I'm struggling with the decision between a traditional backend (let's say a Django instance managing everything) and a service oriented architecture for a web app resembling LinkedIn. What I mean with SOA is having a completely independent data access interface - let's say Ruby + Sinatra - that queries the database, an independent chat application - Twisted - which is used via its API, a Django web server that uses those APIs for serving the content, etc.
I can see the advantages of having everything in the project modularized and accesed only via APIs: scalability, testing, etc. However, wouldn't this undermine the site performance? I imagine all modules would communicate via HTTP requests so wouldn't this arquitecture add a lot of latency to basically everything in the site? Is there a better alternative than HTTP?
Secondly, regarding development ease, would this really add much complexity to our developers? Specially during the first phase until we get an MVP.
Edit: We're a small team of two devs and a designer but we have no deadlines so we can handle a bit of extra work if it brings more technical value
Short answer, yes, SOA definitely trades encapsulation and reusability for latency. Long answer, it depends (as it always does) on how you do it.
How much latency affects your application is directly proportional to how fine-grained your services are. If you make very fine-grained services, you will have to make hundreds of sequential calls to assemble a user experience. If you make extremely coarse-grained services, you will not get any reusability out of your services; as they will be too tightly coupled to your application.
There are alternatives to HTTP, but if you are going to use something customized, you need to ask yourself, why are you using services at all? Why don't you just use libraries, and avoid the network layer completely?
You are definitely adding costs and complexities to your project by starting with an API. This has to balanced by the flexibility an API gives you. It might be a situation where you would benefit from internally structuring APIs to your code-base, but just invoking them as modules. Or building libraries instead of stand-alone APIs.
A lot of this depends on how big your project is. Are you a team of 1-3 devs cranking to get out your MVP? Or are you an enterprise with 20-100 devs that all need to figure out a way to divide up a project without stepping on each other?