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Lua Director ​

WARNING

This is an unsupported method of running Dovecot. Caveat emptor.

It is only intended for small-scale deployments - this is NOT designed to scale for more than a few servers.

Small scale deployments using NFS or other shared storage need a way to ensure users end up in same backend. For this purpose, a simple Lua script can be used.

The example Lua scripts comes in two variants.

The script can be run on a proxy directly, or one can have one dedicated proxy node acting as a Lua director node running the script.

Prerequisites ​

This script can use any SQL driver supported by Lua DBI.

If you have multiple Dovecot proxies, they all need the same data to route users to the correct backend. Therefore, if you use a database engine that supports data replication (such as MySQL or PostgreSQL), you can run the script on each of your proxies.

For the shard version, you will also need to install CRC32 library.

Schema ​

sql
CREATE TABLE backends (
    id int not null primary key,
    hostname varchar(255) not null unique,
    hostip varchar(255),
    state smallint not null default 0
);

CREATE TABLE user_backend (
    backend_id int not null,
    user varchar(255),
    primary key(backend_id, user)
);
sql
CREATE TABLE backends (
    id INT NOT NULL PRIMARY KEY,
    hostname VARCHAR(255) NOT NULL,
    hostip VARCHAR(255)
);

CREATE TABLE user_backend (
    backend_id INT NOT NULL,
    user_hash INT NOT NULL,
    PRIMARY KEY (backend_id, user_hash)
);

The user is routed to the backend in the user_backend table. If no entry exists, the script creates one. If you used Dovecot 2.x's director_tag functionality, you can create an entry yourself with the appropriate backend.

Configuration ​

There are few ways you can use this script.

First, is drop-in replacement for director with no authentication.

passdb {
  driver = lua
  args = file=/etc/dovecot/director.lua nopassword
  # or password=masterpass
  # you can include other keys here too, they will be
  # included in the response.
}

Alternatively, if you wish to do authentication:

passdb {
  driver = pam
  result_success = continue-ok
}

passdb {
  skip = unauthenticated
  driver = lua
  args = file=/etc/dovecot/director.lua noauthenticate
}

Operations ​

There are no built-in tools in Dovecot to manage the database (such as adding backends, kicking users, monitoring backends, etc.). You need to build your own tooling.

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