# 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: 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