Dovecot Pro Palomar Architecture

⚠️ TODO

Right now, this intro describes the cluster service, but not Palomar in general.

We should add documentation to this page that describes:

• sites
• users
• groups
• failover groups
• routing
• health checking
• administration
• statistics
• balancing
• ???

The Dovecot Pro Palomar Architecture in v3.x replaces the director component in older Dovecot versions with a new cluster service.

The cluster service provides:

• Load balancer between Dovecot Proxies and Backends
• User-stickiness to backends
• High availability for backends and other sites
• Load redistribution / user moving
• Multi-site support

The architecture aims to serve each user via a single backend at a time. This allows caching to work efficiently. When using object storage and multiple sites, it's possible that the user is served simultaneously by multiple sites when the sites' networks don't see each other (split brain). The obox format handles this by eventually merging the changes and moving the user handling back to a single site soon after the split brain is over.

Overview

Components

• Dovecot Proxy
• Dovecot Backend
• Cluster Controller
• Palomar GeoDB
• Storage
• OX Abuse Shield

Sites

In Palomar, a site is a collection of servers intended to operate and be maintained together by a single Cluster Controller.

A single Palomar installation can contain multiple sites.

Multi-Site

⚠️ TODO

Shared Infrastructure

⚠️ TODO

Authentication

⚠️ TODO

Storage

⚠️ TODO

GeoDB?

⚠️ TODO

Other

⚠️ TODO

User Groups

Users are assigned to groups. Only groups can be moved between backends, not individual users. The number of groups should be sized approximately by the number of backends. For example counting 100 groups per backend can allow changing the backend load by 1% increments when moving groups.

Ideally all the groups have equal "load", i.e. moving any of the groups in a backend elsewhere would reduce the backend's load the same amount. A later Palomar version will support automatically moving users between groups to try to make them more balanced.

Backend Monitoring

For health-checking purposes, Palomar uses "test users" to perform a variety of actions on the Backends. These test users are using the same endpoints as users, so this more accurately measures an end user's experience rather than relying on abstract metrics and statistics.

Information on how to configure these test users can be found at Palomar Monitoring Users.

Features

Group Moving

See Palomar Group Moving.

Automatic Load Rebalancing

See Palomar Load Rebalancing.

Automatic Group Size Rebalancing

See Palomar Group Size Rebalancing.

Logging

See Palomar Logging.