Use apk --no-cache' instead of --update'

[mcornella]

This avoids the need to do rm -rf /var/cache/apk. Needs alpine ≥ 3.3.
See https://github.com/gliderlabs/docker-alpine/blob/f93486d/docs/usage.md#disabling-cache

Here's an example diff between running apk --no-cache add tar and apk --update add tar:

$ diff <(docker diff e1ce7fc8b230 | sort) <(docker diff 4f4bb52532e5 | sort)         
3a4,5
> A /var/cache/apk/APKINDEX.5a59b88b.tar.gz
> A /var/cache/apk/APKINDEX.7c1f02d6.tar.gz
16a19,21
> C /var
> C /var/cache
> C /var/cache/apk

Thanks so much, you rock! 😄

[jessfraz]

Thanks ya some of mine in my dockerfiles repo do this and some don't because of when they were written, if you get bored :)

[mcornella]

Thanks ya some of mine in my dockerfiles repo do this and some don't because of when they were written, if you get bored :)

Yep, I've seen your dockerfiles, for once. If you don't mind losing the docker layer reuse optimization, I'll gladly fix some of those.

Thanks again!