
Cyrus IMAP Server: Replication Examples
***************************************


Introduction
============

The replication system creates a link between two Cyrus mailstores: a
master and a replica system. Both systems can be live mailstores with
active users: here in Cambridge we install systems in pairs.

Typically half of the users will be using each system, and each system
replicates to its partner. In the event of a failover everyone uses
the remaining system in a pair. This is typically safe as the
IMAP/POP/SMTP servers define which of the two systems is the live
server for any given account, and the replica just plays a game of
follow my leader.

Occasionally I think about introducing some form of sanity check so
that we have to explicitly issue a command to the remaining backend
system as well as the proxies in the event of a failover.


A short example of replication in action
========================================

   Index:

     #: Annotation
     C: Command issued by client
     S: Command issued by server

   # Authentication between systems is done using SSH key based authentication:

   C: $ ssh -x cyrus-2 /usr/local/cyrus/bin/sync_server
   S: * Sync Server v0.0 [EXPERIMENTAL]

   # Create new auth_state and ask for all information about given list of
   # folders (namely user.dpc22). Returns:
   #
   #   "**" unsolicited response for each mailbox. Returns:
   #      Folder UniqueID, Name, ACL, UIDlast, timestamp for last seen update.
   #
   #   "*" response for each mail message in folder:
   #      UID, GUID, flags (other than \Seen state)

   C: user_some dpc22 user.dpc22
   S: ** 6b98205c796c6c61 user.dpc22 \
   S:     "dpc22   lrswipcda       anonymous       0      " 4151 1062945305
   S: * 1 000000000000000000000000 ()
   S: * 3697 0101003f4c56b00545000000 ()
   S: * 3919 0101003f4c56b04b2900000d ()
   S: * 3937 0101003f4c56b0514900001f ()
   S: * 4066 0101003f4c56b07422000002 ()
   S: * 4089 0101003f4c56b07e56000023 (\answered)
   S: * 4118 0101003f4c56b08328000016 ()
   S: * 4131 0101003f4c56b084d7000002 ()
   S: * 4136 0101003f4c56b087f3000001 ()
   S: * 4140 0101003f4c56b08c9d000026 ()
   S: OK User_Some finished

   # Select a folder to work with

   C: select user.dpc22
   S: OK 6b98205c796c6c61 4151 1062945305

   # Remove message with UID "1" from folder list (message which has been
   # sitting in my inbox since January, has no GUID defined)

   C: expunge 1
   S: OK Expunge Complete

   # Set some user flags on message UID "4140"

   C: setflags 4140 (hello world)
   S: OK Updated flags on 1 messages okay

   # Demonstrate that something has changed:

   C: status
   S: * 3697 0101003f4c56b00545000000 ()
   S: * 3919 0101003f4c56b04b2900000d ()
   S: * 3937 0101003f4c56b0514900001f ()
   S: * 4066 0101003f4c56b07422000002 ()
   S: * 4089 0101003f4c56b07e56000023 (\answered)
   S: * 4118 0101003f4c56b08328000016 ()
   S: * 4131 0101003f4c56b084d7000002 ()
   S: * 4136 0101003f4c56b087f3000001 ()
   S: * 4140 0101003f4c56b08c9d000026 (hello world)
   S: OK 4151

   # Now lets correct the damage that we just inflicted:

   C: $ replicate -s cyrus-2 -v -v -m user.dpc22
   S: MAILBOXES user.dpc22
   S: USER_SOME dpc22 user.dpc22
   S: SELECT user.dpc22
   S: SETFLAGS [1 msgs]
   S: UPLOAD [1 msgs]
   S: SETSEEN dpc22 ...
   S: ENDUSER

   C: $ ssh -x cyrus-2 /usr/local/cyrus/bin/sync_server
   S: * Sync Server v0.0 [EXPERIMENTAL]
   S: user_some dpc22 user.dpc22
   S: ** 6b98205c796c6c61 user.dpc22 \
   S:    "dpc22   lrswipcda       anonymous       0      " 4156 1062968731
   S: * 1 000000000000000000000000 ()
   S: * 3697 0101003f4c56b00545000000 ()
   S: * 3919 0101003f4c56b04b2900000d ()
   S: * 3937 0101003f4c56b0514900001f ()
   S: * 4066 0101003f4c56b07422000002 ()
   S: * 4089 0101003f4c56b07e56000023 (\answered)
   S: * 4118 0101003f4c56b08328000016 ()
   S: * 4131 0101003f4c56b084d7000002 ()
   S: * 4136 0101003f4c56b087f3000001 ()
   S: * 4140 0101003f4c56b08c9d000026 ()
   S: OK User_Some finished

   # Back where we started: the replication engine reinserted message UID 0
   # which was missing, and removed "hello world" from message UID 4140


Tracking messages between folders
=================================

   # I've just saved a message from my inbox into a folder named "zzz",
   # creating the folder the process.

   C: $ replicate -s cyrus-2 -v -v -m user.dpc22 user.dpc22.zzz

   Replication action on two MAILBOX objects:

   S: MAILBOXES user.dpc22 user.dpc22.zzz

   Ask server for contents of the two folders:

   S:   USER_SOME dpc22 ...

   Reserve message with given GUID in user.dpc22 so that it can be moved

   S:   RESERVE user.dpc22 ...

   Remove message from source folder (reserved copy left behind)

   S:   SELECT user.dpc22
   S:   EXPUNGE [1 msgs]
   S:   SETSEEN dpc22 ...

   Create target folder and copy in message that we reserved (doesn't have to
   be uploaded again)

   S:   CREATE user.dpc22.zzz 7f6f384c3f5ba99a
   S:      "dpc22        lrswipcda       anonymous       0       " 0 1062971802
   S: SELECT user.dpc22.zzz
   S: UPLOAD [1 msgs]
   S: SETSEEN dpc22 ...
   S: ENDUSER
