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class: middle, center name: intro

  ___________________        
< Cowsay as a Service >      
  -------------------        
         \   ^__^            
           \  (oo)\________    
              (__)\        )\/\
                 ||----w |  
               ||     ||

Andreas Löf

Outline

  1. Introduction to web services
  2. Building a basic web service
  3. Dockerising it
  4. Deploying using Heroku
  5. A Slack Application written in Flask

What's a Web service?

  • A service offered by an electronic device to another electronic device, using HTTP
  • Supplies an API (SOAP, REST)
  • Fundamental building blocks in a service based architecture

REST (REpresentational State Transfer)

  • Builds on top of HTTP
  • Stateless operations
  • URL driven
    • Uses HTTP Keywords (POST, GET, PUT, DELETE)
    • CRUD
    • Status Codes (2xx, 3xx 4xx, 5xx)
  • Content negotiation
    • JSON
    • XML

???

2xx - Success 200 - Ok 201 - Created 202 - Accepted

3xx - Redirects

4xx - User error 400 - Bad Request 401 - Unauthorized 404 - Not found 405 - Method not allowed 409 - Conflict

5xx - Server Error

HTTP Request

GET /say/hello HTTP/1.1
Host: cowsay.io
User-Agent: Mozilla/5.0 (X11; Fedora; Linux x86_64; rv:60.0) Gecko/20100101 Firefox/60.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
Connection: keep-alive
Upgrade-Insecure-Requests: 1
DNT: 1
Cache-Control: max-age=0

HTTP Response

HTTP/1.1 200 OK
Connection: keep-alive
Server: gunicorn/19.8.1
Date: Sat, 09 Jun 2018 00:38:54 GMT
Content-Type: text/html; charset=utf-8
Content-Length: 1140
Via: 1.1 vegur

<!DOCTYPE html>
<html>
snip!
</html>

Building the Simplest Web Service in Flask

  • Flask
    • Lightweight
    • Web applications or services
    • Jinja2 templates
    • Lots of examples
    • Python 2 and 3
  • pip3 install Flask

Hello world:

from flask import Flask
app = Flask(__name__)


@app.route('/')
def hello_world():
   return 'Hello, World!'


if __name__ == '__main__':
   app.run()

Adding Content Negotiation

pip3 install flask-accept

from flask import Flask, jsonify
from flask_accept import accept
app = Flask(__name__)

@app.route('/')
@accept('text/html')
def hello_world():
    return 'Hello World!'

@hello_world.support('application/json')
def hello_world_json():
    return jsonify(result="Hello World!")

if __name__ == '__main__':
    app.run()

class: center, middle

Cowsay Codebase

https:/aginor/cowsay-as-a-service

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Content Negotiation Demo

Production Environments

  • Flask's built in server is not production grade
  • Make sure the Flask debugger is disabled
  • Manage credentials and secret keys securely
  • Serve static content from a proper webserver
    • No need to waste extra CPU-cycles in Flask
    • Apache or nginx will do it much more efficiently
  • WSGI interfaces
    • Gunicorn
    • uwsgi
    • mod_wsgi (Apache)
  • Deployment options
    • Virtual environments
    • Docker containers

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Never Commit a Key or Password

#Docker

  • Containerises applications
    • Not a VM!
  • Allows for shipping of application with dependencies
  • Separate the application from the system and vice-versa
  • Relies on kernel namespaces and control groups for security
# For debugging, gives 1 GB image
FROM python:3.6 
# For smaller images, ~ 90MB
#FROM python:3.6-alpine 

COPY requirements.txt /
RUN pip3 install --no-cache-dir -r /requirements.txt

COPY cowsay /cowsay
WORKDIR /
EXPOSE 8000

CMD gunicorn cowsay.app:app --bind=0.0.0.0 --workers=1 --log-file -

cowsay.io setup

  • Heroku for web hosting
    • Free plan
  • Cloudflare for DNS hosting
    • Could use caching but haven't enabled it
    • Supports rootless domains
    • Free plan

Deploying on Heroku

  • Platform as a Service (PaaS)

    • One of the first if not the first
    • Runs on top of AWS (ie, more expensive than plain AWS)

  • Comes with cli-tool for managing the application

  • Deploy by pushing to a git remote

git push heroku master

class: center, middle

Slack Application Consuming cowsay.io

https:/aginor/cowbot

Further Reading: