stale_configs
create_dnsmasq_config_from_resolv_conf
reload_dnsmasq
;;
"down")
remove_stale_configs
remove_dnsmasq_config
reload_dnsmasq
;;
"vpn-down")
remove_stale_configs
remove_dnsmasq_config
reload_dnsmasq
;;
esac
This script will write a configuration file like /etc/dnsmasq.d/resolv-0263cda6-edbd-437e-8d36-efb86dcc9112.conf:
# /etc/dnsmasq.d/resolv-0263cda6-edbd-437e-8d36-efb86dcc9112.conf generated on Sun Mar 17 11:57:26 CET 2013
# Generator: /etc/NetworkManager/dispatcher.d/90-update-resolv.conf
# Connection: 0263cda6-edbd-437e-8d36-efb86dcc9112
server=192.168.0.1
The generated configuration file for dnsmasq simply states that there is a DNS-server on 192.168.0.1, which can be used for any query. When the configuration has been written, the dnsmasq daemon is sent a SIGHUP which causes it to reload its configuraion files.

After connecting to a VPN, an other partial configuration file is generated. In this case /etc/dnsmasq.d/resolv-ba76186a-9923-4756-aa8a-19706a4d273c.conf:
# /etc/dnsmasq.d/resolv-ba76186a-9923-4756-aa8a-19706a4d273c.conf generated on Sun Mar 17 11:57:41 CET 2013
# Generator: /etc/NetworkManager/dispatcher.d/90-update-resolv.conf
# Connection: ba76186a-9923-4756-aa8a-19706a4d273c
server=/example.com/10.0.0.1
server=/example.com/10.0.0.2
Similar to the main WLAN connection, this configuration contains two DNS-servers, but these are to be used for the example.com network only.

For me this works in the environments I visit, wifi at home, network cable connected docking station, and several other (non-)public wireless networks.

Not all projects I am regularly working on use the same CodingStyle. This is very unfortunate, and sometimes makes it time consuming to provide acceptable patches. One common example is that some project indent with a <tab>, where others expect <4-spaces>.

I could not find a vim plugin or other extension that lets me pick vim-settings per git repository. The idea that I came up with, is to set the project specific vim-settings in the git-config itself. For example:

$ git config --add vim.settings 'tabstop=4 expandtab'
Now, in my ~/.vimrc, I have the following snippet:

let git_settings = system("git config --get vim.settings")
if strlen(git_settings)
exe "set" git_settings
endif
Editing a file in the git repository that contains the above vim.settings, now replaces my <tab> by <4-spaces>. Other repositories that do not have the vim.settings will fall-back to my vim defaults. If you can think of any improvements or suggestions, please share them.