Using external caches?
This is rather a documentation than a software issue, but the wiki didn't let me write to the discussion page of the apk management.
When creating virtual images (especially with docker) with alpine (what it is just perfect for), it takes typically lots of iterations to recreate the image and have lots of apk packages installed from scratch. Since every installation run typically starts with a fresh, clean system without a persistent cache dir, there is no point in using the local cache feature of apk.
Fetching the images again with every run is time consuming, creates network traffic (possibly expensive), and puts load on alpine's servers. So there's good reason to try to have some local mirror/cache. Unfortunately I didn't find any hint in the docs on what's the recommended way. They are just mentioning apk's local cache function.
Other package managers like apt, yum, gem allow to configure external caches/proxies.
My guess (not yet tested) would be hat apk should honor a https_proxy environment variable pointing to an external, HTTPS-intercepting cache after installing it's certificate to /etc/ssl/certs, but I didn't try this yet.
It would therefore be good to have a section in the documentation about how to use apk with some external cache mechanism.