Standard project structure

[erikns]

This PR introduces a more standardized Go module structure, making it easier to build and work with. I realize it might be a bit "disruptive", but I think it's a good idea.

• The code in the app/ folder is moved out to the project root.
• The module definition file used an unrelated GitHub URL. This is changed.
• Bumped minimum Go version to 1.21 as the dependency github.com/prometheus/client_golang (at least when downloaded in the original Dockerfile seemed to require it.
• The Dockerfile is retooled to build with this new structure.

There is also a small change to the message loop in main(), I guess caused by a breaking change in the later version of govici.

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Using the new structure it is now trivial to build both "natively" or in Docker.

Natively:

• Clone
• go mod download
• go build -o ipsec-exporter .

Docker:

• docker build [...]

Cross-compilations are just as simple, should it be required.

[LarsTi]

Hey, i appreciate your work.
Temporarly i am very busy and wont get into it before eastern 2025. But i will try to check in and see at your changes.
Do you know, why the go sum file is in the commit? i was trying to keep it small and let go build the sum file in the container itself.
Thanks for your help! :)

[erikns]

I thought this project might be useful, so I figured I'd contribute back.

Do you know, why the go sum file is in the commit?

The short answer is that it enables reproducible builds, by ensuring that everyone uses the exact same versions of all dependencies. With it committed, you get the same deps (or at least you have the means to verify it) inside and outside Docker as well. Check here for some official rationale about committing the go.sum file.

[LarsTi]

I will try to merge this tommorrow when i can check this in my dev system.
Thanks for your work!

I tried to abstract the go.sum so you can just rebuild the image and all the newest components get pulled directly.
You have any ideas, how we can achieve this?

[erikns]

Do you mean the build process should get the "latest" versions automatically?

There are go mod commands to "upgrade" dependency versions, but they all involve changing what is in the go.mod / go.sum file. The references need to be stable. As far as I know there is no "semver"-trick you can do like in a package.json of NodeJS.

So, I don't think there is a simple command that will do this automatically as the Go developers seem to favor reproducibility and stability over simplistic upgrades. (These are good reasons too, in my view, given the tasks that Go was made to solve)

As an example, you should be able to list available upgrades with:

go list -m -u all

My suggestion is to use a GitHub action to "vet" the dependencies using the go tools and some scripting, and maybe automatically add a GitHub issue if there is a big enough version bump in a dependency. It would not surprise me if someone somewhere have already made a tool for this and open-sourced it. As with almost anything else...