OpenDJ: Enabling the External Change Log on a single server

Yesterday, I described how easy it is to enable Multi-Master Replication between 2 instances of OpenDJ. One of the nice thing with OpenDJ replication, is that all changes are also publicly available (subject to access control) through LDAP under the cn=changelog suffix, also nick-named the External Change Log.

But the command to enable replication and thus the External Change Log requires 2 servers. So what if you want to enable the External Change Log on a single server ?

Note that this is not a fully supported procedure, but is handy for unit testing against the External Change Log. In production environment, you will have multiple servers for high availability and thus the External Change Log will be automatically configured.

Well you cannot use the dsreplication command, but you can configure the OpenDJ instance with the dsconfig utility.

$ bin/dsconfig create-replication-server -h -p 4444 \
  -D "cn=directory manager" -w secret12 -X -n \
  --provider-name "Multimaster Synchronization" --set replication-port:8989 \
  --set replication-server-id:2 --type generic
$ bin/dsconfig create-replication-domain -h -p 4444 \
  -D "cn=directory manager" -w secret12 -X -n \
  --provider-name "Multimaster Synchronization" --set base-dn:dc=example,dc=com \
  --set --set server-id:3 \
  --type generic --domain-name example_com

If you want to be able to join this server in a replication topology, you should also create the global administrator’s entry. If you do so, then you will be able to use the dsreplication enable command as illustrated here.

$ bin/dsframework create-admin-user -X -h -p 4444 \
  -D "cn=Directory Manager" -w secret12 --userID admin --set password:password

Once enabled, you can read or search the changes with ldapsearch or other LDAP clients :

$ bin/ldapsearch -D cn=directory\ manager -w secret12 -h -p 1389 \
  -J ";" -b "cn=changelog" '(objectclass=*)'
dn: cn=changelog
cn: changelog
objectClass: top
objectClass: container

# Public changelog exchange control( dc=example,dc=com:0000012fd9bdf863000300000001;
dn: replicationCSN=0000012fd9bdf863000300000001,dc=example,dc=com,cn=changelog
targetDN: cn=a,ou=people,dc=example,dc=com
changeNumber: 0
changes:: b2JqZWN0Q2xhc3M6IHBlcnNvbgpvYmplY3RDbGFzczogdG9wCmNuOiBhCnNuOiBhCmVudH
changeType: add
changeTime: 20110510114956Z
objectClass: top
objectClass: changeLogEntry

# Public changelog exchange control( dc=example,dc=com:0000012fd9be46af000300000002;
dn: replicationCSN=0000012fd9be46af000300000002,dc=example,dc=com,cn=changelog
targetDN: cn=a,ou=people,dc=example,dc=com
changeNumber: 0
changes:: YWRkOiBkZXNjcmlwdGlvbgpkZXNjcmlwdGlvbjogTmV3IG9uZQotCnJlcGxhY2U6IG1vZG
changeType: modify
changeTime: 20110510115016Z
objectClass: top
objectClass: changeLogEntry

Note: the search above uses the “Cookie Control” which is the optimized way to search the External Change Log. The value “;” means that the “cookie” is unknown, and therefore the search starts from the first change. If you want to continue from the last change received, provide the string value that is either in the ChangeLogCookie operational attribute (returned if asked for) or the comment before the change itself.

3 thoughts on “OpenDJ: Enabling the External Change Log on a single server

  1. Mark Haine 17 November 2015 / 12:55

    Hi Ludo,

    I am working with a recent nightly build of 3.0.0 and have tried this to allow testing of change notification for an external app. Unfortunately is is not behaving as I hoped as writing changes to the directory is now rejected.

    ADD operation failed
    Result Code: 53 (Unwilling to Perform)
    Additional Information: The Replication is configured for suffix dc=external,dc=example,dc=com but was not able to connect to any Replication Server

    Can you suggest how I can fix this?


    • Ludo 17 November 2015 / 17:55

      Hi Mark,
      I’ve just tried with a very recent build of OpenDJ 3.0.0 (actually, my development environment), and the procedure still works if the Replication Domain is configured properly.

      In my first test, I used lpmac.local:8989 as the replication-server property inside my replication-domain.
      And the server was producing errors like this:

      [17/Nov/2015:17:46:21 +0100] category=org.opends.server.types.HostPort severity=ERROR msgID=org.opends.messages.replication.51 msg=The hostname lpmac.local could not be resolved as an IP address

      Trying to do an Add against the server, was resulting in the same error as you’ve described:
      Processing ADD request for uid=user.999,ou=people,dc=example,dc=com
      ADD operation failed
      Result Code: 53 (Unwilling to Perform)
      Additional Information: The Replication is configured for suffix dc=example,dc=com but was not able to connect to any Replication Server

      So I used dsconfig to modify the replication domain and set the replication-server property to localhost:8989 (which I know my server will resolve into IP

      And then things worked as expected. I could create an entry, and search the changelog:

      $ ldapsearch -D cn=directory\ manager -w secret12 -p 1389 -b cn=changelog '(&)'
      dn: cn=changelog
      objectClass: top
      objectClass: container
      cn: changelog

      dn: changeNumber=1,cn=changelog
      objectClass: top
      objectClass: changeLogEntry
      changeNumber: 1
      changeTime: 20151117164712Z
      changeType: add
      targetDN: uid=user.999,ou=people,dc=example,dc=com
      changes:: b2JqZWN0Q2xhc3M6IG9yZ2FuaXphdGlvbmFsUGVyc29uCm9iamVjdENsYXNzOiB0b3AKb2

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