2. Development#

2.1. Overview#


ID Connector - Containers (C4 Style)#


Diagram elements#

This diagram shows - in a different style - the diagram at the top of the last chapter Administration:

  • The school management software that runs on the state level, and exports user data in a file format, e.g. CSV

  • UCS@school import which is a python script to import users into a DC Primary UCS System

  • The DC Primary UCS system passes on the user/group data to the actual ID Connector running in a docker container

  • The ID Connector finally writes user/group data to the school authorities

This, of course, is a simplification. It is on a container level (in the sense used by C4).


Arrows in these diagrams are in the direction of data flow. It should be apparent from the source and target nodes what the label on the arrow refers to.

Let’s have a look at what you need to know before we dive any deeper.

2.2. Prerequisites#

First, we assume that you are already familiar with the chapter Administration, and the prerequisites described therein.

You also need the following knowledge to follow this manual and to develop for ID Connector:


The foundation of data communication for the WWW. Our APIs use this.

You need to be able to:

  • understand HTTP messages

  • understand auth concepts

  • understand error codes


Python & pytest

The great programming language and its testing module.

You need to be able to:

  • code and debug python modules

  • test your code, ideally using pytest



The framework in which our HTTP APIs are developed.

You need to be able to:

  • understand FastAPI

  • understand dependency injection

  • understand pydantic models



Software to isolate software and run them in containers.

You need to be able to:

  • understand Dockerfile basics

  • run containers

  • understand mounts



Pluggy is the crystallized core of plugin management and hook calling (from pytest).

You need to be able to:

  • understand basic concepts of hook specs, hook implementation and hook calling


UDM REST-API (optional)

A REST API which can be used to inspect, modify, create and delete UDM objects via HTTP requests.

You will only need to know about this if you want to access extra information about objects within your (custom) plugin.

You need to be able to:

  • understand the structure of UDM objects

  • understand how to read (and maybe write) UDM objects, according to your needs


Pre-commit (optional)

A framework for managing and maintaining multi-language pre-commit hooks.

This is only needed if you need to commit to the Univention ID Connector repository.

You need to be able to:

  • install pre-commit definitions

  • run pre-commit checks

  • be aware of using different virtual environments for writing code and running pre-commits


2.3. Interactions and components#

Let’s have a closer look at what’s going on.

2.3.1. Overview, less simplified#


Diagram elements#

OK, isn’t this more or less the same as above in Overview? Yes, right, you are. The additional element is the Large in-queue. This is a folder which interacts as the interface between the DC Primary and the ID Connector. JSON files are written to the folder, and then read out.

You also may notice the get extra data arrow. This means that the ID Connector might need extra data that is not contained in the JSON files. But before we come to this, we have a closer look at the DC Primary

2.3.2. DC Primary#


Diagram elements#

  • The Univention Corporate Server import, a python script, reads in e.g. CSV data, and writes the contained user and group data to the LDAP. As mentioned in the diagram, there are other mechanisms that modify the LDAP, the UMC being one of them. The point is that user/group data “somehow” arrives.

  • The ID Connector listener python script is then called by the LDAP machinery. It handles the write events that are of interest for the ID Connector.

  • In a first step this data is written to the small in-queue. This is a folder containing minimal information (in JSON format), namely the type of change (add, update, delete) and the entryUUID of the concerned object. But why not write directly to the Converter in the next step? The reason is twofold:

    1. Speed by decoupling - the LDAP listeners should be able to do their job as fast as possible, and shouldn’t have to wait for the next processing steps. Hence the folder acting as a queue, and only writing minimal data.

    2. The folder can also act as an entry point for debugging and manual insertion of user data. E.g. you want to reschedule a user without import the user again? Use the schedule_user script, and this will write some JSON into this folder.

  • The Converter runs as a daemon script, picks up the JSON files from the small in-queue, and fetches the actual data from the LDAP using the python-ldap. It then puts a JSON representation of the UDM Object into the Large in-queue.

The Large in-queue in turn is read out by the ID Connector running in a docker container. Let’s have a closer look:

2.3.3. ID Connector#


Diagram elements#

  • We already know that the DC Primary writes data to the Large in-queue. This folder is accessible by the host UCS system as well be the ID Connector docker container (where it is mounted).

  • In Queue is a python process, that reads out the Large in-queue. It still might need extra data from the LDAP in the DC Primary, which it will do using python-ldap. For caching purposes it uses an sqlite database as a caching mechanism, the UUID record cache.

  • The In Queue decides, what user/group data to send where (using the School to authority mapping in the process). For each potential recipient there is a separate Out queue. User/group data is written in JSON format into the respective folder.

  • The JSON data is picked up the plugin processes, e.g. Out A. Usually there is only the Kelvin ID Connector plugin, which helps ID Connector to talk to Kelvin REST APIs. The Kelvin plugin process then talks to Kelvin API on the School authority A, doing the final transmission of the user/group data.

  • All this orchestrated by the Management REST API, which is mostly for managing out queues.


You have learned about Management REST API in UCS@school ID Connector HTTP API.

2.3.4. Complete picture#

The complete picture is a bit crowded. If you want see it anyway, here are your choices:

Complete overview, C4 style

Diagram elements#

Overview, manually drawn, with file locations

The ID Connector, not simplified.#

2.4. Setup#

Sadly, you can’t develop everything on your developer machine / laptop: running the ID Connector requires an LDAP, listeners etc., so you really need a full-blown UCS installation. Hence, we rather have a local checkout on the development machine, and then sync the code changes into an ID Connector container that is running on a VM.


Diagram elements#

We are going to develop with the following setup:

  • You have a git checkout of the ucsschool-id-connector on your dev machine

  • There you use the script devsync to synchronize changes,

  • which are synced to the corresponding installation folder of the ID Connector docker app.


If you don’t have devsync (from the toolshed), you might as well use scp, rsync, or any other transfer mechanism of your liking.

2.4.1. Machine#

Setup development environment:

# clone ucsschool-id-connector
$ cd ucsschool-id-connector
$ make setup_devel_env
$ . venv/bin/activate
$ make install
$ pre-commit run -a

This will create a directory venv with a Python virtual environment with the app and all its dependencies in it.

You can later on also “activate” the venv using:

$ . venv/bin/activate


All other commands in the Makefile assume that the virtualenv is activated.

Run make without argument to see more useful commands:

$ make

clean                     remove all build, test, coverage and Python artifacts
clean-build               remove build artifacts
clean-pyc                 remove Python file artifacts
clean-test                remove test and coverage artifacts
setup_devel_env           setup development environment (virtualenv)
lint                      check style (requires Python interpreter activated from venv)
format                    format source code (requires Python interpreter activated from venv)
test                      run tests with the Python interpreter from 'venv'
coverage                  check code coverage with the Python interpreter from 'venv'
coverage-html             generate HTML coverage report
install                   install the package to the active Python's site-packages
build-docker-img          build docker image locally quickly
build-docker-img-on-knut  copy source to docker.knut, build and push docker image

2.4.2. Virtual machine#

You need to install the ID Connector app through the Univention App Center on your development VM.

When started through the Univention App Center use the following to enter the container of the app:

$ univention-app shell ucsschool-id-connector

Inside the container, you can use the system Python:

# in the directory ucsschool-id-connector
$ python3
Python 3.8.2 (default, Feb 29 2020, 17:03:31)
[GCC 9.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> from ucsschool_id_connector import models
# in the directory ucsschool-id-connector
$ ipython
Python 3.8.2 (default, Feb 29 2020, 17:03:31)
Type 'copyright', 'credits' or 'license' for more information
IPython 7.13.0 -- An enhanced Interactive Python. Type '?' for help.

In [1]: from ucsschool_id_connector import models

Now, to synchronize your working copy into the running ID Connector container on the development virtual machine, we need to:

  1. Stop the ID Connector in it’s container,

  2. Find out its ID,

  3. Use this ID to sync the files into the container,

  4. Restart and prepare the container for development.

Lets do it!

# [dev VM] stop the actual ID Connector in it's docker container
$ docker exec "$(ucr get appcenter/apps/ucsschool-id-connector/container)" \
  /etc/init.d/ucsschool-id-connector stop

#[dev VM] find out the ID
$ docker inspect --format='{{.GraphDriver.Data.MergedDir}}' \
"$(ucr get appcenter/apps/ucsschool-id-connector/container)"  /var/lib/docker/overlay2/8dc...387/merged

# [developer machine] use the ID to sync our local modified files
ucsschool-id-connector$ devsync -v src/ \
<IP of dev VM>:/var/lib/docker/overlay2/8dc...387/merged/ucsschool-id-connector/

# [dev VM] enter the container
$ univention-app shell ucsschool-id-connector

# [in container] install the dev requirements
$ python3 -m pip install --no-cache-dir -r src/requirements.txt -r src/requirements-dev.txt

# [in container] install ID Connector from source in development mode
$ python3 -m pip install -e src/

# [in container] start the ID Connector
$ /etc/init.d/ucsschool-id-connector restart

# [in container] stop the Rest API
$ /etc/init.d/ucsschool-id-connector-rest-api stop

# [in container] start the REST API in auto-reloading dev mode
$ /etc/init.d/ucsschool-id-connector-rest-api-dev start

# [in container] schedule a user
$ src/schedule_user demo_teacher

# DEBUG: Searching LDAP for user with username 'demo_teacher'...
# INFO : Adding user to in-queue: 'uid=demo_teacher,cn=lehrer,cn=users,ou=DEMOSCHOOL,dc=uni,dc=dtr'.
# DEBUG: Done.

# Log is in /var/log/univention/ucsschool-id-connector/queues.log

2.4.3. Run unit tests#

Unit tests are executed as part of the build process. To start them manually in the installed apps running Docker container, run:

root@ucs-host:# univention-app shell ucsschool-id-connector
$ cd src/
$ python3 -m pytest -l -v tests/unittests
$ exit

2.5. Plugin development#

2.5.1. How does the plugin system work?#

The code of the UCS@school ID Connector app can be adapted through plugins. The pluggy plugin system is used to define, implement and call plugins.


To get a quick freshen up on Pluggy, best have a look at the toy example in the Pluggy documentation.

The basic idea:

  • specify hook specifications: callables with the signature you want to have, decorated with a hook_spec marker.

  • write actual hook implementations, a.k.a. ‘plugins’ that are later on called: callables with the same name and signature as in the specification, but this time decorated with a hook_impl marker

The hook_spec and hook_impl marker are already defined by the ID Connector system, you just need to use them. The same way, calling your custom plugin is also catered for, as well as finding your plugins.

The key file for ID Connector in this context is src/ucsschool_id_connector/plugins.py. In there you find the hook_spec and hook_impl markers.

In this file you also find the plugin specifications (function signatures) - they are decorated with @hook_spec.

The app is released with default plugins, that implement a default version for all specifications found in src/ucsschool_id_connector/plugins.py. Search for @hook_impl in src/plugins to find them.

Some of the default plugins are only used if no custom plugins are present (see usages of filter_plugins defined in src/src/ucsschool_id_connector/plugins.py):

  • create_request_keyword arguments (kwargs)

  • school_authority_ping

  • handle_listener_object

2.5.2. A simple custom plugin#

The following demonstrates a simple example of a custom plugin for ID Connector.

The directory structure for your custom plugins (and packages, see below in Advanced example) can be found in the host system in /var/lib/univention-appcenter/apps/ucsschool-id-connector/conf/:


You can put a file containing a plugin class into the plugins/plugins directory. E.g. save the following into a file called myplugin.py:

from ucsschool_id_connector.utils import ConsoleAndFileLogging
from ucsschool_id_connector.plugins import hook_impl, plugin_manager
logger = ConsoleAndFileLogging.get_logger(__name__)

class MyPlugin:

    def get_listener_object(self, obj_dict):
        logger.info("Myplugin runs get_listener_obj with %r", obj_dict)


Restart the ID Connector:

$ univention-app restart ucsschool-id-connector

Now check the queues log in /var/log/univention/ucsschool-id-connector/queues.log and find entries like this:

2021-12-13 14:32:52 INFO  [ucsschool_id_connector.plugin_loader.load_plugins:79] Loaded plugins:
2021-12-13 14:32:52 INFO  [ucsschool_id_connector.plugin_loader.load_plugins:81]     'myplugin.MyPlugin': ['get_listener_object']

This tells you that MyPlugin was found and the hook implementation for get_listener_object was found.

2.5.3. Advanced example#

In this example, you will learn how to additionally:

  • define your own hook specs

  • use an extra package for shared code across plugins.

The directory structure for a custom plugin dummy and custom package example_package below /var/lib/univention-appcenter/apps/ucsschool-id-connector/conf/ looks as follows:



Putting the example_package into the packages directory solves an import problem. As the packages directory is appended to the sys.path by the module loader in plugin_loader.py, packages herein can be imported easily without being ‘properly’ installed.

Content of plugins/packages/example_package/example_module.py:

# An example Python module that will be loadable as "example_package.example_module"
# if stored in 'plugins/packages/example_package/example_module.py'.
# Do not forget to create 'plugins/packages/example_package/__init__.py'.

from ucsschool_id_connector.utils import ConsoleAndFileLogging

logger = ConsoleAndFileLogging.get_logger(__name__)

class ExampleClass:
    def add(self, arg1, arg2):
        logger.info("Running ExampleClass.add() with arg1=%r arg2=%r.", arg1, arg2)
        return arg1 + arg2

Content of plugins/plugins/dummy.py:

# An example plugin that will be usable as "plugin_manager.hook.dummy_func()".
# It uses a class from a module in a custom package:
# plugins/packages/example_package/example_module.py

from ucsschool_id_connector.utils import ConsoleAndFileLogging
from ucsschool_id_connector.plugins import hook_impl, hook_spec, plugin_manager
from example_package.example_module import ExampleClass

logger = ConsoleAndFileLogging.get_logger(__name__)

class DummyPluginSpec:
    def dummy_func(self, arg1, arg2):
        """An example hook."""

class DummyPlugin:
    def dummy_func(self, arg1, arg2):  # <-- this must match the specification!
        Example plugin function.

        Returns the sum of its arguments.
        Uses a class from a custom package.
        logger.info("Running DummyPlugin.dummy_func() with arg1=%r arg2=%r.", arg1, arg2)
        example_obj = ExampleClass()
        res = example_obj.add(arg1, arg2)
        assert res == arg1 + arg2
        return res

# register plugins

When the app starts, all plugins will be discovered and logged:

You will then find successful messages like this in the queues log in /var/log/univention/ucsschool-id-connector/queues.log:

INFO  [ucsschool_id_connector.plugins.load_plugins:83] Loaded plugins: {.., <dummy.DummyPlugin object at 0x7fa5284a9240>}
INFO  [ucsschool_id_connector.plugins.load_plugins:84] Installed hooks: [.., 'dummy_func']

2.6. Building#

2.6.1. Build docker image#

Build the docker image:

$ make build-docker-img

The image can’t easily be used productively, so this only for testing and development purposes:

$ docker run -p --name ucsschool_id_connector \
  docker-test-upload.software-univention.de/ucsschool-id-connector:$(cat VERSION.txt)


When the container is started that way (not through the Univention App Center) it must be accessed through https://FQDN:8911/ucsschool-id-connector/api/v1/docs after stopping the firewall (service univention-firewall stop).

You can also:

# let it run in the background.
$ docker run -d ...

# see the stdout
$ docker logs ucsschool_id_connector

# stop the running container
$ docker stop ucsschool_id_connector

# remove the container
$ docker rm ucsschool_id_connector

To enter the running container run:

$ docker exec -it ucsschool_id_connector /bin/ash

2.6.2. Build release image#


You need to be an Univention developer to use this section

  • Update the apps version in VERSION.txt.

  • Add an entry to src/HISTORY.rst.

  • Build and push Docker image to Docker registry

To upload (“push”) a new Docker image to the Univention Docker registry (docker-test.software-univention.de), run:

$ cd ~/git/ucsschool-id-connector
$ make build-docker-img-on-knut

2.7. Integration tests#

Univention has automated integration tests. These are configured from this Jenkins configuration file:


If you want to manually set up integration tests, for the moment, you need to look there for hints on how to do it.