Build static binaries for Docker, so that we can use 'scratch' image

[ylebre]

This should fix issue #1765

[update-docs]

Thanks for opening this pull request! The maintainers of this repository would appreciate it if you would create a changelog item based on your changes.

[IljaN]

There could be dragons, see owncloud/ocis#375

[ishank011]

@SamuAlfageme can you take a look?

[michielbdejong]

I'm trying this out in cs3org/ocm-test-suite#27.
So far it works, but I must say the new very slim image is hard to debug, for instance:

docker run -it --entrypoint /bin/sh revad

fails because there is no /bin/sh.

[SamuAlfageme]

@ylebre great catch, I did forget to set the CGO_ENABLED variable on the ENVs builder step from the Dockerfile(s).

@IljaN I'll also review what cgo dependencies are we still using and how can we avoid them if that is the case.

[SamuAlfageme]

@michielbdejong I totally empathize. Using the binary FROM scratch is great to reduce the attack surface and size of the image, but can make debugging inside the container very cumbersome.

I have used this scratch-debugger script in the past. But if you're developing locally, I'll recommend you create an image with your OS of choice as base and then copying the revad binary --from the cs3org/revad image.

In the future, things like ephemeral containers in k8s kubernetes/enhancements#277 will make that task easier.

We can also reconsider using busybox or alpine if this becomes too annoying in the future

[SamuAlfageme]

@ylebre could you add a changelog entry for your fix?

[ylebre]

@SamuAlfageme sure thing, added to the PR now.

[SamuAlfageme]

@ylebre thx a bunch!