This is a tracker task to figure out testing / qa needs and any work / changes needed to VisualEditor to switchover from Parsoid/JS to Parsoid/PHP.
T229015: Tracking: Direct live production traffic at Parsoid/PHP is the tracker task for deployment. But, we don't anticipate a deploy before mid-September 2019 at this time. But, let us handle this as if we are going to be switching over Flow to Parsoid/PHP around end September / early October.
Since Flow does not talk to RESTBase, Flow would need a config change to update its endpoints. At this time, we are planning to switch Parsoid clients one at a time. Currently, we are considering switching over Flow as the last Parsoid client. We are assuming we will have all the bugs ironed out by that time and can do a simple switchover without needing traffic partitioning. But, if it becomes necessary, Flow will need to manage a new cookie.
While Flow's HTML storage has data-parsoid DSR offsets stored there, since Flow does not use selective serialization, these offsets are ignored by Parsoid. Nevertheless, it might be appropriate to null out the old offsets (or have some suitable protection against future use) since the offsets generated by Parsoid/JS code are invalid in Parsoid/PHP land.
We will also do an early deployment to the beta cluster so that clients can do early testing there. However, Flow will nevertheless need some update / code to pick its endpoint on the Beta cluster.
But, please comment on the ticket / edit the description adding any other requirements to ensure we cover all our bases.