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Note: The following description applies both to Postgres-XC and PostgreSQL if not described explicitly. You can read PostgreSQL as Postgres-XC except for version number, which is specific to each product.
If libpq has been compiled with LDAP support (option --with-ldap for configure) it is possible to retrieve connection options like host or dbname via LDAP from a central server. The advantage is that if the connection parameters for a database change, the connection information doesn't have to be updated on all client machines.
LDAP connection parameter lookup uses the connection service file pg_service.conf (see Section 30.16). A line in a pg_service.conf stanza that starts with ldap:// will be recognized as an LDAP URL and an LDAP query will be performed. The result must be a list of keyword = value pairs which will be used to set connection options. The URL must conform to RFC 1959 and be of the form
ldap://[hostname[:port]]/search_base?attribute?search_scope?filter
where hostname defaults to localhost and port defaults to 389.
Processing of pg_service.conf is terminated after a successful LDAP lookup, but is continued if the LDAP server cannot be contacted. This is to provide a fallback with further LDAP URL lines that point to different LDAP servers, classical keyword = value pairs, or default connection options. If you would rather get an error message in this case, add a syntactically incorrect line after the LDAP URL.
A sample LDAP entry that has been created with the LDIF file
version:1 dn:cn=mydatabase,dc=mycompany,dc=com changetype:add objectclass:top objectclass:groupOfUniqueNames cn:mydatabase uniqueMember:host=dbserver.mycompany.com uniqueMember:port=5439 uniqueMember:dbname=mydb uniqueMember:user=mydb_user uniqueMember:sslmode=require
might be queried with the following LDAP URL:
ldap://ldap.mycompany.com/dc=mycompany,dc=com?uniqueMember?one?(cn=mydatabase)
You can also mix regular service file entries with LDAP lookups. A complete example for a stanza in pg_service.conf would be:
# only host and port are stored in LDAP, specify dbname and user explicitly [customerdb] dbname=customer user=appuser ldap://ldap.acme.com/cn=dbserver,cn=hosts?pgconnectinfo?base?(objectclass=*)