About controllers

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Understanding controllers within the MAAS ecosystem helps to metal infrastructure. You may find it useful to tweak your controller settings based on your specific network and machine count. Even consider opting for a high availability setup for robustness.

At the core of MAAS are its controllers: region controllers and rack controllers. While the region controller is the interaction hub for operators, the rack controller focuses on delivering high-bandwidth services to the machines.

Region controllers

A region controller provides several services:

  • REST API server (TCP port 5240)
  • PostgreSQL database
  • DNS
  • caching HTTP proxy
  • Web UI

It manages either an entire data centre or a specific region and orchestrates a myriad of tasks from API request routing to keeping DNS records up to date.

Rack controllers

Rack controllers manage fabrics, offering four key services:

  • DHCP
  • TFTP
  • HTTP (for images)
  • Power management

Racks caches essential resources like OS install images for better performance.


Fabrics link otherwise isolate VLANs, so they can communicate under specific conditions.

Controllers connect

The hierarchy of communication in MAAS flows from the UI/API to the region controller, then to the rack controller, and finally to the machines. High availability (HA) setups introduce redundancy but don’t alter this fundamental flow.

Racks to machines

All communications from machines route through rack controllers. This includes everything from DNS lookups to APT cache-and-forward proxies via Squid. A unique DNS resource is created for each subnet, which machines use to find an available rack controller.

Region and rack

Messaging between the region and rack controllers involves multiple steps.

Tell me about the DHCP "next-server" statement

The next-server directive specifies the host from which a machine should load its initial boot file. In the context of MAAS, the rack controller serving DHCP roles as this host, acting as a broker for boot file delivery.

Last updated 2 months ago.