pytwask¶

Source code and development docker image:

Production docker image:

A toy-twitter-clone frontend using Python and Flask.

To run this Flask application locally in the production mode,

$ pip install pytwask
$ export FLASK_APP=autopytwask
$ export PYTWASK_ENV=prod
$ flask run

For how to run the application in the development mode, please refer to Section 5.

For how to deploy the application via docker, please refer to Section 4.2.

Table of Contents¶

1. Features
2. Backend database
3. MTV architecture
4. Deployment
5. Development
6. PEP8
7. README.rst

1. Features¶

This module implements the frontend for a simplified Twitter clone based on Flask.

It supports the following features:

Register new users
Log in/out
Change user password
Get user profile
Post tweets
Follower/Following
General timeline for anonymous user
User timeline
Get tweets posted by one user

TODOs:

Search users
Delete a user
Recover user password
#hashtags
@mentions
Retweets
Replies
Conversations
Edit/Delete tweets
And more

2. Backend database¶

Although currently we only have Redis as the only type of backend database, we can easily switch to another type of backend database as long as the backend module conforms to the same interface as the Redis backend module pytwis.

By default this Flask application will connect to the Redis database via a TCP/IP connection. To connect to a local Redis database via a UNIX domain socket, define the environment variable REDIS_DB_SOCKET as the socket file (e.g., /tmp/redis.sock) before running the application.

$ export REDIS_DB_SOCKET="/tmp/redis.sock"
$ export FLASK_APP=autopytwask
$ flash run

Note that the UNIX domain socket is by default disabled in Redis and you need to manually enable it in the Redis configuration file (usually /etc/redis/redis.conf) before use it.

3. MTV architecture¶

This Flask application follows the typical Flask Model-Template-View pattern. Its directory layout follows the ones given at

Specifically,

.
├── autopytwask.py    # The Flask script which creates this Flask application
└── pytwask
    ├── auth          # The authentication blueprint
    ├── config.py     # The Flask application configuration file
    ├── __init__.py
    ├── main          # The main blueprint
    ├── models.py     # The data Model
    ├── static        # The HTML resources (css, images, javascript)
    ├── templates     # The HTML Templates
    └── tweets        # The tweets blueprint

4. Deployment¶

4.1. Deploy the Flask application in the cloud.¶

Take the Amazon Web Service (AWS) as an example. Assume that we have created an EC2 instance with Ubuntu 16.04LTS, exposed its HTTP port 80, and SSH’ed into it.

4.1.1. Install Python 3.6, pip, pip3, virtualenvwrapper.¶

(1) Install Python 3.6 from source.

# Download the latest source release of Python 3.6.
$ wget https://www.python.org/ftp/python/3.6.5/Python-3.6.5.tgz

# Unpack the downloaded archive.
$ tar -xvf Python-3.6.5.tgz

# Build and install.
$ cd Python-3.6.5
$ ./configure
$ make
$ make install

# Verify the installation.
$ python3.6 -V
Python 3.6.5

(2) Install pip and pip3.

$ sudo apt install python-pip python3-pip

(3) Install virtualenvwrapper.

$ sudo pip3 install virtualenvwrapper

4.1.2. Create a separate user which will run the Flask application.¶

We should never run the Flask application as root. If we do that, once the Flask application is compromised somehow, the attacker will gain access to the entire system.

$ sudo adduser flask-apps

4.1.3. Create the virtual environment for running the Flask application.¶

(1) Set up `virtualenvwrapper` for the user `flask-apps`.

$ sudo su - flask-apps
$ vi ~/.bashrc

Add the following lines in .bashrc.

export WORKON_HOME=$HOME/.virtualenvs
export VIRTUALENVWRAPPER_VIRTUALENV_ARGS='--no-site-packages'
source /usr/local/bin/virtualenvwrapper.sh

(2) Reload `.bashrc` and create a virtual environment for running the Flask application.

$ cd
$ source .bashrc
$ mkvirtualenv -p /usr/bin/python3.6 pytwask

Note that the binary location of python3.6 may vary on different machines but it can be easily found by which python3.6.

4.1.4. Install the Python WSGI HTTP server `Gunicorn` and the Flask application `pytwask` in the above virtual environment `flask-apps`.¶

# After mkvirtualenv is done, the virtual environment flask-apps should be automatically activated.
# But if not, we can manually activate it.
$ workon pytwask

(pytwask) $ pip install gunicorn pytwask

4.1.5. Install and configure nginx.¶

(1) Install nginx.

# Exit the user flask-apps
$ exit

$ sudo apt install nginx

(2) Configure nginx to proxy requests.

* Optimize the nginx parameter `default_type` for the Flask application.

According to http://www.patricksoftwareblog.com/how-to-configure-nginx-for-a-flask-web-application/, for a Flask application that is generating dynamic HTML files, the parameter `default_type` should be changed to: `default_type text/html;`.

$ sudo vi /etc/nginx/nginx.conf

http {
    ......

    include /etc/nginx/mime.types;
    default_type text/html; # was application/octet-stream

    ......
}

* Create a configuration file for pytwask.

$ sudo vi /etc/nginx/sites-available/pytwask

Note that we will pass requests to the socket we defined using the proxy_pass directive.

server {
    listen      80;
    server_name [SERVER_DNS_NAME OR SERVER_IP];

    location / {
        include proxy_params;
        proxy_pass http://unix:/tmp/pytwask.sock;
    }
}

* Enable the above server configuration by linking the file to the `sites-enabled` directory.

$ sudo ln -s /etc/nginx/sites-available/pytwask /etc/nginx/sites-enabled

* Test the configuration file for syntax error.

$ sudo nginx -t

* Restart nginx to load the new configuration.

$ sudo service nginx restart

4.1.6. Start a Gunicorn process to serve the Flask application.¶

$ sudo su - flask-apps

# Here we use the UNIX domain socket to connect to the Redis database.
# If you want to use the TCP/IP connection, then don't define the environment variable REDIS_DB_SOCKET.
$ export PYTWASK_ENV=prod
$ export REDIS_DB_SOCKET="/tmp/redis.sock"
$ export REDIS_DB_PASSWORD="[PASSWORD]"

$ workon pytwask
(pytwask) $ gunicorn -b unix:/tmp/pytwask.sock -m 007 -w 4 autopytwask:app &

Note that the ampersand “&” will set the Gunicorn process off running in the background.

4.1.7. (Optional) Create a systemd unit file and enable the Gunicorn process as a service.¶

(1) Create a unit file ending in `.service` within the directory `/etc/systemd/system`.

$ sudo vi /etc/systemd/system/pytwask.service

(2) Add the section `[Unit]` to specify metadata and dependencies.

[Unit]
Description=Gunicorn instance to serve pytwask
After=network.target

(3) Add the section `[Service]` to specify:

* the user `flask-apps` and group `www-data` that we want the process to run under;
* the working directory and set various environment variables;
* the command to start the service.

Note that we give the group ownership to group `www-data` so that nginx can communicate easily with the Gunicorn process.

[Unit]
Description=Gunicorn instance to serve pytwask
After=network.target

[Service]
User=flask-apps
Group=www-data
WorkingDirectory=/home/flask-apps/.virtualenvs
Environment="PATH=/home/flask-apps/.virtualenvs/pytwask/bin"
Environment="PYTWASK_ENV=prod"
Environment="REDIS_DB_SOCKET=/tmp/redis.sock"
Environment="REDIS_DB_PASSWORD=[PASSWORD]"
ExecStart=/home/flask-apps/.virtualenvs/pytwask/bin/gunicorn -b unix:/tmp/pytwask.sock -m 007 -w 4 autopytwask:app

(4) Add the section `[Install]` to tell systemd what to link this service to if we enable it to start at boot.

[Unit]
Description=Gunicorn instance to serve pytwask
After=network.target

[Service]
User=flask-apps
Group=www-data
WorkingDirectory=/home/flask-apps/.virtualenvs
Environment="PATH=/home/flask-apps/.virtualenvs/pytwask/bin"
Environment="PYTWASK_ENV=prod"
Environment="REDIS_DB_SOCKET=/tmp/redis.sock"
Environment="REDIS_DB_PASSWORD=[PASSWORD]"
ExecStart=/home/flask-apps/.virtualenvs/pytwask/bin/gunicorn -b unix:/tmp/pytwask.sock -m 007 -w 4 autopytwask:app

[Install]
WantedBy=multi-user.target

(5) Start the Gunicorn service and enable it to start at boot.

$ sudo systemctl start pytwask
$ sudo systemctl enable pytwask

4.2. Deploy the Flask application via docker.¶

Via docker, this flask application can be deployed not only on Linux but also on Windows, but note that when it is deployed on Docker for Windows, we need to switch to Linux containers.

4.2.1 Install docker and docker-compose.¶

For docker, see https://docs.docker.com/install/.

For docker-compose, see https://docs.docker.com/compose/install/#install-compose.

4.2.2 Download the docker-compose yml file.¶

$ wget https://raw.githubusercontent.com/renweizhukov/docker-pytwask/master/docker-compose.yml

4.2.3 Build services.¶

$ docker-compose build

4.2.4 Create and start containers.¶

$ docker-compose up -d

To stop and remove containers, networks, images, and volumes,

$ docker-compose down -v

4.3. Troubleshooting¶

4.3.1. Errors while reloading .bashrc for virtualenvwrapper.¶

/usr/bin/python3: Error while finding spec for 'virtualenvwrapper.hook_loader' (<class 'ImportError'>: No module named 'virtualenvwrapper')

To fix this, install python3-pip and then install virtualenvwrapper from pip3.

$ sudo apt install python3-pip
$ sudo pip3 install virtualwrapperenv

4.3.2. Errors while installing nginx.¶

To fix this, stop apache2 before installing nginx.

$ sudo service apache2 stop

As a further step, we may disable apache2 from startup or even remove apache2.

# To disable apache2
$ sudo update-rc.d apache2 disable

# To remove apache2
$ sudo update-rc.d -f apache2 remove

5. Development¶

By default, this Flask application will run in the development mode where the Flask DebugToolbar is enabled.

$ git clone https://github.com/renweizhukov/pytwask.git
$ cd pytwask
$ pip install -e .
$ export FLASK_APP=autopytwask
$ flask run

To launch the application in the development mode via docker, first install docker and docker-compose by following steps given in Section 4.2, and then build services, create and start containers.

$ git clone https://github.com/renweizhukov/pytwask.git

# Build services.
$ docker-compose -f docker-compose_dev.yml build

# Create and start containers in the detach mode.
$ docker-compose -f docker-compose_dev.yml up -d