How to customise machines

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MAAS allows you to customize machines before you provision them, using curtin or cloud-init.

Pre-seed curtin

You can customise the Curtin installation by either editing the existing curtin_userdata template or by adding a custom file as described above. For a flowchart, showing where Curtin and pre-seeding fits into the deployment picture, see About deploying machines.

Curtin provides hooks to execute custom code before and after installation takes place. These hooks are named early and late respectively, and they can both be overridden to execute the Curtin configuration in the ephemeral environment. Additionally, the late hook can be used to execute a configuration for a machine being installed, a state known as in-target.

Curtin commands look like this:

    foo: ["command", "--command-arg", "command-arg-value"]

Each component of the given command makes up an item in an array. Note, however, that the following won’t work:

    foo: ["sh", "-c", "/bin/echo", "foobar"]

This syntax won’t work because the value of sh’s -c argument is itself an entire command. The correct way to express this is:

    foo: ["sh", "-c", "/bin/echo foobar"]

The following is an example of an early command that will run before the installation takes place in the ephemeral environment. The command pings an external machine to signal that the installation is about to start:

early_commands:
  signal: ["wget", "--no-proxy", "http://example.com/", "--post-data", "system_id=&signal=starting_install", "-O", "/dev/null"]

The following is an example of two late commands that run after installation is complete. Both run in-target, on the machine being installed.

The first command adds a PPA to the machine. The second command creates a file containing the machine’s system ID:

late_commands:
  add_repo: ["curtin", "in-target", "--", "add-apt-repository", "-y", "ppa:my/ppa"]
  custom: ["curtin", "in-target", "--", "sh", "-c", "/bin/echo -en 'Installed ' > /tmp/maas_system_id"]

Pre-seed cloud-init

For a flowchart, showing where cloud-init fits into the deployment picture, see About deploying machines.

To customise cloud-init:

  • In the MAAS 3.4 UI, select Machines > machine > Actions > Deploy > Cloud-init user-data… > enter cloud-init customisations > Start deployment for machine.

  • With the UI for all other MAAS versions, select a machine > Take action > Deploy > > *Cloud-init user-data…" > enter desired cloud-init script > Start deployment for machine.

  • Via the CLI, use the following command:

	maas $PROFILE machine deploy $SYSTEM_ID user_data=<base-64-encoded-script>
The three replaceable parameters shown above decode to:

1.  `$PROFILE`: Your MAAS login. E.g. `admin`
2.  `$SYSTEM_ID`: The machine's system ID (see example below)
3.  `<base-64-encoded-script>`: A base-64 encoded copy of your cloud-init script. See below for an example.

Set the default minimum kernel

To set the default minimum enlistment and commissioning kernel for all machines:

  • In the MAAS 3.4 UI, select Settings > Configuration > Commissioning > Default minimum kernel version (dropdown) > Save.

  • With the UI for all other MAAS versions, select Settings > General > Default minimum kernel version (dropdown) > Save.

  • Via the MAAS CLI, use the following command:

    maas $PROFILE maas set-config name=default_min_hwe_kernel value=$KERNEL
For example, to set it to the 16.04 GA kernel:
    maas $PROFILE maas set-config name=default_min_hwe_kernel value=ga-16.04

Note that the command option default_min_hwe_kernel appears to apply to only HWE kernels but this is not the case.

Set minimum deployment kernel for one machine

To set the minimum deployment kernel on a machine basis:

  • In the MAAS UI, set Machines > machine > Configuration > Edit > Minimum kernel.

  • Via the MAAS CLI, use the following command:

    maas $PROFILE machine update $SYSTEM_ID min_hwe_kernel=$HWE_KERNEL
For example, to set it to the HWE 16.04 kernel:
    maas $PROFILE machine update $SYSTEM_ID min_hwe_kernel=hwe-16.04

Set a specific kernel during machine deployment

To set a specific kernel during deployment:

  • In the MAAS UI, select Machines > machine > Take action > Deploy > choose a kernel > Deploy machine.
    MAAS verifies that the specified kernel is available for the given Ubuntu release (series) before deploying the machine.

  • Via the MAAS CLI, use the following command:

    maas $PROFILE machine deploy $SYSTEM_ID distro_series=$SERIES hwe_kernel=$KERNEL

The operation will fail if the kernel specified by hwe_kernel is older than the kernel (possibly) given by default_min_hwe_kernel. Similarly, it will not work if the kernel is not available for the given distro series (such as ‘hwe-16.10’ for ‘xenial’).

Set global kernel boot options

To set global kernel boot options:

  • In the MAAS 3.4 UI, select Settings > Kernel parameters > enter the Global boot parameters always passed to the kernel > Save.

  • With the UI for all other versions of MAAS, select Settings > General > Global Kernel Parameters section > enter options > Save.

  • Via the MAAS CLI, you can set kernel boot options and apply them to all machines with the following command:

    maas $PROFILE maas set-config name=kernel_opts value='$KERNEL_OPTIONS'

Kernel option tags (CLI)

You can create tags with embedded kernel boot options. When you apply such tags to a machine, those kernel boot options will be applied to that machine on the next deployment.

To create a tag with embedded kernel boot options, use the following command:

maas $PROFILE tags create name='$TAG_NAME' \
    comment='$TAG_COMMENT' kernel_opts='$KERNEL_OPTIONS'

For example:

maas admin tags create name='nomodeset_tag' \
    comment='nomodeset_kernel_option' kernel_opts='nomodeset vga'

This command yields the following results:

Success.
Machine-readable output follows:
{
    "name": "nomodeset_tag",
    "definition": ",
    "comment": "nomodeset_kernel_option",
    "kernel_opts": "nomodeset vga",
    "resource_uri": "/MAAS/api/2.0/tags/nomodeset_tag/"
}

You can check your work with a modified form of the listing command:

maas admin tags read | jq -r \
'(["tag_name","tag_comment","kernel_options"]
|(.,map(length*"-"))),(.[]|[.name,.comment,.kernel_opts]) 
| @tsv' | column -t

This should give you results something like this:

tag_name             tag_comment                  kernel_options                     
--------             -----------                  --------------                     
virtual                                                                              
new_tag              a-new-tag-for-test-purposes                                     
pod-console-logging  console=tty1                 console=ttyS0                      
nomodeset_tag        nomodeset_kernel_option      nomodeset       vga

Enable hardware sync (MAAS 3.2 and higher)

MAAS hardware sync may leak the MAAS admin API token. You may need to rotate all admin tokens and re-deploy all machines that have hardware sync enabled. To find out whether this is an issue, and how to fix it, see the troubleshooting instructions for this problem.

To enable Hardware sync on a machine:

  • In the MAAS 3.4 UI, select Machines > machine > Actions > Deploy > check Periodically synch hardware > Start deployment.

  • With the UI on all other versions of MAAS, select Machines > machine > Take action > Deploy > check Periodically synch hardware > Start deployment.

  • Via the MAAS CLI, deploy the machine from the command line, adding enable_hw_sync=true:

    maas $PROFILE machine deploy $SYSTEM_ID osystem=$OSYSTEM distro_series=$VERSION enable_hw_sync=true

Once you’ve enabled hardware sync, any changes you make to the physical device, or to the VM through the VM host, will show up in the appropriate page for the deployed machine as soon as the sync interval has passed.

View updates from hardware sync

To view updates from hardware sync:

  • In MAAS UI, select Machines > machine. Any changes to the machine’s hardware configuration will be updated on the next sync. The status bar at the bottom will show times for Last synced and Next sync. Updated BMC configuration and tags can also be viewed on the machine itself.

  • Via the MAAS CLI, hardware sync updates the machine’s blockdevice, interface and device sets on a periodic basis. These can be viewed with the CLI command:

    maas $PROFILE machine read $SYSTEM_ID
The timestamps of the last time data was synced and the estimated next time the machine will be synced can be seen in the `last_sync` and `next_sync` fields respectively.

Configure hardware sync interval

The hardware sync interval is configured globally in MAAS deployment settings.


Last updated 4 days ago.