sdss-clu 2.2.6

A new protocol for SDSS actors.

CLU implements a new protocol for SDSS actor while providing support for legacy-style actor.

Features

• Asynchronous API based on asyncio.

• New-style actor with message passing based on AMQP and RabbitMQ.

• Legacy-style actor for TCP socket communication via tron.

• Tools for device handling.

• Messages are validated JSON strings.

• click-enabled command parser.

Installation

CLU can be installed using pip as

pip install sdss-clu

or from source

git clone https://github.com/sdss/clu
cd clu
pip install .

Development

clu uses poetry for dependency management and packaging. To work with an editable install it’s recommended that you setup poetry and install clu in a virtual environment by doing

poetry install

Pip does not support editable installs with PEP-517 yet. That means that running pip install -e . will fail because poetry doesn’t use a setup.py file. As a workaround, you can use the create_setup.py file to generate a temporary setup.py file. To install clu in editable mode without poetry, do

pip install --pre poetry
pip install -U setuptools
python create_setup.py
pip install -e .

Quick start

Creating a new actor with CLU is easy. To instantiate and run an actor you can simply do

import asyncio
from clu import AMQPActor

async def main(loop):
    actor = await Actor('my_actor').start()
    await actor.run_forever()

asyncio.run(main(loop))

Next, head to the Getting started section for more information about using actors. More examples are available here.

Why a new messaging protocol for SDSS?

Say whatever you want about it, the current SDSS message passing protocol based on Tron, opscore, and actorcore is stable and robust. So, why should we replace it? Here is a list of reasons:

• It reinvents the wheel. Ok, in all honesty Tron and opscore were written when wheel were still not completely circular, but the truth is that nowadays there are more robust, standard, and better documented technologies out there for message passing.

• We can remove the need for a central hub product by relying in open-source message brokers such as RabbitMQ.

• Tron and opscore are Python 2 and it’s unclear the amount of effort that would be needed to convert them to Python 3.

• While there is some documentation for Tron and opscore, and the code is well written, it’s also cumbersome and difficult to modify by people that didn’t write it. It’s ultimately non-maintainable.

• The opsctore/actorkeys datamodel is custom-built and extremely difficult to maintain. Standard solutions such as JSON with a JSON schema validator should be preferred.

• asyncio provides an asynchronous API that is cleaner and easier to code than using threads. It is also more readable and less convoluted than twisted and it’s a Python core library with very active development.

• CLU uses click for parsing commands, providing a well-defined, easy to use parser.