Hacking MAAS

Coding style

MAAS uses linters for Python, Go and Bash code.

Run make lint to check for issues/errors and make format to automatically reformat code.

Prerequisites

Dependencies

You can grab MAAS's code manually from Launchpad but Git makes it easy to fetch the last version of the code. First of all, install Git:

$ sudo apt install git

Then go into the directory where you want the code to reside and run:

$ git clone https://git.launchpad.net/maas && cd maas

MAAS depends on Postgres, isc-dhcp, bind9, and many other packages. To install everything that's needed for running and developing MAAS, run:

$ make install-dependencies

Careful: this will apt install many packages on your system, via sudo. It may prompt you for your password.

This will install bind9. As a result you will have an extra daemon running. If you are a developer and don't intend to run BIND locally, you can disable the daemon via sudo systemctl disable --now named.

Python development dependencies are pulled automatically from PyPI in a virtualenv located under .ve.

Git Workflow

You will want to adjust your git repository of lp:maas some before you start making changes to the code. This includes setting up your own copy of the repository and making your changes in branches.

First you will want to rename the origin remote to upstream and create a new origin in your namespace.

$ git remote rename origin upstream
$ git remote add origin git+ssh://{launchpad-id}@git.launchpad.net/~{launchpad-id}/maas

Now you can make a branch and start making changes.

$ git checkout -b new-branch

Once you have made the changes you want, you should commit and push the branch to your origin.

$ git commit -m "My change" -a
$ git push origin new-branch

Now you can view that branch on Launchpad and propose it to the maas repository.

Once the branch has been merged and your done with it you can update your git repository to remove the branch.

$ git fetch upstream
$ git checkout master
$ git merge upstream/master
$ git branch -d new-branch

Running tests

To run the whole suite:

$ make test

To run tests at a lower level of granularity:

$ ./bin/test.region src/maasserver/tests/test_api.py
$ ./bin/test.region src/maasserver/tests/test_api.py:AnonymousEnlistmentAPITest

Tests within provisioningserver are run with test.rack not test.region e.g.:

$ ./bin/test.rack src/provisioningserver/drivers/power/tests/test_mscm.py

The test runner is nose, so you can pass in options like --nocapture (short option: -s). This option is essential when using pdb so that stdout is not adulterated.

Emitting subunit

Pass the --with-subunit flag to any of the test runners (e.g. bin/test.rack) to produce a subunit stream of test results. This may be useful for parallelising test runs, or to allow later analysis of a test run. The optional --subunit-fd flag can be used to direct the results to a different file descriptor, to ensure a clean stream.

Production MAAS server debugging

When MAAS is installed from packaging it can help to enable debugging features to triage issues.

Log all API and UI exceptions

By default MAAS only logs HTTP 500 - INTERNAL_SERVER_ERROR into the regiond.log. To enable logging of all exceptions even exceptions where MAAS will return the correct HTTP status code.:

$ sudo sed -i 's/DEBUG = False/DEBUG = True/g' \
>   /usr/lib/python3/dist-packages/maasserver/djangosettings/settings.py
$ sudo service maas-regiond restart

Run regiond in foreground

It can help when debugging to run regiond a foreground process so you can interact with the regiond by placing a breakpoint in the code. Once you have placed a breakpoint into the code you want to inspect you can start the regiond process in the foreground.:

$ sudo service maas-regiond stop
$ sudo -u maas -H \
>   DJANGO_SETTINGS_MODULE=maasserver.djangosettings.settings \
>   twistd3 --nodaemon --pidfile= maas-regiond

Run rackd in foreground

It can help when debugging to run rackd a foreground process so you can interact with the rackd by placing a breakpoint in the code. Once you have placed a breakpoint into the code you want to inspect you can start the rackd process in the foreground.:

$ sudo service maas-rackd stop
$ sudo -u maas -H /usr/bin/authbind --deep /usr/bin/twistd3 --nodaemon --pidfile= maas-rackd

Development MAAS server setup

Access to the database is configured in src/maasserver/djangosettings/development.py.

The test suite sets up a development database cluster inside your branch. It lives in the db directory, which gets created on demand. You'll want to shut it down before deleting a branch; see below.

First, set up the project. This fetches all the required dependencies and sets up some useful commands in bin/:

$ make

Development using the snap

If you want to interact with real machines or VMs, it's better to use the snap. Instead of building a real snap, though, you can run

$ make snap-tree

to create an unpacked snap in the dev-snap/tree directory. That has all the contents of the snap, but it's in a plain directory instead of in a squashfs image. Using a directory is better for testing, since you can change the files in there and not rebuild the snap.

You can now install the snap:

$ sudo snap try dev-snap/tree
$ utilities/connect-snap-interfaces

Note that snap try is used instead of snap install. The maas snap should now be installed.

The latter command connects all the interfaces needed for the snap to work. This is performed automatically by snapd when installing the snap from the store, but is a manual step when installing via snap try.

$ snap list
Name          Version                 Rev   Tracking  Publisher   Notes
core          16-2.41                 7713  stable    canonical✓  core
core18        20191001                1192  stable    canonical✓  base
maas          2.7.0-8077-g.7e249fbe4  x1    -         -           try
maas-cli      0.6.5                   13    stable    canonical✓  -
snapd         2.41                    4605  stable    canonical✓  snapd

Next you need to initialize the snap, just like you would normally do:

$ sudo maas init

And now you're ready to make changes to the code. After you've change some source files and want to test them out, run the snap-tree-sync target again:

$ make snap-tree-sync

You should now see that you files were synced to the dev-snap/tree directory. Restart the pebble service to use the synced code:

$ sudo snap restart maas

VMs or even real machines can now PXE boot off your development snap. But of course, you need to set up the networking first. If you want to do some simple testing, the easiest is to create a networking in virt-manager that has NAT, but doesn't provide DHCP. If the name of the bridge that got created is virbr1, you can expose it to your container as eth1 using the following config:

eth1:
  name: eth1
  nictype: bridged
  parent: virbr1
  type: nic

Of course, you also need to configure that eth1 interface. Since MAAS is the one providing DHCP, you need to give it a static address on the network you created. For example:

auto eth1
iface eth1 inet static
  address 192.168.100.2
  netmask 255.255.255.0

Note that your LXD host will have the .1 address and will act as a gateway for your VMs.

Creating sample data

To create a local Postgres dabase tree (in the db/ directory), run:

$ make syncdb

In addition, it's possible to generate sample data in the database with:

$ make sampledata

with an optional (SAMPLEDATA_MACHINES=<n> parameter to specify how many machines to generate).

The created database can be dumped via:

$ make dumpdb

(optionally specifying DB_DUMP=filename.dump for the target file).

The resulting dump can then be imported into a different PostgreSQL server for MAAS to use.

With maas-test-db, this can be done with the following:

$ sudo cp maasdb.dump /var/snap/maas-test-db/common
$ sudo snap run --shell maas-test-db.psql \
  -c 'db-dump restore $SNAP_COMMON/maasdb.dump maassampledata'

and then updating the MAAS configuration to use the new db by editing /var/snap/maas/current/regiond.conf to point to the new database, and restarting the snap.

If an external postgres is used a command similar to the following one can be used to restore the database:

pg_restore \
  --clean \
  --if-exists \
  --no-owner \
  --no-privileges \
  --role maas \
  --disable-triggers \
  -d maassampledata maasdb.dump

You can review generated data:

$ sudo maas-test-db.psql

If you don't like an interactive psql prompt, you can connect via socket using other tools like pgcli:

$ sudo pgcli -h /var/snap/maas-test-db/common/postgres/sockets -U postgres

Configuring DHCP

MAAS requires a properly configured DHCP server so it can boot machines using PXE. MAAS can work with its own instance of the ISC DHCP server, if you install the maas-dhcp package:

$ sudo apt install maas-dhcp

Note that maas-dhcpd service definition referencese the maas-rackd service, which won't be present if you run a development service. To workaround edit /lib/systemd/system/maas-dhcp.service and comment out this line:

BindsTo=maas-rackd.service

Non-interactive configuration of RBAC service authentication

For development and automating testing purposes, it's possible to configure maas with the RBAC service in a non-interactive way, with the following:

$ sudo MAAS_CANDID_CREDENTIALS=user1:password1 maas configauth --rbac-url http://<url-of-rbac>:5000 --rbac-sevice-name <maas-service-name-in-RBAC>

This will automatically handle logging in with Candid, without requiring the user to fill in the authentication form via browser.

Database information

MAAS uses Django to manage changes to the database schema.

Be sure to have a look at Django's migration documentation before you make any change.

Changing the schema

Once you've made a model change (i.e. a change to a file in src/<application>/models/*.py) you have to run Django's makemigrations command to create a migration file that will be stored in src/<application>/migrations/builtin/.

Note that if you want to add a new model class you'll need to import it in src/<application>/models/__init__.py

Generate the migration script with:

$ ./bin/maas-region makemigrations --name description_of_the_change maasserver

This will generate a migration module named src/maasserver/migrations/builtin/<auto_number>_description_of_the_change.py. Don't forget to add that file to the project with:

$ git add src/maasserver/migrations/builtin/<auto_number>_description_of_the_change.py

To apply that migration, run:

$ make syncdb

If you're developing using the snap, you can run:

$ sudo snap run --shell maas.pebble -c "maas-region dbupgrade"

to run pending migrations.

Performing data migration

If you need to perform data migration, very much in the same way, you will need to run Django's makemigrations command. For instance, if you want to perform changes to the maasserver application, run:

$ ./bin/maas-region makemigrations --empty --name description_of_the_change maasserver

This will generate a migration module named src/maasserver/migrations/builtin/<auto_number>_description_of_the_change.py. You will need to edit that file and fill the operations list with the options that need to be performed. Again, don't forget to add that file to the project:

$ git add src/maasserver/migrations/builtin/<auto_number>_description_of_the_change.py

Once the operations have been added, apply that migration with:

$ make syncdb

Examining the database manually

If you need to get an interactive psql prompt, you can use dbshell:

$ bin/maas-region dbshell

You can use the \dt command to list the tables in the MAAS database. You can also execute arbitrary SQL. For example::

maasdb=# select system_id, hostname from maasserver_node;
                 system_id                 |      hostname
-------------------------------------------+--------------------
 node-709703ec-c304-11e4-804c-00163e32e5b5 | gross-debt.local
 node-7069401a-c304-11e4-a64e-00163e32e5b5 | round-attack.local
(2 rows)

Viewing SQL queries during tests

If you need to view the SQL queries that are performed during a test, the LogSQL fixture can be used to output all the queries during the test.:

from maasserver.testing.fixtures import LogSQL
self.useFixture(LogSQL())

Sometimes you need to see where in the code that query was performed.:

from maasserver.testing.fixtures import LogSQL
self.useFixture(LogSQL(include_stacktrace=True))