In our Hands-On section, we show how to deploy a deployable image file using Flyctl. Now we are going to deploy an application from source. In this Getting Started article, we look at how to deploy a Python application on Fly.
You can get the code for the example from the Fly-Examples Github repository. Just git clone https://github.com/fly-examples/python-hellofly-flask to get a local copy.
The Python hellofly application is, as you'd expect for an example, small. It's a Python application that uses the Flask web framework. Here's all the code form hellofly.py:
from flask import Flask, render_template
app = Flask(__name__)
@app.route('/')
@app.route('/<name>')
def hello(name=None):
return render_template('hello.html', name=name)Flask is set up to route request to a hello function which in turn passes a name value (taken from the requests path)to a function to render a template. The template resides in the templates directory under the name hello.html. It too is very simple too:
<!DOCTYPE html>
<html lang="en">
<head>
</head>
<body>
<h1>Hello from Fly</h1>
{% if name %}
<h2>and hello to {{name}}</h2>
{% endif %}
</body>
</html>We're using a template as it makes it easier to show what you should do with assets that aren't the actual application.
You will need to install Flask itself, or at least set up virtual environments as recommended in the Flask Install guide.
Once you have activated the virtual environment, run:
python -m pip install -r requirements.txt
Which will load Flask and other required packages. One of those packages will be gunicorn which isn't a Flask dependency, but will be used when we deploy the app to Fly.
Flask apps are run with the flask run command, but before you do that, you need to set an environment variable FLASK_APP to say which app you want to run.
FLASK_APP=hellofly flask run * Serving Flask app "hellofly"
* Environment: production
WARNING: This is a development server. Do not use it in a production deployment.
Use a production WSGI server instead.
* Debug mode: off
* Running on http://127.0.0.1:5000/ (Press CTRL+C to quit)
This will run our hellofly app and you should be able to connect to it locally on localhost:5000.
Now, let's move on to deploying this app to Fly.
We are ready to start working with Fly and that means we need flyctl, our CLI app for managing apps on Fly. If you've already installed it, carry on. If not, hop over to our installation guide. Once that is installed you'll want to login to Fly.
Each Fly application needs a fly.toml file to tell the system how we'd like to deploy it. That file can be automatically generated with the command flyctl launch command. We are going to use one of Fly's builtin deployment configurations for Python.
flyctl launchCreating app in /<path>/python-hellofly-flask
Scanning source code
Detected a Python app
Using the following build configuration:
Builder: paketobuildpacks/builder:base
Selected App Name:
? Select region: lhr (London, United Kingdom)
Created app hellofly-flask in organization personal
Wrote config file fly.toml
We have generated a simple Procfile for you. Modify it to fit your needs and run "fly deploy" to deploy your application.
You'll be asked for an application name first. We recommend that you go with the autogenerated names for apps to avoid namespace collisions. We're using hellofly-python here so you can easily spot it in configuration files.
Next you'll be prompted for an organization. Organizations allow sharing applications between Fly users. When you are asked to select an organization, there should be one with your account name; this is your personal organization. Select that.
Now flyctl launch will generate a sample Procfile and fly.toml, which together will define how fly deploys and launches the application.
Update the Procfile to look like this:
web: gunicorn hellofly:appThis says the web component of the application is served by gunicorn (which we mentioned earlier when talking about dependencies) and that it should run the hellofly Flask app.
The fly.toml file now contains a default configuration for deploying your app. In the process of creating that file, flyctl has also created a Fly-side application slot of the same name, hellofly-python. If we look at the fly.toml file we can see the name in there:
# fly.toml file generated for hellofly-python on 2021-11-30T17:37:33+02:00
app = "hellofly-python"
kill_signal = "SIGINT"
kill_timeout = 5
processes = []
[build]
builder = "paketobuildpacks/builder:base"
[env]
PORT = "8080"
[experimental]
allowed_public_ports = []
auto_rollback = true
[[services]]
http_checks = []
internal_port = 8080
processes = ["app"]
protocol = "tcp"
script_checks = []
[services.concurrency]
hard_limit = 25
soft_limit = 20
type = "connections"
[[services.ports]]
handlers = ["http"]
port = 80
[[services.ports]]
handlers = ["tls", "http"]
port = 443
[[services.tcp_checks]]
grace_period = "1s"
interval = "15s"
restart_limit = 0
timeout = "2s"The flyctl command will always refer to this file in the current directory if it exists, specifically for the app name/value at the start. That name will be used to identify the application to the Fly service. The rest of the file contains settings to be applied to the application when it deploys.
We'll have more details about these properties as we progress, but for now, it's enough to say that they mostly configure which ports the application will be visible on.
We are now ready to deploy our app to the Fly platform. At the command line, just run:
flyctl deployThis will lookup our fly.toml file, and get the app name hellofly-python from there. Then flyctl will start the process of deploying our application to the Fly platform. Flyctl will return you to the command line when it's done.
Now the application has been deployed, let's find out more about its deployment. The command flyctl status will give you all the essential details.
flyctl statusApp
Name = hellofly-python
Owner = demo
Version = 0
Status = running
Hostname = hellofly-python.fly.dev
Deployment Status
ID = 0cdc72fe-3db9-aa52-eb84-5c3552053b1e
Version = v0
Status = successful
Description = Deployment completed successfully
Instances = 1 desired, 1 placed, 1 healthy, 0 unhealthy
Instances
ID VERSION REGION DESIRED STATUS HEALTH CHECKS RESTARTS CREATED
0530d622 0 lhr run running 1 total, 1 passing 0 40s ago
As you can see, the application has been with a DNS hostname of hellofly-python.fly.dev, and an instance is running in London. Your deployment's name will, of course, be different.
The quickest way to connect to your deployed app is with the flyctl open command. This will open a browser on the HTTP version of the site. That will automatically be upgraded to an HTTPS secured connection (for the fly.dev domain).
to connect to it securely. Add /name to flyctl open and it'll be appended to the URL as the path and you'll get an extra greeting from the hellofly-python application.
If you want to know what IP addresses the app is using, try flyctl ips list:
fly ips listTYPE ADDRESS CREATED AT
v4 213.188.195.22 2m1s ago
v6 2a09:8280:1:502e:4ce8:6058:7f09:62a 1m58s ago
And you can always run flyctl as fly if you want to save a few keystrokes.
You have successfully built, deployed, and connected to your first Python application on Fly.