When running Nix inside of a container image, there are several
environment-specific details that need to be configured appropriately.
Most importantly, since one of the recent Nix 2.x releases, sandboxing
during builds is enabled by default. This, however, requires kernel
privileges which commonly aren't available to containers.
Nixery's demo instance (for instance, hehe) is deployed on AppEngine
where this type of container configuration is difficult, hence this
change.
Specifically the following were changed:
* additional tools (such as tar/gzip) were introduced into the image
because the builtins-toolset in Nix does not reference these tools
via their store paths, which leads to them not being included
automatically
* Nix sandboxing was disabled in the container image
* the users/groups required by Nix were added to the container setup.
Note that these are being configured manually instead of via the
tools from the 'shadow'-package, because the latter requires some
user information (such as root) to be present already, which is not
the case inside of the container
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