Goal

Do a Hello World with a minimal web server.

Steps

Set up a VM in the cloud.
Install necessary tools.
Create an app.
Establish connection with WSGI protocol.
Set up an web server.
Tada!

1. Set up a VM in the cloud

Create a GCE f1-micro instance.

Required:
- Somewhere in the U.S. for using free tier.
- Allow HTTP traffic.
This time in GUI.
Using Ubuntu 18.04.

2. Install necessary tools

Open terminal.
Install the gcloud CLI.
- See: Using the Google Cloud SDK installer

$ curl https://sdk.cloud.google.com | bash
$ exec -l $SHELL
$ gcloud init

SSH into the VM.
- We don't have to remember this command, as it's shown in the web console.
- Go to the instances list page, click triangular icon right next to the SSH button, and then click view gcloud command.

$ gcloud compute --project "YOUR_PROJECT_ID" ssh --zone "us-east1-b" "YOUR_INSTANCE_NAME"

Update the package manager and installed packages.

$ sudo apt update
$ sudo apt upgrade

3. Create an app

Install python3.
- This enables the pip3 command.

$ sudo apt install python3 python3-dev python3-pip

Install virtualenv (may not be needed).

$ sudo apt install python3-vitualenv

Install Flask and uWSGI with pip3 (this time not apt).

$ sudo pip3 install flask

Create a Flask template file in the current directory.

~/hello.py

from flask import Flask

app = Flask(__name__)

@app.route("/")
def index():
    return "Hello World!"

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

Tell Flask about the app.

$ export FLASK_APP=hello.py

4. Establish connection with WSGI protocol.

Install uWSGI.

$ sudo pip3 install uwsgi

Create an uWSGI ini file.

~/uwsgi.ini

[uwsgi]

socket = /tmp/uwsgi.sock
chmod-socket = 666

chdir = %d
wsgi-file = /home/YOUR_USER_NAME/hello.py
module = hello:app
callable = app

master = 1
processes = 1

logto = /var/log/uwsgi/uwsgi.log

Create a service definition for systemd.
- Restart = always allowed?
- ExecStart should be noted absolute.

/etc/systemd/system/uwsgi.service

[Unit]
Description = uwsgi

[Service]
Restart = no
ExecStart = /usr/YOUR_USER_NAME/.local/bin/uwsgi --ini=/home/YOUR_USER_NAME/uwsgi.ini
ExecReload = /bin/kill -s HUP ${MAINPID}
KillSignal = QUIT

[Install]
WantedBy = multi-user.target

Enable (auto-restart) and start uwsgi manually.

$ sudo systemctl enable uwsgi
$ sudo systemctl start uwsgi

5. Set up an web server.

Install Nginx.

$ sudo apt install nginx

Note that configuration files are located under /etc/nginx.
- nginx.conf file is for global configuration and conf.d directory is for local one.
- Any .conf file put here is included into nginx.conf.
  - Look inside nginx.conf and see an include directive.

$ ls /etc/nginx | grep conf
conf.d
fastcgi.conf
nginx.conf

Remove the default conf file.

$ sudo rm /etc/nginx/sites-enabled/default

Create an Nginx conf file.
- uwsgi_pass directive specifies an unix socket.
- For details, look at this article.

/etc/nginx/conf.d/hello.conf

server {
  listen 80 default_server;
  server_name _;

  location / {
    include uwsgi_params;
    uwsgi_pass unix:///tmp/uwsgi.sock;
  }
}

Enable and start Nginx.

$ sudo systemctl enable nginx
$ sudo systemctl start nginx

6. Tada!

Open the fixed IP address in browser.

That's it!

If something's wrong...

First, do an research by taking a look at:
- on Nginx:
  - service status at $ systemctl status nginx
  - service declaration at /etc/systemd/system/uwsgi.service
  - conf files at /etc/nginx/nginx.conf or /etc/nginx/conf.d/hello.conf
- on uWSGI:
  - log at /var/log/uwsgi/uwsgi.log (if specified in logto directive in ~/uwsgi.ini)
  - service status at $ systemctl status uwsgi
  - conf file at ~/uwsgi.ini
- in general:
  - /var/log/syslog
  - $ history

References

in general:
- Ubuntu 16.04 で Flask アプリケーションを動かすまでにやることまとめ
- Flask + uWSGI + Nginx でハローワールドするまで @ さくらのVPS (CentOS 6.6)
  - for better understanding of each command.
- Deploying Python Flask using uWSGI and Nginx on Ubuntu 14.04
  - for errors like ImportError: No module named flask
uWSGI docs
- quickstart https://uwsgi-docs.readthedocs.io/en/latest/Configuration.html)
- details https://uwsgi-docs.readthedocs.io/en/latest/Options.html
Nginx configuration
- nginx初期構成
systemctl commands
- (https://qiita.com/sinsengumi/items/24d726ec6c761fc75cc9)
Flask basics
- http://flask.pocoo.org/docs/1.0/quickstart/
Python environments (e.g. difference among venv, virtualenv or pyenv)
- Pythonの環境構築を自分なりに整理してみる