- The GitHub API and its code load endpoints are not reachable via IPv6, making it impossible to download release artefacts from many projects, lots of which distribute their software via GitHub exclusively (Prometheus for instance).
- The default Ubuntu key servers aren't reachable via IPv6, making it difficult to install packages from third-party registries, such as Docker or Grafana. While debugging, I noticed huge swaths of the GPG infrastructure are defunct: There aren't many key servers left at all, and the only one I found actually working via IPv6 was pgpkeys.eu.
- BitBucket cannot deploy to IPv6 hosts, as pipelines don't support IPv6 at all. You can self-host a pipeline runner and connect to it via v6, BUT it needs to have a dual stack - otherwise the runner won't start.
- Hetzner itself doesn't even provide their own API via IPv6 (which we talk to for in-cluster service discovery. Oh, the irony.