Actually I never tried but I was scared by the small print of GH not using RDS themselves [1] and Ghost relying on lower-level features that might be not easily available in RDS. Also I had the impression you have to setup a normal non-RDS replica attached to your RDS master?
At my previous employer we've run it just fine from an EC2 instance talking to a MySQL RDS database. At some point the triggers from pt-osc were really hurting when trying to migrate big (several billion rows) table with heavy traffic and gh-ost really helped with that. That said, gh-ost is definitely a big boy tool and it took us a few tries to get the settings just right. No downtime or anything, we just had to delete the new table and start over. Still annoying when it wastes several hours :)
GH no longer uses RDS. They had some services which relied on that maybe 3 years ago. Migrations were performed with gh-ost, but if not running replicas (RDS was not) it would downgrade to mysql binaries
GH is migrating from gh-ost in general, as it’s not even used in the enterprise products (though GitHub.com relies on it, the next iteration will phase it out)
That's true. However, if you don't already have any "traditional" (binlog-based) replicas on Aurora, you might not even need gh-ost or pt-osc in the first place -- at least for many common ALTER operations.
Aurora supports physical replication at the storage level, which means you can use MySQL online DDL (ALGORITHM=INPLACE, LOCK=NONE) without having to worry about replication lag. Recent blog post with findings from Percona: https://www.percona.com/blog/zero-impact-on-index-creation-w...
Caveats:
* This is safe on Aurora 3 due to MySQL 8's atomic DDL support. On previous versions, there may be crash-safety risks, which make external tools safer for altering very large tables.
* External OSC tools can provide other advantages, such as throttling, safer to cancel, ability to time the final table switchover, ability to rollback (pt-osc supports "reverse" triggers), etc.
* Some forms of ALTER TABLE don't support online DDL, and for those you'd still need an external OSC tool like gh-ost or pt-osc, but it's less common.
[1] https://github.com/github/gh-ost/blob/master/doc/rds.md