Come referenziare univocamente una entry ldap? Come legare una entry ldap con un record di un database relazionale?

Il campo entryUUID di ldap è l'esatto equivalente del campo "chiave primaria" di un db relazionale ed è un cosiddetto "attributo di sistema della entry".

Viene creato quando viene creata l'entry e non viene piu modificata. Questo è un esempio del valore che assume

entryUUID: cdc6c42e-e0c5-102c-8f62-639fb2049104

Si legge nell'RFC

A Universally Unique Identifier (UUID) is "an identifier unique
   across both space and time, with respect to the space of all UUIDs"
   [RFC 4122].  UUIDs are used in a wide range of systems.

   This document describes the 'entryUUID' operational attribute, which
   holds the UUID assigned to the object by the server.  Clients may use
   this attribute to distinguish objects identified by a particular
   distinguished name or to locate a particular object after renaming.

Ecco un esempio di entry senza attributi di sistema generata da phpldapadmin:

version: 1

# LDIF Export for: cn=Damiano Venturin,ou=contatti,dc=smoke,dc=2v,dc=ntw
# Generated by phpLDAPadmin ( http://phpldapadmin.sourceforge.net/ ) on October 10, 2008 8:46 pm
# Server: My LDAP Server (localhost)
# Search Scope: base
# Search Filter: (objectClass=*)
# Total Entries: 1

dn: cn=Damiano Venturin,ou=contatti,dc=smoke,dc=2v,dc=ntw
cn: Damiano Venturin
sn: Venturin
telephoneNumber: 031212375
mobile: 0312170xxx
otherFacsimileTelephoneNumber: 0312170xxx
objectClass: top
objectClass: person
objectClass: organizationalPerson
objectClass: inetOrgPerson
objectClass: evolutionPerson
objectClass: calEntry
homePhone: 0311234567
category: VIP
category: Business
o: 2V S.r.l.
title: Mr.
anniversary: 1005-01-04
birthDate: 1977-03-23
homePostalAddress: via San Fermo, 41$Cavallasca, Como$22020$12345$Italia
otherPostalAddress: via dei fiori, 22$Torino, Torino$22334$67890$Italy
l: Cavallasca
otherPhone: 031212375
fileAs: Venturin Damiano
note: He is really a handsome man :-D
assistantName: someone else
labeledURI: http://www.squadrainformatica.com/smak/
managerName: someone
ou: Problem solving
roomNumber:  office
spouseName: someone
businessRole: IT professionist
categories: administrator
postalAddress: via delle petunie, 666$Cavallasca, Como$22020$54321$Italy$Cav
 allasca$Cavallasca$Cavallasca
uid: dam
mail: a@squadrainformatica.com
userPassword: {md5}DIgCi/OqamoUPthG8r4epAsw==

ora la stessa entry con gli attributi di sistema:

version: 1

# LDIF Export for: cn=Damiano Venturin,ou=contatti,dc=smoke,dc=2v,dc=ntw
# Generated by phpLDAPadmin ( http://phpldapadmin.sourceforge.net/ ) on October 10, 2008 8:50 pm
# Server: My LDAP Server (localhost)
# Search Scope: base
# Search Filter: (objectClass=*)
# Total Entries: 1

dn: cn=Damiano Venturin,ou=contatti,dc=smoke,dc=2v,dc=ntw
cn: Damiano Venturin
sn: Venturin
telephoneNumber: 031212375
mobile: 0312170xxx
otherFacsimileTelephoneNumber: 0312170xxx
objectClass: top
objectClass: person
objectClass: organizationalPerson
objectClass: inetOrgPerson
objectClass: evolutionPerson
objectClass: calEntry
homePhone: 0311234567
category: VIP
category: Business
o: 2V S.r.l.
title: Mr.
anniversary: 1005-01-04
birthDate: 1977-03-23
homePostalAddress: via San Fermo, 41$Cavallasca, Como$22020$12345$Italia
otherPostalAddress: via dei fiori, 22$Torino, Torino$22334$67890$Italy
l: Cavallasca
otherPhone: 031212375
structuralObjectClass: evolutionPerson
entryUUID: cdc6c42e-e0c5-102c-8f62-639fb2049104 creatorsName: cn=admin,dc=smoke,dc=2v,dc=ntw
createTimestamp: 20080707231141Z
fileAs: Venturin Damiano
note: He is really a handsome man :-D
assistantName: someone else
labeledURI: http://www.squadrainformatica.com/smak/
managerName: someone
ou: Problem solving
roomNumber:  office
spouseName: someone
businessRole: IT professionis
categories: administrator
postalAddress: via delle petunie, 666$Cavallasca, Como$22020$54321$Italy$Cav
 allasca$Cavallasca$Cavallasca
uid: dam
mail: a@squadrainformatica.com
userPassword: {md5}DIgCi/OqamoUPthG8r4epAsw==
entryCSN: 20081005235625.520873Z#000000#000#000000
modifiersName: cn=admin,dc=smoke,dc=2v,dc=ntw
modifyTimestamp: 20081005235625Z
entryDN: cn=Damiano Venturin,ou=contatti,dc=smoke,dc=2v,dc=ntw
subschemaSubentry: cn=Subschema
hasSubordinates: FALSE

Pertanto si presta ad esser un buon hook da usare per correlare entries di ldap con record di mysql o di un qualunque altro db relazionale.

La questione poi però è: "che succede se si verifica qualche guaio e perdo i dati?" "quando ripristino il backup le UUID rimangono tali?" Ripristinando con phpldapadmin la risposta è no! Le entryUUID dei dati ripristinati differiscono dagli originali, a meno che non si utilizzino gli accorgimenti indicati nel post backup e restore di ldap