We need to ramp-up usage of php7 to 100% both on the appserver and the API cluster.
This means progressively changing the sampling rate on both clusters to 5,10, 20, 50 and 100%.
For the API cluster, we will convert each API server to serve only via php7.2-fpm. Each API server serves ~2% of traffic.
Once that's done, and we're confident we won't need to revert, we will need to cleanup:
* Remove the conditional in the virtual hosts, send all requests to php by default.
* Remove all the code from the WikimediaEvents extension that sets the cookie for this transition
* Remove any code in apache/varnish that does set the cookie for API requests
Record of going live for appservers:
| Level | Went live | Git change |
| ----- | --------- | ---------- |
| 0.1% | 2019.03.25 | 5a270bbebf |
| 1% | 2019.04.30 | 88984d4d20 |
| 5% | 2019.05.02 | 8afada66e1 |
Record of going live for API cluster: