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0 pointsrwmj8y ago0 comments

(I'm not saying this is a good thing but ...) Containers are often used where you want to run several programs, but each depends on a mutually incompatible set of libraries. Two programs need python-somelib-1.0 and python-somelib-2.5, but both versions can't be installed at the same time. Or you need to upgrade the programs at different times and during the upgrade window they'd depend on different versions of python-somelib.

Now of course the correct way to solve this would be (a) to make both programs use the same version of python-somelib, (b) make upgrades happen atomically, (c) for Python modules to actually have some API backwards compatibility. But in the absence of doing the right thing you can use a container to effectively static-link everything instead. And worry about the security/bloat/management another time.

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JdeBP8y ago

You forgot possibility (d) allow multiple library versions to be present simultaneously.

btschaegg8y ago

See: Virtualenv (for Python), Snappy, Flatpack

The main advantage of docker, as far as my understanding goes, is more of a prebuilt system configuration thing. Need a database? Load the prebuilt PostgreSQL image onto the respective machine.

One thing I think should get more use in general is that Dockerfiles are essentially completely reproducible scripts[1]. Too many companies I've seen still use Word documents full of manual steps one can easily get wrong for all their machine setups (especially in the Windows world). If you want to test something quickly, you're bogged down for a day.

[1]: example: https://github.com/kstaken/dockerfile-examples/blob/master/m...

isostatic8y ago

Over the last 15 years I've built and maintained Linux distros using apt, with custom debs and pressed files which handle configuration, automatic upgrades for most systems, and a small shell script and ssh for the rest.

Now it's all docker rather than packages, ansible (which leaves no trace of what it's doing on the target machine) rather than a for I in 'cat hosts'. Fine, but where's the benefit?

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curun1r8y ago

> The main advantage of docker, as far as my understanding goes, is more of a prebuilt system configuration thing

I think the main advantage is that it standardizes the interface around the application image/container. This allows powerful abstractions to be written once rather than requiring a bespoke implementation for each way that the application is structured. Imagine writing the equivalent of Kubernetes around some hacked-together allows-multiple-versions-of-a-dependency solution. It would be a nightmare. But because the Docker image/container interfaces are codified, you can build powerful logic around those boundaries without needing to understand what's inside those images/containers. Dynamically shifting load, recovering from failures, automatic deployments and scaling are all much easier when you don't have to worry about what language the application is written in or how the application is structured.

quigonjinn8y ago

There is a way to do this without the security/bloat/management issues. Take a look at the approach of GNU Guix. Both versions of a package can coexist in the system. Libraries are dynamically-linked and security updates can be applied fast (without building the world), using the "grafting" system.

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