Investigate: Gitlab registry push extremely slow with Kaniko

My upload speed trying to push to the gitlab registry is extremely slow. Speed uploading to any other resource can go up to 7 mb/s, speedtests show around 60 Mbps upload speeds, however pushing to the gitlab registry only gets around 100 - 150 kb/s upload speed.

See #241996 (comment 1539372826) for reproducing this issue.

Workaround

Make kaniko use HTTP/1.1 by setting the env variable GODEBUG="http2client=0" in the kaniko container.

https://docs.gitlab.com/ee/user/packages/container_registry/troubleshoot_container_registry.html#slow-uploads-when-using-kaniko-to-push-large-images