Unable to install cryptograpy package in python, since it requires rust

The python package cryptography requires rust nowadays. The Alpine image that is used by faas-cli doesn't contain rust. This causes the building of the docker image to fail.

More info: https://github.com/pyca/cryptography/issues/5771

Note that an older version of the cryptography package also doesn't work, due to the dependency on libssl-dev.

It would be nice if both of these were available, at the very least if the dev build-option is enabled.

Expected Behaviour

The docker image builds successfully

Current Behaviour

I'm getting the error:

running build_rust

      =============================DEBUG ASSISTANCE=============================
      If you are seeing a compilation error please try the following steps to
      successfully install cryptography:
      1) Upgrade to the latest pip and try again. This will fix errors for most
         users. See: https://pip.pypa.io/en/stable/installing/#upgrading-pip
      2) Read https://cryptography.io/en/latest/installation.html for specific
         instructions for your platform.
      3) Check our frequently asked questions for more information:
         https://cryptography.io/en/latest/faq.html
      4) Ensure you have a recent Rust toolchain installed:
         https://cryptography.io/en/latest/installation.html#rust
      5) If you are experiencing issues with Rust for *this release only* you may
         set the environment variable `CRYPTOGRAPHY_DONT_BUILD_RUST=1`.
      =============================DEBUG ASSISTANCE=============================

  error: can't find Rust compiler

  If you are using an outdated pip version, it is possible a prebuilt wheel is available for this package but pip is not able to install from it. Installing from the wheel would avoid the need for a Rust compiler.

  To update pip, run:

      pip install --upgrade pip

  and then retry package installation.

  If you did intend to build this package from source, try installing a Rust compiler from your system package manager and ensure it is on the PATH during installation. Alternatively, rustup (available at https://rustup.rs) is the recommended way to download and update the Rust compiler toolchain.

  This package requires Rust >=1.41.0.
  ----------------------------------------
  ERROR: Failed building wheel for cryptography

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List All Possible Solutions and Workarounds

The github issue suggests either this:

sudo apk add gcc musl-dev python3-dev libffi-dev openssl-dev cargo

Or this:

pip install --upgrade pip

Steps to Reproduce (for bugs)

Make a python3 function
Add the cryptography package to the requirements.txt (I used version 3.4.7)
build the function with faas-cli

Context

This issue prevents me from building my function, so I can't deploy it.

Your Environment

FaaS-CLI version ( Full output from: faas-cli version ): 0.13.9
Docker version ( Full output from: docker version ): 20.10.1
Are you using Docker Swarm (FaaS-swarm ) or Kubernetes (FaaS-netes): kubernetes (1.18.10)
Operating System and version (e.g. Linux, Windows, MacOS): WSL2 on windows 10 (version 2004)
Link to your project or a code example to reproduce issue: private repo, sorry.

openfaas / templates