Odoo server contains all of the enterprise logic and ensures that Odoo runs optimally. One layer of the server is dedicated to communicate and interface with the PostgreSQL database, the ORM engine. Another layer allows communications between the server and a web browser, the Web layer. Having more than one server is possible, for example in conjunction with a load balancing mechanism.
Odoo provides an application server on which specific business applications can be built. It is also a complete development framework, offering a range of features to write those applications. The OpenERP server also features a specific layer designed to communicate with the web browser-based client. This layer connects users using standard browsers to the server.
From a developer perspective, the server acts both as a library which brings the above benefits while hiding the low-level details, and as a simple way to install, configure and run the written applications. The server also contains other services, such as extensible data models and view, workflow engine or reports engine. However, those are OpenERP services not specifically related to security and are therefore not discussed in detail in this document.
Latest Odoo server compatible to your OS and add-ons will be installed on your AWS EC2 server. Odoo version can vary in case any compatibility issue comes up with latest available Odoo version.