Where does web server come into play in OpenStack - CloudFoundry stack

You would generally not deploy OpenStack on top of AWS. OpenStack is similar to AWS in that it provides a service for you to create and destroy virtual machine instances, manage networking between and around your VMs, attach and detach block devices to instances, etc. In other words, both are services for managing "infrastructures", where "infrastructure" here means a virtualized datacenter, which at its core means a bunch of hardware running hypervisors that allow you regard the datacenter as a bunch of virtual machines that can be spun up and down on demand, rather than a bunch of "static" physical machines.

AWS is an Infrastructure-as-a-Service provided by Amazon, so you don't have to install AWS yourself, you can just start using it to provision VM instances within Amazon's datacenters. OpenStack is software you install yourself (or pay a vendor to manage for you) on hardware you own or pay for yourself, and once installed OpenStack provides a similar service/interface to AWS.

With a Platform-as-a-Service, you concern yourself more with your application code, and "just pushing it", and don't have to concern yourself as much with what's happening on the underlying machine. You don't have to worry as much about the underlying OS, making sure you have the right runtime and code dependencies of your application, generally don't have to care about the webserver that's serving your code, etc. And you get many more higher level features, e.g. easy ability to scale vertically or horizontally, dynamic routing, automatic log aggregation, automatic health management, etc.

As far as how nginx fits in, it depends how you're using nginx, and what kind of application you have. Cloud Foundry has few couple ways of dealing with applications.

One is the buildpack model, where you simply push your source code to the platform, and it will automatically detect the appropriate runtime and dependencies for your application. For instance, if your application is a Ruby application, it will automatically detect this, and by default automatically run the application using the WEBrick server. However, you can choose other Ruby webservers such as Phusion, Passenger, etc. [1]

If your application is primarily serving static content, it will use nginx as the webserver. [2]

Another is using Docker. You can deploy applications based on Docker images on Cloud Foundry, in which case you could have a container running nginx and your application inside the container, or not, it depends on whether you still need nginx. Pushing a docker application is as simple as:

cf push trainingwebapp --docker-image training/webapp -c 'python app.py'

Here, this uses the sample Hello World web app from the Docker documentation. [3]

[1] https://docs.cloudfoundry.org/buildpacks/ruby/ruby-prod-server.html
[2] https://docs.cloudfoundry.org/buildpacks/staticfile/index.html
[3] https://docs.docker.com/engine/userguide/containers/usingdocker/