High availability

Rack controller HA Region controller HA
Snap VIP

This page describes how to provide high availability (HA) for MAAS at both the rack-controller level and the region-controller level. See Concepts and terms for detailed information on what services are provided by each of those levels.

Rack controller HA

Multiple rack controllers are necessary to achieve high availability. Please see Rack controller to learn how to install rack controllers.

Multiple region endpoints

MAAS will automatically discover and track all reachable region controllers in a single cluster. It will also attempt to automatically connect to them if the one in use becomes inaccessible.

Administrators can alternatively specify multiple region-controller endpoints for a single rack controller by adding entries to /etc/maas/rackd.conf.

E.g.

.
.
.
maas_url:
  - http://<ip 1>:<port>/MAAS/
  - http://<ip 2>:<port>/MAAS/
.
.
.

BMC HA

HA for BMC control (node power cycling) is provided out of the box once a second rack controller is present. MAAS will automatically identify which rack controller is responsible for a BMC and set up communication accordingly.

DHCP HA

DHCP HA affects the way MAAS manages node, including enlistment, commissioning and deployment. It enables primary and secondary DHCP instances to serve the same VLAN. This VLAN replicates all lease information is between rack controllers. MAAS-managed DHCP is a requirement for DHCP HA.

If you are enabling DHCP for the first time after adding a second rack controller, please read Enabling DHCP.

However, if you have already enabled DHCP on your initial rack controller, you’ll need to reconfigure DHCP. Access the appropriate VLAN (via the ‘Subnets’ page) and choose action ‘Reconfigure DHCP’. There, you will see the second rack controller in the ‘Secondary controller’ field. All you should have to do is press the ‘Reconfigure DHCP’ button:

The setup of rack controller HA is now complete.

For HA purposes, DHCP provisioning will take into account multiple DNS services when there is more than one region controller on a single region.

Region controller HA

Implementing region controller HA involves setting up:

  • PostgreSQL HA
  • Secondary API server(s)

Load balancing is optional.

PostgreSQL HA

MAAS stores all state information in the PostgreSQL database. It is therefore recommended to run it in HA mode. Configuring HA for PostgreSQL is external to MAAS. You will, therefore, need to study the PostgreSQL documentation and implement the variant of HA that makes you feel most comfortable.

A quick treatment of PostgreSQL HA: hot standby is provided here for convenience only. This summary will give you an idea of the command line implementation of HA with PostgreSQL.

Each region controller uses up to 40 connections to PostgreSQL in high load situations. Running 2 region controllers requires no modifications to the max_connections in postgresql.conf. More than two region controllers require that max_connections be adjusted to add 40 more connections per extra region controller added to the HA configuration.

Secondary API server(s)

Please see Region controllers and Multiple region endpoints for more information about how to install and configure rack controllers for multiple region controllers.

Load balancing with HAProxy (optional)

You can add load balancing with HAProxy load-balancing software to support multiple API servers. In this setup, HAProxy provides access to the MAAS web UI and API.

If you happen to have Apache running on the same server where you intend to install HAProxy, you will need to stop and disable apache2, because HAProxy binds to port 80.

Install

sudo apt install haproxy

Configure

Configure each API server’s load balancer by copying the following into /etc/haproxy/haproxy.cfg (see the upstream configuration manual as a reference). Replace $PRIMARY_API_SERVER_IP and $SECONDARY_API_SERVER_IP with their respective IP addresses:

frontend maas
    bind    *:80
    retries 3
    option  redispatch
    option  http-server-close
    default_backend maas

backend maas
    timeout server 90s
    balance source
    hash-type consistent
    server localhost localhost:5240 check
    server maas-api-1 $PRIMARY_API_SERVER_IP:5240 check
    server maas-api-2 $SECONDARY_API_SERVER_IP:5240 check

where maas-api-1 and maas-api-2 are arbitrary server labels.

Now restart the load balancer to have these changes take effect:

sudo systemctl restart haproxy

The configuration of region controller HA is now complete.

The API server(s) must be now be referenced (e.g. web UI, MAAS CLI) using port 80 (as opposed to port 5240).

Snap

Setting up high-availability using snaps is relatively easy. To use snaps instead of a package distribution of MAAS:

  1. Set up PostgreSQL for high-availability as explained above. PostgreSQL should run outside of the snap.
  2. Install the MAAS snap on each machine you intend to use as a rack or region controller. You’ll need the MAAS shared secret, located here, /var/lib/maas/secret, on the first region controller you set up.
  3. Initialise the snap as a rack or region controller. Note that if you intend to use a machine as a region controller, you’ll need to tell MAAS how to access your PostgreSQL database host with the following arguments:
    • --database-host DATABASE_HOST
    • --database-name DATABASE_NAME
    • --database-user DATABASE_USER
    • --database-pass DATABASE_PASS

VIP

Note versions of MAAS below 2.5 required a virtual IP to serve as the effective IP address of all region API servers in high-availability environments. This virtual IP is not necessary for MAAS versions 2.5 and above.

On the referenced document, on adding a secondary API server, it specifies:

sudo maas-region local_config_set --database-host $PRIMARY_PG_SERVER

The question is what happens in the event of failure of the primary MAAS region controller? should it point to the hot_standby database? a.k.a localhost ?

Thanks