Re: Idea for storing LTSP configuration in LDAP

[Vagrant Cascadian]
> though i mentioned in our earlier chat, the LDAP schema needs to
> account for arbitrary lts.conf variables, since we're always adding
> new ones, and people should be able to easily use custom variables
> with custom hooks.

This is a good point.  One way to do this is to not use specific LDAP
attributes for each variable, but instead one generic multi-value
variable and store all settings there.  Something like this would then
be stored in LDAP:

 dn: cn=ltspConfigDefault,ou=somewhere
 objectclass: device
 objectclass: ltspClientAux
 cn=ltspConfigDefault
 ltspConfig: SERVER=ltspserver.somewhere
 ltspConfig: SOUND=N

 dn: cn=hostname,ou=somewhere
 objectclass: ieee802Device
 objectclass: domainRelatedObject
 objectclass: ltspClientAux
 cn=hostname
 macAddress: 00:01:02:03:04:05
 associatedDomain: hostname.somewhere
 ltspConfig: SOUND=N

This way, any setting can be stored in LDAP without extending the
schema.  The LDAP schema would be a lot simpler too:

attributetype ( some-OID NAME 'ltspConfig'
    DESC 'LTSP config setting'
    SYNTAX 1.3.6.1.4.1.1466.115.121.1.15 )

objectclass ( some-OID NAME 'ltspClientAux'
    DESC 'LTSP client configuration attributes'
    SUP top
    AUXILIARY
    MAY ( ltspConfig ))

> also, because we're dealing with shell variables, making sure that
> things are properly quoted and/or escaped needs to be considered
> (wheee).

I am sure this detail can be fixed.  There might also be a problem to
locate the LDAP server before resolv.conf is set up, but it would be
solvable using IP addresses instead, or making sure resolv.conf is set
up before the ltsp_config.d fragments is executed.

I rewrote my draft implementation for a ltsp_config.d script, and now
it look like this:

# 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 as 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:
#
# attributetype ( 1.1.1.1 NAME 'ltspConfig'
#    DESC 'LTSP config setting'
#    SYNTAX 1.3.6.1.4.1.1466.115.121.1.15 )
#
# objectclass ( 1.1.2.1 NAME 'ltspClientAux'
#    DESC 'LTSP client configuration attributes'
#    SUP top
#    AUXILIARY
#    MAY ( ltspConfig ))
#
# Example LDAP object:
#
# dn: cn=ltspConfigDefault,ou=somewhere
# objectclass: device
# objectclass: ltspClientAux
# cn=ltspConfigDefault
# ltspConfig: SERVER=ltspserver.somewhere
# ltspConfig: SOUND=N
#
# dn: cn=hostname,ou=somewhere
# objectclass: ieee802Device
# objectclass: domainRelatedObject
# objectclass: ltspClientAux
# cn=hostname
# macAddress: 00:01:02:03:04:05
# associatedDomain: hostname.somewhere
# ltspConfig: SOUND=N

#
# GOSA also have a LDAP approach for the tftp content (PXE arguments),
# searching for
#
# filter => "(&(macAddress=$mac)(objectClass=gotoTerminal))",
# attrs => [ 'gotoTerminalPath', 'gotoBootKernel',
#            'gotoKernelParameters', 'gotoLdapServer', 'cn' ] );
#
# See the fts-ltsp-ldap package for this.  The gotoTerminal object
# class is auxiliary, allowing it to be combined with other
# objectclasses.

setup_from_ldap() {
    filter="(&(ltspConfig=*)$1)"
    # Use temporary file to ensure the while loop is running in this
    # process, and not a subprocess.
    tempfile=$(tempfile)
    ldapsearch -h "$LDAP_HOST" -b "$BASE_DN" -v -x "$filter" ltspConfig | \
        awk '/^ltspConfig: [^=]*=[^;]*$/ { print $2}' > $tempfile
    if [ -s "$tempfile" ] ; then
    . $tempfile
        foundinldap=true
    fi
    rm $tempfile
}

lookup_mac_addrs() {
    PATH=/sbin:$PATH LANG=C ifconfig | grep -i hwaddr | awk '{print $5}' | sort -u
}

if [ -z "$LDAP_HOST" ] ; then
    LDAP_HOST=$(debian-edu-ldapserver)
fi

if [ "$LDAP_HOST" ] ; then
    if [ -z "$BASE_DN" ] ; then
    BASE_DN=$(debian-edu-ldapserver -b)
    fi

    if [ "$BASE_DN" ] ; then
        # First set default values if found
        setup_from_ldap '(cn=ltspConfigDefault)'

        # Next, look up the host MAC address(es).
        foundinldap=false
        for MAC in $(lookup_mac_addrs) ; do
            filter="(|(dhcpHWAddress=ethernet $MAC)(macAddress=$MAC))"
            setup_from_ldap "$filter"
            done

        # If the HW MAC address was not found, look for the host name
        # instead.
        if [ false = "$foundinldap" ] ; then
            hostname=$(uname -n)
            setup_from_ldap "(associatedDomain=$hostname)"
            fi
    fi
fi

Happy hacking,
-- 
Petter Reinholdtsen


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