Idea for storing LTSP configuration in LDAP

[Petter Reinholdtsen <pere@hungry.com>]

Vagrant mentioned on IRC that ltsp_config now support sourcing files
from /usr/share/ltsp/ltsp_config.d/ on the thin clients, and that this
can be used to fetch configuration from LDAP if we choose to store
configuration there.

Armed with this information, I got inspired and wrote a test module to
get configuration from LDAP.  The idea is to look up the MAC address
of the client in LDAP, and look for attributes on the form
ltspconfigsetting=value, and use this to export SETTING=value to the
LTSP clients.

The goal is to be able to store the LTSP configuration attributes in a
"computer" LDAP object used by both DNS and DHCP, and thus allowing us
to store all information about a computer in one place.

This is a untested draft implementation, and I welcome feedback on
this approach.  A real LDAP schema for the ltspClientAux objectclass
need to be written.  Comments, suggestions, etc?

# Store in /opt/ltsp/$arch/usr/share/ltsp/ltsp_config.d/ldap-config
#
# Fetch LTSP client settings from LDAP based on MAC address
#
# Uses ethernet address as stored in the dhcpHost objectclass using
# the dhcpHWAddress attribute or ethernet address stored in the
# ieee802Device objectclass with the macAddress attribute.
#
# This module is written to be schema agnostic, and only depend on the
# existence of attribute names.
#
# The LTSP configuration variables are saved directly using a
# ltspConfig prefix and uppercasing the rest of the attribute name.
# To set the SERVER variable, set the ltspConfigServer attribute.
#
# Some LDAP schema should be created with all the relevant
# configuration settings.  Something like this should work:
# 
# objectclass ( 1.1.2.2 NAME 'ltspClientAux'
#     SUP top
#     AUXILIARY
#     MAY ( ltspConfigServer $ ltsConfigSound $ ... )

LDAPSERVER=$(debian-edu-ldapserver)
if [ "$LDAPSERVER" ] ; then
    LDAPBASE=$(debian-edu-ldapserver -b)
    for MAC in $(LANG=C ifconfig |grep -i hwaddr| awk '{print $5}'|sort -u) ; do
    filter="(|(dhcpHWAddress=ethernet $MAC)(macAddress=$MAC))"
    ldapsearch -h "$LDAPSERVER" -b "$LDAPBASE" -v -x "$filter" | \
        grep '^ltspConfig' | while read attr value ; do
            # Remove prefix and convert to upper case
                attr=$(echo $attr | sed 's/^ltspConfig//i' | tr a-z A-Z)
                    # bass value on to clients
                        eval "$attr=$value; export $attr"
                        done
    done
fi

I'm not sure this shell construction will work, because I suspect the
while block might end up in a subshell causing the variables set there
to not show up in ltsp-config, but if that is the case I am sure the
code can be restructured to make sure the variables are passed on.  I
expect that can be solved with some testing. :)

Happy hacking,
-- 
Petter Reinholdtsen