As I described in the MR, it has been incorrect since January 2018. For 50 months.
As gitlab-shell!181 (merged) removed connection between GitLab Shell and Redis since 2018, !80083 (merged) (by @sunjungp) should be updated as so.
This is the full architecture diagram (as of April XX, 2022). This is too complicated for developers (or external contributors so-called as GitLab wider community contributors).
https://www.google.com/search?tbm=isch&q=gitlab+architecture (Image search of "gitlab architecture") will not be updated soon as updated on Git as you can see:
Thanks @sunjungp (Sunjung Park for clarifying the problem and resolving it sooner.
After its IPO of GitLab (company), GitLab (team) will still need more numbers of wider community contributions in code. To get code contributions from the wider community, GitLab team (and GitLab core) needs to pay attentions to make new and old developers understand its architecture, which has become heavily complicated for 10 years.