Install latest rustc/cargo where needed

The cryptography Python package requires rustc >= 1.65.0 to build
now, and Debian only comes with 1.63.0 by default. We therefore
utilize the rustup installation script, similar to the get-pip.py
script, to get the latest version for the architectures where this
build step is needed.

In the Alpine case we never need to build the package, so remove
the rust dependency there.

In the case of i386 the rustup script is unable to correctly identify
which system it is to build for, so we need to provide this info
manually.

src/Dockerfile

@@ -24,6 +24,10 @@ ENV CERTBOT_DNS_AUTHENTICATORS \
 # any real need to cater to other programs/environments.
 ARG PIP_BREAK_SYSTEM_PACKAGES=1
 
+# We need to do some platfrom specific workarounds in the build script, so bring
+# this information in to the build environment.
+ARG TARGETPLATFORM
+
 # Through this we gain the ability to handle certbot upgrades through
 # dependabot pull requests.
 COPY requirements.txt /requirements.txt
@@ -34,7 +38,6 @@ RUN set -ex && \
     apt-get update && \
     apt-get install -y --no-install-recommends \
             build-essential \
-            cargo \
             curl \
             libffi8 \
             libffi-dev \
@@ -45,6 +48,18 @@ RUN set -ex && \
             python3 \
             python3-dev \
     && \
+# Install the latest version of rustc/cargo if we are in an architecture that
+# needs to build the cryptography Python package.
+    if echo "$TARGETPLATFORM" | grep -E -q '^(linux/386|linux/arm64|linux/arm/v7)'; then \
+        curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | /bin/sh -s -- -y \
+# For some reason the rustup script is unable to correctly identify the
+# environment if we are building an i386 image on an x86_64 system, so we need
+# to provide this information manually.
+        $(if [ "$TARGETPLATFORM" = "linux/386" ]; then \
+            echo "--default-host i686-unknown-linux-gnu"; \
+        fi) && \
+        . "$HOME/.cargo/env"; \
+    fi && \
 # Install the latest version of PIP, Setuptools and Wheel.
     curl -L 'https://bootstrap.pypa.io/get-pip.py' | python3 && \
 # Install certbot.
@@ -54,18 +69,19 @@ RUN set -ex && \
 # Remove everything that is no longer necessary.
     apt-get remove --purge -y \
             build-essential \
-            cargo \
             curl \
             libffi-dev \
             libssl-dev \
             pkg-config \
             python3-dev \
     && \
+    if echo "$TARGETPLATFORM" | grep -E -q '^(linux/386|linux/arm64|linux/arm/v7)'; then \
+        rustup self uninstall -y; \
+    fi && \
     apt-get autoremove -y && \
     apt-get clean && \
     rm -rf /var/lib/apt/lists/* && \
     rm -rf /root/.cache && \
-    rm -rf /root/.cargo && \
 # Create new directories and set correct permissions.
     mkdir -p /var/www/letsencrypt && \
     mkdir -p /etc/nginx/user_conf.d && \

src/Dockerfile-alpine

@@ -33,7 +33,6 @@ RUN set -ex && \
 # Install packages necessary during the build phase (for all architectures).
     apk add --no-cache \
         bash \
-        cargo \
         curl \
         findutils \
         libffi \
@@ -54,14 +53,12 @@ RUN set -ex && \
     pip3 install $(echo $CERTBOT_DNS_AUTHENTICATORS | sed 's/\(^\| \)/\1certbot-dns-/g') && \
 # Remove everything that is no longer necessary.
     apk del \
-        cargo \
         curl \
         libffi-dev \
         libressl-dev \
         python3-dev \
     && \
     rm -rf /root/.cache && \
-    rm -rf /root/.cargo && \
 # Create new directories and set correct permissions.
     mkdir -p /var/www/letsencrypt && \
     mkdir -p /etc/nginx/user_conf.d && \