Background

Starting this fiscal year (FY2018-19), Readers Web are introducing the Advanced Mobile Contributions mode to the mobile site (herein "AMC"; see T198313: [GOAL] Advanced mobile contributions for the rationale, a high-level overview of the project, and links to on-wiki documentation). Like the beta mobile mode, users will have to opt-in to AMC mode but note well that users can opt into either mode independently.

During discussions around T210653: [EPIC] AMC - Opting in and in T211195: [Spike 16hrs] Investigate opt-in audience and instrumentation Readers Web decided that the complexity of allowing logged out users to opt into AMC was such that it should be de-scoped until they've shipped a set of AMC features.

One aspect of the complexity of allowing logged out users to opt into AMC is how we can deliver different HTML and assets to the UA:

In T211195: [Spike 16hrs] Investigate opt-in audience and instrumentation, @pmiazga noted that if you've opted into mobile beta mode, then you'll always miss the edge caches. Per T182235#4752852, this isn't too worrisome, as mobile beta mode pageviews constitute ~0.5% of all mobile pageviews.

Should the edge caches behave the same way for users who've opted into AMC?

Considerations

• Missing the edge caches incurs a performance penalty which may bias a user's perception of the AMC, should we serve these requests from the edge caches?
  • Do we know what performance penalty a logged in mobile site user incurs?
• Readers Web can't estimate how many logged out users would opt in, so we can't be sure about what pressure we'd put on the edge caches
• Readers Web are generally unsure of SRE/Traffic's feeling towards splitting the edge caches