What do you consider as a big web application
What's your personal metric, to consider a web application as big and complex ? Is it the number of models, or background processing logic. Or for those in the micro-services camp, is it the number of services. Or something else entirely
I've been building a Django web project for a while now, it has several modules, started out with two, now it has around 5. But that's not the point, right? It kind of is. A simple project with a dozen modules within it can be complex in terms of memory usage whereas a single app that performs various asynchronous tasks can be complex in terms of CPU usage.
What I'm trying to say here is that everyone's metric differs on what a complex application. To me and probably a lot of people, a web app getting 10000 requests a day is small-scale but along the upper lines of small scale and can be considered medium scale if it's something along the line of a web application like a video hosting service that just took off. Time since the site is up also matters.
And yeah, both the number of models and background processing logic matters in defining a complex application. Refer to my first paragraph.
As for microservices, the more clusters you have, the more complex your service gets and the more the database get requests ( GET, POST, PUT, DELETE ), the more your project would need to scale.
In conclusion, the complexity of an application depends on CPU Usage ( having to use 2 VCPUs with 16 Gb of ram within a month of usage by 10000 people daily is a rough idea of what complex could look like but there is really no definition that defines where complex starts, a lot of factors matter ), Memory Usage, Database usage, Data Transfer and more.
Everything you mentioned, and how long it takes to pinpoint how a particular thing (route/controller) works when something breaks. Also any monolith is usually "big" enough for me.