Add root certificates to a Debian container

I supposed this is potentially a problem with many images, but it definitely is with Debian (at least, as of December 2022): Debian Docker images don’t install the package ca-certificates by default, which means any network requests that use TLS will fail with an error that looks something like this:

x509: certificate signed by unknown authority

The fix is pretty simple: just install the ca-certificates package, which adds root certificates so the OS can verify signatures.

apt install -y ca-certificates

That’s the shell command to install the package. In a Dockerfile, it should probably look something like this:

RUN apt-get update
RUN apt install -y ca-certificates