[threeseed]

Ad serving and metrics are asynchronous so won't block any UI. And authentication/identity has the same behaviour with monolith/microservices. It's ultimately just a look up this user in some database.

It's the serving of the content that requires coordination across multiple services and most of that should be cached at the serving layer.

[felixgallo]

Incorrect, in most apps nontrivial content is highly personalized and dynamically served, auth in microservices is frequently two or more hop rather than one hop, and ad serving and metrics frequently involve synchronous steps.