While for users connecting with a browser (and their API requests) will go to PHP7 directly, we need to find a way to send a percentage of cookieless API traffic to PHP7 instead than HHVM.
I can think of two places where this can be done:
- At the edge
- In apache
Lastly, we decided not to separate varnish caches
- php72_only apache feature flag https://gerrit.wikimedia.org/r/513273
- enable on mw2135 https://gerrit.wikimedia.org/r/513277
- enable on mw1348 https://gerrit.wikimedia.org/r/513277
This method might be added to internal calls as well.