2018-03-27T21:30:02Z

The Flask Mega-Tutorial Part XVII: Deployment on Linux

This is the seventeenth installment of the Flask Mega-Tutorial series, in which I'm going to deploy Microblog to a Linux server.

For your reference, below is a list of the articles in this series.

In this chapter I'm reaching a milestone in the life of my Microblog application, as I'm going to discuss ways in which the application can be deployed on a production server so that it is accessible to real users.

The topic of deployment is extensive, and for that reason it is impossible to cover all the possible options here. This chapter is dedicated to explore traditional hosting options, and as subjects I'm going to use a dedicated Linux server running Ubuntu, and also the widely popular Raspberry Pi mini-computer. I will cover other options such as cloud and container deployments in later chapters.

The GitHub links for this chapter are: Browse, Zip, Diff.

Traditional Hosting

When I refer to "traditional hosting", what I mean is that the application is installed manually or through a scripted installer on a stock server machine. The process involves installing the application, its dependencies and a production scale web server and configure the system so that it is secure.

The first question you need to ask when you are about to deploy your own project is where to find a server. These days there are many economic hosting services. For example, for $5 per month, Digital Ocean, Linode, or Amazon Lightsail will rent you a virtualized Linux server in which to run your deployment experiments (Linode and Digital Ocean provision their entry level servers with 1GB of RAM, while Amazon provides only 512MB). If you prefer to practice deployments without spending any money, then Vagrant and VirtualBox are two tools that combined allow you to create a virtual server similar to the paid ones on your own computer.

As far as operating system choices, from a technical point of view, this application can be deployed on any of the major operating systems, a list which includes a large variety of open-source Linux and BSD distributions, and the commercial OS X and Microsoft Windows (OS X is a hybrid open-source/commercial option as it is based on Darwin, an open-source BSD derivative).

Since OS X and Windows are desktop operating systems that are not optimized to work as servers, I'm going to discard those as candidates. The choice between a Linux or a BSD operating system is largely based on preference, so I'm going to pick the most popular of the two, which is Linux. As far as Linux distributions, once again I'm going to choose by popularity and go with Ubuntu.

Creating an Ubuntu Server

If you are interested in doing this deployment along with me, you obviously need a server to work on. I'm going to recommend two options for you to acquire a server, one paid and one free. If you are willing to spend a little bit of money, you can get an account at Digital Ocean, Linode or Amazon Lightsail and create a Ubuntu 20.04 virtual server. You should use the smallest server option, which at the time I'm writing this, costs $5 per month for all three providers. The cost is prorated to the number of hours that you have the server up, so if you create the server, play with it for a few hours and then delete it, you would be paying just cents.

The free alternative is based on a virtual machine that you can run on your own computer. To use this option, install Vagrant and VirtualBox on your machine, and then create a file named Vagrantfile to describe the specs of your VM with the following contents:

Vagrantfile: Vagrant configuration.

Vagrant.configure("2") do |config|
  config.vm.box = "ubuntu/focal64"
  config.vm.network "private_network", ip: "192.168.33.10"
  config.vm.provider "virtualbox" do |vb|
    vb.memory = "2048"
  end
end

This file configures a Ubuntu 20.04 server with 2GB of RAM, which you will be able to access from the host computer at IP address 192.168.33.10. To create the server, run the following command:

$ vagrant up

Consult the Vagrant command-line documentation to learn about other options to manage your virtual server.

Using a SSH Client

Your server is headless, so you are not going to have a desktop on it like you have on your own computer. You are going to connect to your server through a SSH client and work on it through the command-line. If you are using Linux or Mac OS X, you likely have OpenSSH already installed. If you are using Microsoft Windows, Cygwin, Git, and the Windows Subsystem for Linux provide OpenSSH, so you can install any of these options.

If you are using a virtual server from a third-party provider, when you created the server you were given an IP address for it. You can open a terminal session with your brand new server with the following command:

$ ssh root@<server-ip-address>

You will be prompted to enter a password. Depending on the service, the password may have been automatically generated and shown to you after you created the server, or you may have given the option to choose your own password.

If you are using a Vagrant VM, you can open a terminal session using the command:

$ vagrant ssh

If you are using Windows and have a Vagrant VM, note that you will need to run the above command from a shell that can invoke the ssh command from OpenSSH.

Password-less Logins

If you are using a Vagrant VM, you can skip this section, since your VM is properly configured to use a non-root account named ubuntu, without password automatically by Vagrant.

If you are using a virtual server, it is recommended that you create a regular user account to do your deployment work, and configure this account to log you in without using a password, which at first may seem like a bad idea, but you'll see that it is not only more convenient but also more secure.

I'm going to create a user account named ubuntu (you can use a different name if you prefer). To create this user account, log in to your server's root account using the ssh instructions from the previous section, and then type the following commands to create the user, give it sudo powers, and finally switch to it:

$ adduser --gecos "" ubuntu
$ usermod -aG sudo ubuntu
$ su ubuntu

Now I'm going to configure this new ubuntu account to use public key authentication so that you can log in without having to type a password.

Leave the terminal session you have open on your server for a moment, and start a second terminal on your local machine. If you are using Windows, this needs to be the terminal from where you have access to the ssh command, so it will probably be a bash or similar prompt and not a native Windows terminal. In that terminal session, check the contents of the ~/.ssh directory:

$ ls ~/.ssh
id_rsa  id_rsa.pub

If the directory listing shows files named id_rsa and id_rsa.pub like above, then you already have a key. If you don't have these two files, or if you don't have the ~/.ssh directory at all, then you need to create your SSH keypair by running the following command, also part of the OpenSSH toolset:

$ ssh-keygen

This application will prompt you to enter a few things, for which I recommend you accept the defaults by pressing Enter on all the prompts. If you know what you are doing and want to do otherwise, you certainly can.

After this command runs, you should have the two files listed above. The file id_rsa.pub is your public key, which is a file that you will provide to third parties as a way to identify you. The id_rsa file is your private key, which should not be shared with anyone.

You now need to configure your public key as an authorized host in your server. On the terminal that you opened on your own computer, print your public key to the screen:

$ cat ~/.ssh/id_rsa.pub
ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQCjw....F8Xv4f/0+7WT miguel@miguelspc

This is going to be a very long sequence of characters, possibly spanning multiple lines. You need to copy this data to the clipboard, and then switch back to the terminal on your remote server, where you will issue these commands to store the public key:

$ echo <paste-your-key-here> >> ~/.ssh/authorized_keys
$ chmod 600 ~/.ssh/authorized_keys

The password-less login should now be working. The idea is that ssh on your machine will identify itself to the server by performing a cryptographic operation that requires the private key. The server then verifies that the operation is valid using your public key.

You can now log out of your ubuntu session, and then from your root session, and then try to login directly to the ubuntu account with:

$ ssh ubuntu@<server-ip-address>

This time you should not have to enter a password!

Securing Your Server

To minimize the risk of your server being compromised, there are a few steps that you can take, directed at closing a number of potential doors through which an attacker may gain access.

The first change I'm going to make is to disable root logins via SSH. You now have password-less access into the ubuntu account, and you can run administrator commands from this account via sudo, so there is really no need to expose the root account. To disable root logins, you need to edit the /etc/ssh/sshd_config file on your server. You probably have the vi and nano text editors installed in your server that you can use to edit files (if you are not familiar with either one, try nano first). You will need to prefix your editor with sudo, because the SSH configuration is not accessible to regular users (i.e. sudo vi /etc/ssh/sshd_config). You need to change a single line in this file:

/etc/ssh/sshd_config: Disable root logins.

PermitRootLogin no

Note that to make this change you need to locate the line that starts with PermitRootLogin and change the value, whatever that might be in your server, to no.

The next change is in the same file. Now I'm going to disable password logins for all accounts. You have a password-less login set up, so there is no need to allow passwords at all. If you feel nervous about disabling passwords altogether you can skip this change, but for a production server it is a really good idea, since attackers are constantly trying random account names and passwords on all servers hoping to get lucky. To disable password logins, change the following line in /etc/ssh/sshd_config:

/etc/ssh/sshd_config: Disable password logins.

PasswordAuthentication no

After you are done editing the SSH configuration, the service needs to be restarted for the changes to take effect:

$ sudo service ssh restart

The third change I'm going to make is to install a firewall. This is a software that blocks accesses to the server on any ports that are not explicitly enabled:

$ sudo apt-get install -y ufw
$ sudo ufw allow ssh
$ sudo ufw allow http
$ sudo ufw allow 443/tcp
$ sudo ufw --force enable
$ sudo ufw status

These commands install ufw, the Uncomplicated Firewall, and configure it to only allow external traffic on port 22 (ssh), 80 (http) and 443 (https). Any other ports will not be allowed.

Installing Base Dependencies

If you followed my advice and provisioned your server with the Ubuntu 20.04 release, then you have a system that comes with full support for Python 3.8, so this is the release that I'm going to use for the deployment.

The base Python interpreter is probably pre-installed on your server, but there are some extra packages that are likely not, and there are also a few other packages outside of Python that are going to be useful in creating a robust, production-ready deployment. For a database server, I'm going to switch from SQLite to MySQL. The postfix package is a mail transfer agent, that I will use to send out emails. The supervisor tool will monitor the Flask server process and automatically restart it if it ever crashes, or also if the server is rebooted. The nginx server is going to accept all request that come from the outside world, and forward them to the application. Finally, I'm going to use git as my tool of choice to download the application directly from its git repository.

$ sudo apt-get -y update
$ sudo apt-get -y install python3 python3-venv python3-dev
$ sudo apt-get -y install mysql-server postfix supervisor nginx git

These installations run mostly unattended, but at some point while you run the third install statement you will be prompted to choose a root password for the MySQL service, and you'll also be asked a couple of questions regarding the installation of the postfix package which you can accept with their default answers.

Note that for this deployment I'm choosing not to install Elasticsearch. This service requires a large amount of RAM, so it is only viable if you have a large server with more than 2GB of RAM. To avoid problems with servers running out of memory I will leave the search functionality out. If you have a big enough server, you can download the official .deb package from the Elasticsearch site and follow their installation instructions to add it to your server. Note that the Elasticsearch package available in the Ubuntu package repository might be too old so it may not work, so it is better to install it from the official source.

I should also note that the default installation of postfix is likely insufficient for sending email in a production environment. To avoid spam and malicious emails, many servers require the sender server to identify itself through security extensions, which means at the very least you have to have a domain name associated with your server. If you want to learn how to fully configure an email server so that it passes standard security tests, see the following Digital Ocean guides:

Installing the Application

Now I'm going to use git to download the Microblog source code from my GitHub repository. I recommend that you read git for beginners if you are not familiar with git source control.

To download the application to the server, make sure you are in the ubuntu user's home directory and then run:

$ git clone https://github.com/miguelgrinberg/microblog
$ cd microblog
$ git checkout v0.17

This installs the code on your server, and syncs it to this chapter. If you are keeping your version of this tutorial's code on your own git repository, you can change the repository URL to yours, and in that case you can skip the git checkout command.

Now I need to create a virtual environment and populate it with all the package dependencies, which I conveniently saved to the requirements.txt file in Chapter 15:

$ python3 -m venv venv
$ source venv/bin/activate
(venv) $ pip install -r requirements.txt

In addition to the common requirements in requirements.txt, I'm going to use three packages that are specific to this production deployment, so they are not included in the common requirements file. The gunicorn package is a production web server for Python applications. The pymysql package contains the MySQL driver that enables SQLAlchemy to work with MySQL databases. The cryptography package is used by pymsql to authenticate against the MySQL database server.

(venv) $ pip install gunicorn pymysql cryptography

I need to create a .env file, with all the needed environment variables:

/home/ubuntu/microblog/.env: Environment configuration.

SECRET_KEY=52cb883e323b48d78a0a36e8e951ba4a
MAIL_SERVER=localhost
MAIL_PORT=25
DATABASE_URL=mysql+pymysql://microblog:<db-password>@localhost:3306/microblog
MS_TRANSLATOR_KEY=<your-translator-key-here>

This .env file is mostly similar to the example I shown in Chapter 15, but I have used a random string for SECRET_KEY. To generate this random string I used the following command:

python3 -c "import uuid; print(uuid.uuid4().hex)"

For the DATABASE_URL variable I defined a MySQL URL. I will show you how to configure the database in the next section.

I need to set the FLASK_APP environment variable to the entry point of the application to enable the flask command to work, but this variable is needed before the .env file is parsed so it needs to be set manually. To avoid having to set it every time, I'm going to add it at the bottom of the ~/.profile file for the ubuntu account, so that it is set automatically every time I log in:

$ echo "export FLASK_APP=microblog.py" >> ~/.profile

If you log out and back in, now FLASK_APP will be set for you. You can confirm that it is set by running flask --help. If the help message shows the translate command added by the application, then you know the application was found.

And now that the flask command is functional, I can compile the language translations:

(venv) $ flask translate compile

Setting Up MySQL

The sqlite database that I've used during development is great for simple applications, but when deploying a full blown web server that can potentially need to handle multiple requests at a time, it is better to use a more robust database. For that reason I'm going to set up a MySQL database that I will call microblog.

To manage the database server I'm going to use the mysql command, which should be already installed on your server:

$ sudo mysql -u root
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 8
Server version: 8.0.25-0ubuntu0.20.04.1 (Ubuntu)

Copyright (c) 2000, 2021, Oracle and/or its affiliates.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql>

Note that you will need to use sudo to access the MySQL root user from the administrator account.

These are the commands that create a new database called microblog, and a user with the same name that has full access to it:

mysql> create database microblog character set utf8 collate utf8_bin;
mysql> create user 'microblog'@'localhost' identified by '<db-password>';
mysql> grant all privileges on microblog.* to 'microblog'@'localhost';
mysql> flush privileges;
mysql> quit;

You will need to replace <db-password> with a password of your choice. This is going to be the password for the microblog database user, so it is a good idea to not use the same password you selected for the root user. The password for the microblog user needs to match the password that you included in the DATABASE_URL variable in the .env file.

If your database configuration is correct, you should now be able to run the database migrations that create all the tables:

(venv) $ flask db upgrade

Make sure the above command completes without producing any errors before you continue.

Setting Up Gunicorn and Supervisor

When you run the server with flask run, you are using a web server that comes with Flask. This server is very useful during development, but it isn't a good choice to use for a production server because it wasn't built with performance and robustness in mind. Instead of the Flask development server, for this deployment I decided to use gunicorn, which is also a pure Python web server, but unlike Flask's, it is a robust production server that is used by a lot of people, while at the same time it is very easy to use.

To start Microblog under gunicorn you can use the following command:

(venv) $ gunicorn -b localhost:8000 -w 4 microblog:app

The -b option tells gunicorn where to listen for requests, which I set to the internal network interface at port 8000. It is usually a good idea to run Python web applications without external access, and then have a very fast web server that is optimized to serve static files accepting all requests from clients. This fast web server will serve static files directly, and forward any requests intended for the application to the internal server. I will show you how to set up nginx as the public facing server in the next section.

The -w option configures how many workers gunicorn will run. Having four workers allows the application to handle up to four clients concurrently, which for a web application is usually enough to handle a decent amount of clients, since not all of them are constantly requesting content. Depending on the amount of RAM your server has, you may need to adjust the number of workers so that you don't run out of memory.

The microblog:app argument tells gunicorn how to load the application instance. The name before the colon is the module that contains the application, and the name after the colon is the name of this application.

While gunicorn is very simple to set up, running the server from the command-line is actually not a good solution for a production server. What I want to do is have the server running in the background, and have it under constant monitoring, because if for any reason the server crashes and exits, I want to make sure a new server is automatically started to take its place. And I also want to make sure that if the machine is rebooted, the server runs automatically upon startup, without me having to log in and start things up myself. I'm going to use the supervisor package that I installed above to do this.

The supervisor utility uses configuration files that tell it what programs to monitor and how to restart them when necessary. Configuration files must be stored in /etc/supervisor/conf.d. Here is a configuration file for Microblog, which I'm going to call microblog.conf:

/etc/supervisor/conf.d/microblog.conf: Supervisor configuration.

[program:microblog]
command=/home/ubuntu/microblog/venv/bin/gunicorn -b localhost:8000 -w 4 microblog:app
directory=/home/ubuntu/microblog
user=ubuntu
autostart=true
autorestart=true
stopasgroup=true
killasgroup=true

The command, directory and user settings tell supervisor how to run the application. The autostart and autorestart set up automatic restarts due to the computer starting up, or crashes. The stopasgroup and killasgroup options ensure that when supervisor needs to stop the application to restart it, it also reaches the child processes of the top-level gunicorn process.

After you write this configuration file, you have to reload the supervisor service for it to be imported:

$ sudo supervisorctl reload

And just like that, the gunicorn web server should be up and running and monitored!

Setting Up Nginx

The microblog application server powered by gunicorn is now running privately port 8000. What I need to do now to expose the application to the outside world is to enable my public facing web server on ports 80 and 443, the two ports that I opened on the firewall to handle the web traffic of the application.

I want this to be a secure deployment, so I'm going to configure port 80 to forward all traffic to port 443, which is going to be encrypted. So I'm going to start by creating an SSL certificate. For now I'm going to create a self-signed SSL certificate, which is okay for testing everything but not good for a real deployment because web browsers will warn users that the certificate was not issued by a trusted certificate authority. The command to create the SSL certificate for microblog is:

$ mkdir certs
$ openssl req -new -newkey rsa:4096 -days 365 -nodes -x509 \
  -keyout certs/key.pem -out certs/cert.pem

The command is going to ask you for some information about your application and yourself. This is information that will be included in the SSL certificate, and that web browsers will show to users if they request to see it. The result of the command above is going to be two files called key.pem and cert.pem, which I placed in a certs sub-directory of the Microblog root directory.

To have a web site served by nginx, you need to write a configuration file for it. In most nginx installations this file needs to be in the /etc/nginx/sites-enabled directory. Nginx installs a test site in this location that I don't really need, so I'm going to start by removing it:

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

Below you can see the nginx configuration file for Microblog, which goes in /etc/nginx/sites-enabled/microblog:

/etc/nginx/sites-enabled/microblog: Nginx configuration.

server {
    # listen on port 80 (http)
    listen 80;
    server_name _;
    location / {
        # redirect any requests to the same URL but on https
        return 301 https://$host$request_uri;
    }
}
server {
    # listen on port 443 (https)
    listen 443 ssl;
    server_name _;

    # location of the self-signed SSL certificate
    ssl_certificate /home/ubuntu/microblog/certs/cert.pem;
    ssl_certificate_key /home/ubuntu/microblog/certs/key.pem;

    # write access and error logs to /var/log
    access_log /var/log/microblog_access.log;
    error_log /var/log/microblog_error.log;

    location / {
        # forward application requests to the gunicorn server
        proxy_pass http://localhost:8000;
        proxy_redirect off;
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    }

    location /static {
        # handle static files directly, without forwarding to the application
        alias /home/ubuntu/microblog/app/static;
        expires 30d;
    }
}

The nginx configuration is far from trivial, but I've added some comments so that at least you know what each section does. If you want to have information about a specific directive, consult the nginx official documentation.

After you add this file, you need to tell nginx to reload the configuration to activate it:

$ sudo service nginx reload

And now the application should be deployed. In your web browser, you can type the the IP address of your server (or 192.168.33.10 if you are using a Vagrant VM) and that will connect to the application. Because you are using a self-signed certificate, you will get a warning from the web browser, which you will have to dismiss.

After you complete a deployment with the above instructions for your own projects, I strongly suggest that you replace the self-signed certificate with a real one, so that the browser does not warn your users about your site. For this you will first need to purchase a domain name and configure it to point to your server's IP address. Once you have a domain, you can request a free Let's Encrypt SSL certificate. I have written a detailed article on my blog on how to Run your Flask application over HTTPS.

Deploying Application Updates

The last topic I want to discuss regarding the Linux based deployment is how to handle application upgrades. The application source code is installed in the server through git, so whenever you want to upgrade your application to the latest version, you can just run git pull to download the new commits that were made since the previous deployment.

But of course, downloading the new version of the code is not going to cause an upgrade. The server processes that are currently running will continue to run with the old code, which was already read and stored in memory. To trigger an upgrade you have to stop the current server and start a new one, to force all the code to be read again.

Doing an upgrade is in general more complicated than just restarting the server. You may need to apply database migrations, or compile new language translations, so in reality, the process to perform an upgrade involves a sequence of commands:

(venv) $ git pull                              # download the new version
(venv) $ sudo supervisorctl stop microblog     # stop the current server
(venv) $ flask db upgrade                      # upgrade the database
(venv) $ flask translate compile               # upgrade the translations
(venv) $ sudo supervisorctl start microblog    # start a new server

Raspberry Pi Hosting

The Raspberry Pi is a low-cost revolutionary little Linux computer that has very low power consumption, so it is the perfect device to host a home based web server that can be online 24/7 without tying up your desktop computer or laptop. There are several Linux distributions that run on the Raspberry Pi. My choice is Raspberry Pi OS, which is the official distribution from the Raspberry Pi Foundation.

To prepare the Raspberry Pi, I'm going to install a fresh Rasberry Pi OS release. I will be using the Lite version, because I do not need the desktop user interface. You can find the latest release of the Raspberry Pi OS on their operating systems page.

The Raspberry Pi OS image needs to be installed on an SD card, which you then plug into the Raspberry Pi so that it can boot with it. Instructions to copy the Raspberry Pi OS image to an SD card from Windows, Mac OS X and Linux are available on the Raspberry Pi site.

When you boot your Raspberry Pi for the first time, do it while connected to a keyboard and a monitor, so that you can do the set up. At the very least you should enable SSH, so that you can log in from your computer to perform the deployment tasks more comfortably.

Like Ubuntu, Raspberry Pi OS is a derivative of Debian, so the instructions above for Ubuntu Linux for the most part work just as well for the Raspberry Pi. However, you may decide to skip some of the steps if you are planning on running a small application on your home network, without external access. For example, you may not need the firewall, or the password-less logins. And you may want to use SQLite instead of MySQL in such a small computer. You may opt to not use nginx, and just have the gunicorn server listening directly for requests from clients. You will probably want just one or two gunicorn workers. The supervisor service is useful in ensuring the application is always up, so my recommendation is that you also use it on the Raspberry Pi.

292 comments

  • #51 Paul said 2018-06-21T10:59:49Z

    @miguel I really enjoyed working through your tutorial, which I did for the Kindle version, which rekindled (pun intended) my passion for coding. As an ex-coder in management, I forgot how much fun it was.

    Like @justin I had some issues with NGINX on Lightsail, but different... in my case the bog standard HTTP request on port 80 doesn’t seem to forward to 443, but I can access directly via HTTPS? And after posting a form I always get a 404 error, but going back correctly reloads the form and after navigating back to / the flash message is there and the update looks good.

    Any advice?

  • #52 Miguel Grinberg said 2018-06-21T18:53:28Z

    @Paul: what is the response when you send a request to HTTP (port 80)? If it is not a redirect, then what is it? The first server block in the nginx configuration controls port 80, and it is set to redirect, so you need to investigate what's happening instead of that. You can look in the browser's debugging, in the network tab.

    The form posting is also add and might be related to the other problem, since form posts are responded also with a redirect. For this it would also be useful to have more details on the requests and responses, so go to the network tab in your browser to see the details of that.

  • #53 Dave Reeves said 2018-06-22T15:58:57Z

    I get about a minute of downtime every time I push an update. I think supervisor is taking a while to start up back. Can you recommend a way of eliminating the downtime when deploying updates?

  • #54 Miguel Grinberg said 2018-06-22T18:14:07Z

    @Dave: I don't recall being that long for me. But in any case, zero-downtime deployments is hard. One way to achieve this is to have two complete deployments that you switch between by altering the nginx configuration, let's call them A and B. If nginx is configured to forward traffic to A, you deploy the upgrade to B, and only once the deployment is complete you modify nginx to now forward to B. Next time you need to do an upgrade you deploy to A and apply the same technique to switch.

  • #55 spmsh said 2018-06-25T12:56:44Z

    Hi Miguel,

    Thanks again for this. Once again you provided all the info needed with perfect explanation, and now I got my Flask + gunicorn + nginx on Ubuntu 18.4 almost from the first time.

    One question though, for my project, I'm also using your Flask-SocketIO module with eventlet.

    I'm now struggling about what would be best to run socketio. I've successfully run it on both gunicorn and with socketio.run(), together with nginx. However I read on other blogs/forums (some comments from yourself there as well) about the limitation of gunicorn because it doesn't handle load balancing well, and so we need to do that with several gunicorn, load balancing in nginx, and add a message queue... this seems a bit more complex thant using socketio.run().

    so the question, what is the most robust/recommended approach to run flask socketio ? Should I go with multiple gunicorn workers + nginx + redis ? or simply socketio.run + nginx ?

    Thanks a lot again !!

  • #56 Miguel Grinberg said 2018-06-27T15:00:16Z

    @spmsh: The easiest way is to run a single Flask process. Because you are using eventlet, that one process is going to handle hundreds or even thousands of concurrent clients. If that is insufficient, then you need to run several Flask processes (either with socketio.run() or by running multiple single-worker Gunicorns), and connect them all to the message queue.

  • #57 Florens said 2018-07-06T11:22:09Z

    I noticed you didn't install redis in this part. I did skip over some other chapters so maybe I missed something?

  • #58 Jason said 2018-07-06T12:57:28Z

    Hi Miguel, Thanks for your great tutorial. I met a problem when I tried to add uploading custom avatar. I saved the avatar in app/static/avatar directory and returned the url, everything is ok except that when the front-end try to get the avatar url, It is just return 403 forbidden. I have already checked my nginx configure file( alias /home/ubuntu/microblog/app/static; ) this line is ok. I hope I can get your help. Thanks again!

  • #59 Jason said 2018-07-06T14:02:48Z

    I've found the reson why 403, because the nginx can't read the static file, I just change the user directory to g+rx and add nginx user into the app user group. 😄

  • #60 Miguel Grinberg said 2018-07-06T14:23:46Z

    @Florens: Redis is introduced in a later chapter, up to this point it has not been used.

  • #61 spmsh said 2018-07-13T17:46:37Z

    Hi Miguel, thanks again for your reply and advice.

    I got another quick one, this time related to supervisor.

    I've setup everything as per ur guide and got it running well, however, I'm now facing problems with environment variables (it was hard-coded in config.py before).

    It seems supervisor creates/maintains its own environment, so all the vars from os.environ.get() always return none, even though it's added in the user profile running supervisorctl.

    Note that when running my program without supervisor, os.environ.get() returns the env vars correctly, problem only occurs when it's ran by supervisor, probably because supervisord is ran by root, not the current user where the env vars are defined.

    The workaround working for me is to add the vars directly into the supervisorctl conf file with one more line environment=xxx=xxx, xxx=xxx, ...

    Did you encounter the same problem ? Not sure if this workaround is best practices as there are a few passwords in this config file (email setup) Perhaps could be useful to add a note somewhere on this so other don't get stuck as much as I was.

    PS: for the ref, my config is Flask + your socketio with eventlet running on gunicorn (only 1 worker) by supervisor and nginx (reverse proxy)

    Thanks.

  • #62 Miguel Grinberg said 2018-07-13T18:13:19Z

    @spmsh: adding env vars in the supervisor configuration for your project is fine. I suppose you mean that config file, and not the main supervisor config file, correct? Another option that you have is to use a .env file in your project directory, which is automatically imported when your application starts. See Chapter 15 if you need a refresher on .env files.

  • #63 Warren Bain said 2018-07-26T11:39:55Z

    Thank you for such a great tutorial!

    I've put together some scripts and a Vagrantfile that will configure the vm and deploy the app without any intervention. You can see what I have done here: https://github.com/thoughtcroft/microblog

    Generally I create an ssh key pair per project. That way I can add the public key to the server and then update my ssh config file as per the following. This means I can simply issue an "ssh microblog" and all the magic just happens.

    $ cat ~/.ssh/config

    Host microblog HostName 127.0.0.1 User ubuntu Port 2222 IdentityFile ~/.ssh/microblog_rsa StrictHostKeyChecking no UserKnownHostsFile /dev/null LogLevel FATAL

    general settings

    PreferredAuthentications publickey IdentitiesOnly yes ServerAliveInterval 60

  • #64 Marek said 2018-08-01T10:57:32Z

    Hi Miguel,

    Thank you for this tutorial. The best I have ever read.

    One question. How do you assure the gunicorn runs within virtual environment ? There is no call to activate in the supervisor config file.

    Best regards, Marek

  • #65 Miguel Grinberg said 2018-08-01T22:40:52Z

    @Marek: the virtualenv activation is just a convenience option for yourself. You can run any executable installed in the virtualenv just by referencing it directly from the bin directory inside the virtualenv (or Scripts if you are on Windows). Note how I set the path to gunicorn to go into venv/bin/gunicorn.

  • #66 Samuel Diebolt said 2018-08-04T14:25:48Z

    Hello @Miguel,

    Thank you so much for this tutorial! I had never built a web application before – although I knew a bit of Python – and was able to build one to manage our student bar in my French engineering school thanks to you.

    This web app is now hosted on a Digital Ocean Droplet and I had no problem configuring it, adding a hostname, a SSL certificate, etc. However, I'd like to add a search function – since I can't use Elasticsearch, having only 1GB of RAM – to browse through clients using their username, first and last name, graduating class, etc. What would you recommend? Should I build this search function myself using sqlaclchemy?

    Best regards, Samuel

  • #67 Miguel Grinberg said 2018-08-04T21:31:10Z

    @Samuel: for simple searches, using the LIKE operator supported in relational databases might be enough. This operator is fully supported by SQLAlchemy.

  • #68 Zion Oyemade said 2018-08-23T13:04:43Z

    Hi Miguel, Great tutorial as always. I believe the Nginx configuration you outlined implies the Flask application will be the only instance running on the server. What changes if a different application is to be run from a different domain on the same server.

  • #69 Miguel Grinberg said 2018-08-25T10:43:00Z

    @Zion: For multiple servers, set the server_name to the proper domain in each configuration.

  • #70 Zheng L. said 2018-08-29T12:28:44Z

    Hi Miguel, Thanks a lot for your dedicated tutorial!

    Afters days of struggling I managed to deploy the little application on a VPS and direct my personal domain name to its IP address, but I then ran into the error of can't reaching the site.

    Say, when I'm reaching the /user/ I get a weird one: %20/user/%20HTTP/1.1-uri. I remember noticing a similar text in the configuration file of nginx like: return 301 https://$host$request_uri However I couldn't figure it our more on my own. Can you give me some hint or advice please?

  • #71 Miguel Grinberg said 2018-08-29T22:59:02Z

    @Zheng: the "%20" is a space character. Maybe you have extra spaces in the nginx config file?

  • #72 Kari said 2018-08-30T07:53:05Z

    Hi Miguel, I did everything exactly how you said in terms of getting vagrant, the virtualbox, and then the VagrantFile which I copied exactly how yours was. But the default user when I run 'vagrant ssh' (using a Mac) is vagrant and not ubuntu. I looked for an explanation and how to fix it, but I haven't been able to find anything conclusive.

    I tried going on with the tutorial as the vagrant user but I kept running into errors when I got up to the git part, and also with the requirements.txt - it said there was no such file. So i'm not sure if the default vagrant user was causing me problems or if I didn't clone my git repository to the right directory (however, it did say I was in the vagrant user's home directory when I checked).

  • #73 Miguel Grinberg said 2018-08-30T21:16:13Z

    @Kari: my guess is that you obtained your vagrant image from a different place than I did. I'm using the vagrant images from ubuntu, which come with a default user "ubuntu".

  • #74 James said 2018-09-03T12:51:01Z

    At one point, the instructions state: "The free alternative is based on a virtual machine that you can run on your own computer. To use this option, install Vagrant and VirtualBox on your machine, and then create a file named Vagrantfile to describe the specs of your VM with the following contents":

    I have installed Vagrant and VirtueBox successfully on my windows computer, but how do I go about creating the Vagrantfile? I tried the following "echo Vagrantfile" and it created an empty file. Exactly what should I do to create this file and should I populate with the information as the information in the file shown in the screenshot.?

  • #75 Miguel Grinberg said 2018-09-04T08:54:18Z

    @James: You can get the contents of the file from the GitHub repository. Here is a direct link to this file: https://github.com/miguelgrinberg/microblog/blob/master/Vagrantfile. You can copy/paste the contents of the file with your favorite text editor, for example.

Leave a Comment