Once the "next" deployments of these services take shape (T377040) we'll need to add support for progressively routing external traffic to them.
There are two parts to this:
- We will need to develop an ATS Lua plugin script for remapping the "main" deployment target (e.g., mw-web, mw-web-ro) to the respective "next" target (e.g., mw-web-next, mw-web-next-ro) depending on the presence / value of the cookie.
- We will need to revive support for consistent fractional cookie enrollment via the WikimediaEvents extension (see e.g. [0] previously used in the migration to 7.4).
One important aspect to #1 is also supporting a "load fraction" that routing to "next" is predicated upon in addition to the cookie. This allows us to incrementally shift traffic back to "main" once it's fully updated to 8.1 during the final phase of the migration, in a way that's independent of migration cookie state (aside: we could also use this in a similar way in the very unlikely event of an emergency where we need to shunt back to 7.4 in a semi-controlled way).