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- [Narrator] Hi and
welcome back to the course.

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In this video we're going to look at

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what exactly is Heroku and how it works.

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Heroku, as I've mentioned,
is a web service

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that runs your code and
allows other people to see it.

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So you can give it your Flask applications

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and it can run your Flask apps,

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and it makes them available
for others to interact with.

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When you run the Flask
app in your computer,

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other people can't access it,
log in, and make requests.

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However, when you run them on Heroku,

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other people can do that because Heroku

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gives them a URL and address
that others can access.

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Generally, allowing
that, giving other people

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a URL that they can access,

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is called hosting,
essentially, so you can host,

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for example, word press sites,
you can host Flask apps,

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you can host static websites, etc.

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Heroku can be used to
host Flask applications.

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It can also be used to
host many other things,

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so you're not limited to just that.

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It can host Ruby apps,
it can host Go apps, etc.

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Heroku works with dynos,

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and this here a picture of
a dyno, and what a dyno is

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is very similar to a server.

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A server is something
that can put your code on,

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and then run your code
and make it available

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for other people, and a dyno
does exactly the same thing.

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A dyno is Heroku's version of a server.

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However, it's not quite a computer.

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It is something called a virtual machine.

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So when you run your application,

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you application doesn't have control

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of the computer in which it is running.

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It only has control of the virtual system

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that has been created
specifically for that dyno.

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Now that means that there
are a couple of limitations

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in terms of what we can do.

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And also, because when we
use a dyno, we tell Heroku

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what Flask application to
run, and then it does that.

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We're limited also in running
other things simultaneously.

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For example, something
we might be interested

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in running simultaneously
alongside our Flask app

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is a way of improving
performance of our app

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by adding a caching layer.

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We cannot do that in Heroku, for example.

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However, what we can do
is we can tell Heroku

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to run our Python our app,

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and also we will have to tell it

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to run something called uWSGI.

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UWSGI is a way of

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serving your flask application.

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Although the Flask application
has a serving layer,

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that's how we access it using
postman or our web server.

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It's not the best, and also it is limited

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in what it can interact with.

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By running uWSGI, which is
another Python library, on top,

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we're going to make our Flask
app a lot more flexible.

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We're going to look at
exactly what that means

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and how to do all this

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in the coming videos.

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Okay, so this is what
our dyno is going to run.

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It's going to run the
Python app, the Flask app,

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which includes Flask-RESTful
and Flask-SQLAlchemy and so on,

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and it's also going to run uWSGI.

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The uWSGI app or library
is going to interact

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with our Flask app in
order to make it available

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for others to use.

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So our Heroku app is going to
look essentially like this.

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We're gonna have a big box,
which is our Heroku app,

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and that is going to be
composed of a single dyno.

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The Heroku app in addition
can also have other things

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such as configuration properties.

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For example, we can configure
what database we want to use.

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We can use SQLite, we can
also use Postgres from iSQL.

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We can also configure things
like where the logs appear.

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Whenever our application
crashes, we can put some logging,

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some printing out to
the console somewhere.

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We can decide where that
is, we can do things like

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setting up a bunch of other
configuration parameters.

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And in addition, the
Heroku apps are not limited

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to just limited to running a single dyno,

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but they can also run many
other dynos a the same time.

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As you can see all these dynos
run exactly the same code,

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and that means that for
example, as an example,

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each dyno can deal with one
user, if we run six dynos

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we can deal with six users simultaneously.

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This is a bit of an oversimplification,

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don't worry, each dyno
can deal with many users,

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but of course if you have six,

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that's six times more users you
can deal with, more or less.

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All of these dynos can interact
with the same database,

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so data can be shared between them,

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and overall, this
increased number of dynos

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would just make your app go
faster and be more available.

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However, you will have to pay if you want

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to increase the number of dynos,

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so that's a limitation there.

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Also, Heroku is great for security

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because Heroku enables
Secure Sockets Layer for us,

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so we don't have to do anything.

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SSL is automatically enabled,

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and what SSL does is it
allows the communication

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between yourself, the
client, and the server,

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which is Heroku, to be encrypted,

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so all of your users, all
of your REST API users,

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are going to see encrypted communication

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going to the server, which
is great, for example,

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when we're sending passwords
and things like that.

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That's just so nobody else
can snoop on that information

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and read it if it is encrypted.

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So as a conclusion, Heroku is
a distributed hosting service,

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which means each dyno is
separate from the others.

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And each server is called a dyno,

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and it runs your application.

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And also, the free tier
gives you one dyno,

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which is what I mentioned earlier,

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but you have limited running hours,

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so you cannot run the dyno continuously.

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It goes to sleep every now and then,

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and then it takes a few
seconds to start up again,

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so we'll look into exactly what that means

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in the next few videos.

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And also its got a good security profile

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due to SSL being enabled by default.

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So that's it for this video,

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a quick intro to what Heroku
is and how it's gonna run,

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and now we're gonna work on
deploying our app to Heroku.

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I'll see you in the next video.