Director
========

Director can be used by <Dovecot's IMAP/POP3/LMTP proxy>
[PasswordDatabase.ExtraFields.Proxy.txt] to keep a temporary user -> mail
server mapping. As long as user has simultaneous connections, the user is
always redirected to the same server. Each proxy server is running its own
director process, and the directors are communicating the state to each others.
Directors are mainly useful for setups where all of the mail storage is seen by
all servers, such as with NFS or a cluster filesystem.

First test non-director proxying
--------------------------------

The director is simply a small add-on for Dovecot proxy. Before configuring
director, you should test that a simple proxying setup with static destination
server works. See the <Proxy> [PasswordDatabase.ExtraFields.Proxy.txt] page for
more information about how to configure it. If you have a simple setup, you can
test this easily using a static passdb:

---%<-------------------------------------------------------------------------
passdb {
  driver = static
  args = proxy=y host=10.2.0.20 nopassword=y
}
---%<-------------------------------------------------------------------------

Once finished testing, remember to remove the "host" field.

Servers
-------

You need one or more servers assigned for Dovecot proxies. The same servers
could also act as backends handling the mails, but you need to run <two
separate Dovecot configurations> [RunningDovecot.txt] in different ports. This
may get a bit confusing, so it's not recommended (although v2.1 makes it easier
with 'instance_name' setting).

The directors are going to connect to each others in a ring. For example if you
have servers called A, B and C, director will create connections A->B, B->C and
C->A.

Director configuration
----------------------

In example configuration you can configure director from
'conf.d/10-director.conf'.

Listeners
---------

Configure the listeners that director requires:

---%<-------------------------------------------------------------------------
service director {
  unix_listener login/director {
    mode = 0666
  }
  fifo_listener login/proxy-notify {
    mode = 0600
    user = $default_login_user
  }
  unix_listener director-userdb {
    mode = 0600
  }
  inet_listener {
    port = 9090
  }
}
---%<-------------------------------------------------------------------------

The port 9090 will be used for listening and connecting to other directors.
You're free to use any port number you want.

Configuring list of director servers
------------------------------------

List all of your directors in 'director_servers' setting separated by spaces.
You can use:

 * IP addresses
 * hostnames
 * hostnames that expand to multiple IPs (e.g. you could have a "directors-all"
   DNS entry that expands to all directors' IPs)

You can also add :port after the IP/host. The default port is the same as what
director service's inet_listener is using (the port 9090 above).

For example if you have 3 directors, you could set:

---%<-------------------------------------------------------------------------
director_servers = 10.1.0.2 10.1.0.3 10.1.0.4
---%<-------------------------------------------------------------------------

Configuring list of mail servers
--------------------------------

List all of your backend mail servers in 'director_mail_servers' setting
separated by spaces. You can use:

 * IP addresses
 * IP ranges (e.g. 10.2.0.10-10.2.0.30)
 * hostnames
 * hostnames that expand to multiple IPs

For example if you had 20 mail servers with consecutive IPs:

---%<-------------------------------------------------------------------------
director_mail_servers = 10.2.0.11-10.2.0.30
---%<-------------------------------------------------------------------------

Enabling director
-----------------

Enable director for the wanted login services by telling them to connect to
director socket instead of the default login socket:

---%<-------------------------------------------------------------------------
service imap-login {
  executable = imap-login director
}
service pop3-login {
  executable = pop3-login director
}
---%<-------------------------------------------------------------------------

If you want to enable director for LMTP, also set:

---%<-------------------------------------------------------------------------
# LMTP first does a passdb lookup to to see if there's a proxy field returned.
# If not, it fallbacks to doing userdb lookup.
lmtp_proxy = yes

protocol lmtp {
  auth_socket_path = director-userdb
}

# If you want lmtp-proxy listening on the network, uncomment the following:
#service lmtp {
#  inet_listener lmtp {
#    port = 24
#  }
#}
---%<-------------------------------------------------------------------------

Other settings
--------------

Directors redirect a user to the same server always the user has active
connections. The redirection is also done for a while after the last connection
already disconnected. This is mainly to avoid trouble with NFS caches that
haven't yet expired. You can configure this setting from:

---%<-------------------------------------------------------------------------
director_user_expire = 15 min
---%<-------------------------------------------------------------------------

'doveadm director move' needs to be able to connect to the 'ipc' socket. Make
sure the director process can do it:

---%<-------------------------------------------------------------------------
service ipc {
  unix_listener ipc {
    user = dovecot
  }
}
---%<-------------------------------------------------------------------------

Passdb configuration
--------------------

Your passdb must return "proxy" <extra field>
[PasswordDatabase.ExtraFields.txt], otherwise director doesn't do anything.

Director works by adding a "host" extra field to the auth reply, which contains
the temporary destination mail server. This "host" field isn't added if the
passdb lookup already returns "host". This allows configuring some users to be
always proxied to a specific server.

If the backend servers verify password, you can use static passdb for director:

---%<-------------------------------------------------------------------------
passdb {
  driver = static
  args = proxy=y nopassword=y
}
---%<-------------------------------------------------------------------------

Note that while this is the simplest director configuration, users will be
assigned to a backend before they have been authenticated.  A director
configured this way can be attacked by sending it a large number of unknown
users.  To prevent this, the director should be configured to authenticate the
user and might make use of a master password to log into the backend servers.

Doveadm server
--------------

Use these settings for both director and backends:

---%<-------------------------------------------------------------------------
service doveadm {
  inet_listener {
    # any port you want to use for this:
    port = 24245
  }
}

local 10.10.10.0/24 {
  # password to use for client authentication
  doveadm_password = secret
  # allow client to only use specified list of commands (default is all):
  #doveadm_allowed_commands =
}
---%<-------------------------------------------------------------------------

The director also needs the following configuration:

---%<-------------------------------------------------------------------------
# same port as doveadm's inet_listener
doveadm_proxy_port = 24245

protocol doveadm {
  auth_socket_path = director-userdb
}
---%<-------------------------------------------------------------------------

Now you can run doveadm commands on the director, and it'll run them
automatically on the correct backend server.

Health monitoring of backend servers
------------------------------------

Brad Davidson has written a small daemon for monitoring backend servers, and
disable/enable them on demand.
Ref:http://www.dovecot.org/list/dovecot/2010-August/051946.html

Forcefully moving users to a different backend
----------------------------------------------

This is useful if you need to do maintenance on one of the backend servers and
want (active) clients to move to a different backend:

 1. Disable any system that will undo changes you make to backend server
    weights, such as poolmon.
 2. Set the weight of the backend server to be worked on to 0: 'doveadm
    director add <backend server ip> 0'
 3. Flush current assignments to disable new connections to this server:
    'doveadm director flush <backend server ip>'
 4. *From the backend server* close all open sessions: 'doveadm kick 0.0.0.0/0'

Most IMAP clients will silently just reconnect to the (new backend) server
after being kicked (at least Apple Mail 6.0 and Thunderbird 14.0).

For moving specific users to other servers (e.g. because there are too many
"heavy users" assigned to the same backend), you can use 'doveadm director
move' command in v2.0.14+. This requires the ipc permissions to be configured
correctly (see above).

(This file was created from the wiki on 2013-05-19 04:42)
