RSA key not supported on Ubuntu 22.04 LTS server anymore, clients fail to Git clone with SSH protocol

Problem to solve

Ubuntu 22.04 LTS provides OpenSSH in a new version that removes support for RSA keys. This affects git clone operations that use SSH keys with GitLab running on Ubuntu 22.04 LTS.

I've also seen the problem with creating a new VM based on Ubuntu 22, and trying to use SSH and ssh-copy-id.

Further details

The solution was to delete the RSA key, and re-create the key using a modern recommended alternative.

ssh-keygen -t ed25519 -C "me@mymachine"

Proposal

  1. Deprecate RSA keys to use with GitLab https://docs.gitlab.com/ee/user/ssh.html#supported-ssh-key-types
  2. Update the docs with troubleshooting help in https://docs.gitlab.com/ee/user/ssh.html
  3. Verify other areas that use SSH keys (Git commit signing)

Who can address the issue

groupdistribution for deprecating RSA keys thoughts. Troubleshooting needs to document that SSH clones with a RSA key and Ubuntu 22.04LTS server won't work.

I'm not sure if that problems affects signing Git commits with SSH keys. cc @bwill

Other links/references