Alpine base image version

[lukebakken]

With regard to #592

Why is alpine:3.17 used and not alpine:3?

[tianon]

The build failures you're seeing on #589 are a great example -- it's the same as why we wouldn't pin to debian:latest or ubuntu:latest; we want to control when we do those stable updates to make sure that everything actually works correctly (and sometimes there are deeper concerns with distro upgrades, like docker-library/postgres#582).

[lukebakken]

Thanks