Update minimal dockerfiles to use multi-stage builds to achieve minimalness

[cyli]

cc @endophage @justincormack

[riyazdf]

LGTM

[justincormack]

that meant ln ie the symlink

[justincormack]

and here

[justincormack]

looks fine bar comment about comment but needs a rebase.

[cyli]

Thanks @justincormack! Fixed.

[thaJeztah]

If "tiny-ness" is important; use --no-cache instead;

docker build -t before -<<EOF
FROM golang:1.9.4-alpine AS build-env
RUN apk add --update git gcc libc-dev
EOF

docker build -t after -<<EOF
FROM golang:1.9.4-alpine AS build-env
RUN apk add --no-cache git gcc libc-dev
EOF

REPOSITORY      CREATED                  SIZE
after           Less than a second ago   386MB
before          Less than a second ago   387MB

[cyli]

This is using a build image and a final image, though - does the no-cache affect the final image? This is the before and after image built with the server.minimal.Dockerfile, without the --no-cache option and with the --no-cache option:

REPOSITORY                                       TAG                    IMAGE ID            CREATED              SIZE
<none>                                           <none>                 fa5c316b8562        17 seconds ago       540MB
after                                            latest                 f3f0621261c3        About a minute ago   21.1MB
before                                           latest                 f3f0621261c3        About a minute ago   21.1MB
<none>                                           <none>                 82a30458273b        About a minute ago   540MB

[thaJeztah]

No it doesn't affect the final image (but does affect your local cache 😅); it was mainly a nit, and I wanted to mention --no-cache because it's awesome: it takes care of everything (updating the index, and removing it afterwards)

[cyli]

Oh nice! It seems to only be a MB or less, so in this case it seems ok, but I will keep that in mind for all my other images!