[RFR] Introduce component inheritance

[manuquentin]

applications:
    producer:
        type: python
        volumes:
            .: /app
        after_script: python /app/app.py
        custom:
            pip_modules: [pika==0.9.8]

    worker1:
        after_script: python /app/worker.py
        extends: producer

    worker2:
        after_script: python /app/worker.py
        extends: producer

• Allows component inheritance
• Add tests on component inheritance
• Add a rabbitMQ template
• Add a python/RabbitMQ example with component inheritance

[Cethy]

I would suggest to separate the "blueprints" and the actual applications ; with the example you gave, I guess producer is an application like worker1 & worker2 but it doesn't seems straightforward.

How about a "blueprints" section (like "binaries") ?

applications:
    worker1:
        extends: producer
    worker2:
        extends: producer
blueprints:
    producer:
        type: python
        ...

In the same spirit, how about a "volumes" section ? or even better, some kind of "parameter management" ?

[manuquentin]

Thanks for the suggestion.
I think adding a blueprints section will introduce complexity in the configuration file (and the builder).
The idea behind the extends param is to clone properties of an application and override some.

Same for volumes, you are free to extends an application that declare multiple volumes to avoid redeclaration of these volumes

[Cethy]

For volumes, the problem is quite different IMHO :
In a web app environment, the volumes are shared between the different apps & frontend. If I move my volume, I must edit every entries.
With the help of extends I will only write 2 "types" (app & front) of docker & extends them on other dockers. But even if it's limited to 2 entries, it is still one too many.

[manuquentin]

You're right for volumes. Containers sharing the same set of volumes aren't necessary the same type.
There is no notion of inheritance for 2 different things.

I'll think about a volumes entry and implement it in another PR.

[Cethy]

great ! 👍