Getting Started with MAAS and Juju: MAAS Overview

For a while, I have been wanting to write about MAAS and how it can easily deploy workloads (specially OpenStack) with Juju, and the time has finally come. This will be the first of a series of posts where I’ll provide an Overview of how to quickly get started with MAAS and Juju.

What is MAAS?

I think that MAAS does not require introduction, but if people really need to know, this awesome video will provide a far better explanation than the one I can give in this blog post.


Components and Architecture

MAAS have been designed in such a way that it can be deployed in different architectures and network environments. MAAS can be deployed as both, a Single-Node or Multi-Node Architecture. This allows MAAS to be a scalable deployment system to meet your needs. It has two basic components, the MAAS Region Controller and the MAAS Cluster Controller.

MAAS Architectures

Region Controller

The MAAS Region Controller is the component the users interface with, and is the one that controls the Cluster Controllers. It is the place of the WebUI and API. The Region Controller is also the place for the MAAS meta-data server for cloud-init, as well as the place where the DNS server runs. The region controller also configures a rsyslogd server to log the installation process, as well as a proxy (squid-deb-proxy) that is used to cache the debian packages. The preseeds used for the different stages of the process are also being stored here.

Cluster Controller

The MAAS Cluster Controller only interfaces with the Region controller and is the one in charge of provisioning in general. The Cluster Controller is the place the TFTP and DHCP server(s) are located. This is the place where both the PXE files and ephemeral images are being stored. It is also the Cluster Controller’s job to power on/off the managed nodes (if configured).

The Architecture

As you can see in the image above, MAAS can be deployed in both a single node or multi-node. The way MAAS has being designed makes MAAS highly scalable allowing to add more Cluster Controllers that will manage a different pool of machines. A single-node scenario can become in a multi-node scenario by simply adding more Cluster Controllers. Each Cluster Controller has to register with the Region Controller, and each can be configured to manage a different Network. The way has this is intended to work is that each Cluster Controller will manage a different pool of machines in different networks (for provisioning), allowing MAAS to manage hundreds of machines. This is completely transparent to users because MAAS makes the machines available to them as a single pool of machines, which can all be used for deploying/orchestrating your services with juju.

How Does It Work?

MAAS has 3 basic stages. These are Enlistment, Commissioning and Deployment which are explained below:

MAAS Process


The enlistment process is the process on which a new machine is registered to MAAS. When a new machine is started, it will obtain an IP address and PXE boot from the MAAS Cluster Controller. The PXE boot process will instruct the machine to load an ephemeral image that will run and perform an initial discovery process (via a preseed fed to cloud-init). This discovery process will obtain basic information such as network interfaces, MAC addresses and the machine’s architecture. Once this information is gathered, a request to register the machine is made to the MAAS Region Controller. Once this happens, the machine will appear in MAAS with a Declared state.


The commissioning process is the process where MAAS collects hardware information, such as the number of CPU cores, RAM memory, disk size, etc, which can be later used as constraints. Once the machine has been enlisted (Declared State), the machine must be accepted into the MAAS in order for the commissioning processes to begin and for it to be ready for deployment. For example, in the WebUI, an “Accept & Commission” button will be present. Once the machine gets accepted into MAAS, the machine will PXE boot from the MAAS Cluster Controller and will be instructed to run the same ephemeral image (again). This time, however, the commissioning process will be instructed to gather more information about the machine, which will be sent back to the MAAS region controller (via cloud-init from MAAS meta-data server). Once this process has finished, the machine information will be updated it will change to Ready state. This status means that the machine is ready for deployment.


Once the machines are in Ready state, they can be used for deployment. Deployment can happen with both juju or the maas-cli (or even the WebUI). The maas-cli will only allow you to install Ubuntu on the machine, while juju will not only allow you to deploy Ubuntu on them, but will allow you to orchestrate services. When a machine has been deployed, its state will change to Allocated to <user>. This state means that the machine is in use by the user who requested its deployment.

Releasing Machines

Once a user doesn’t need the machine anymore, it can be released and its status will change from Allocated to <user> back to Ready. This means that the machine will be turned off and will be made available for later use.

But… How do Machines Turn On/Off?

Now, you might be wondering how are the machines being turned on/off or who is the one in charge of that. MAAS can manage power devices, such as IPMI/iLO, Sentry Switch CDU’s, or even virsh. By default, we expect that all the machines being controlled by MAAS have IPMI/iLO cards. So if your machines do, MAAS will attempt to auto-detect and auto-configure your IPMI/iLO cards during the Enlistment and Commissioning processes. Once the machines are Accepted into MAAS (after enlistment) they will be turned on automatically and they will be Commissioned (that is if IPMI was discovered and configured correctly).. This also means that every time a machine is being deployed, they will be turned on automatically.

Note that MAAS not only handles physical machines, it can also handle Virtual Machines, hence the virsh power management type. However, you will have to manually configure the details in order for MAAS to manage these virtual machines and turn them on/off automatically.

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