Docker build fails due to cryptography dependency

[mattforscale]

Docker build fails when trying to install cryptography on Raspberry Pi 4. The suggested workaround of adding CRYPTOGRAPHY_DONT_BUILD_RUST=1 to the Dockerfile works, and I haven't experienced any issues.

=============================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If you are using an outdated pip version, it is possible a prebuilt wheel is available for this package but pip is not able to install from it.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

[mik3y]

Resolved in #420, also resolved again (differently; sigh) in #426.