We're going to need a server somewhere. There are thousands of providers out there, but these are the three that I personally recommend. I'm not going to go over the details of how to get started with them, because that's out of the scope of this book. Instead I'll talk about their benefits with regards to hosting Flask applications.
13.1.1. Amazon Web Services EC2
Amazon Web Services is a collection of services provided by ... Amazon! There's a good chance that you've heard of them before as they're probably the most popular choice for new startups these days. The AWS service that we're most concerned with here is EC2, or Elastic Compute Cloud. The big selling point of EC2 is that we get virtual servers - or instances as they're called in AWS parlance - that spin up in seconds. If we need to scale our app quickly it's just a matter of spinning up a few more EC2 instances for our app and sticking them behind a load balancer (we can even use the AWS Elastic Load Balancer).
With regards to Flask, AWS is just a regular old virtual server. We can spin it up with our favorite linux distro and install our Flask app and our server stack without much overhead. It means that we're going to need a certain amount of systems administration knowledge though.
13.1.2. Heroku
Heroku is an application hosting service that is built on top of AWS services like EC2. They let us take advantage of the convenience of EC2 without the requisite systems administration experience.
With Heroku, we deploy our application with a git push to their
server. This is really convenient when we don't want to spend our time
SSHing into a server, installing and configuring software and coming up
with a sane deployment procedure. This convenience comes at a price of
course, though both AWS and Heroku offer a certain amount of free
service.
Note Heroku has a tutorial on deploying Flask with their service.
Note Administrating your own databases can be time consuming and doing it well requires some experience. It's great to learn about database administration by doing it yourself for your side projects, but sometimes you'd like to save time and effort by outsourcing that part to professionals.
Both Heroku and AWS have database management offerings. I don't have personal experience with either yet, but I've heard great things. It's worth considering if you want to make sure your data is being secured and backed-up without having to do it yourself.
13.1.3. Digital Ocean
Digital Ocean is an EC2 competitor that has recently begun to take off. Like EC2, Digital Ocean lets us spin up virtual servers - now called droplets - quickly. All droplets run on SSDs, which isn't something we get at the lower levels of EC2. The biggest selling point for me personally is an interface that is far simpler and easier to use than the AWS control panel. Digital Ocean is my preference for hosting and I recommend that you take a look at them.
The Flask deployment experience on Digital Ocean is roughly the same as on EC2. We're starting with a clean linux distribution and installing our server stack from there.
Note Digital Ocean was nice enough to make a contribution to the Kickstarter campaign for Explore Flask. With that said, I promise that my recommendation comes from my own experience as a user. If I didn't like them, I wouldn't have asked them to pledge in the first place.