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.

283 comments

  • #126 Miguel Grinberg said 2019-05-06T21:16:24Z

    @Yuri: what is the stack trace when you interrupt the process with Ctrl-C?

  • #127 Chris said 2019-06-20T19:03:37Z

    Hello again Miguel! What do you mean when you mention child processes of gunicorn here "[...] also reaches the child processes of the top-level gunicorn process."? Can you give me an example of a child process please. Thanks.

  • #128 Miguel Grinberg said 2019-06-20T21:08:02Z

    @Chris: when you run gunicorn as indicated in this article you'll end up with 5 processes. The main gunicorn process will own 4 child processes, which are the workers that respond to requests.

  • #129 Flaskjacket said 2019-09-11T07:22:34Z

    Miguel -- I suggest explicitly telling readers unfamiliar with UNIX behavior that the filename of the NGINX conf snippet is 'microblog' with no extension and not to be confused with a directory location. I misinterpreted your instructions that what to call it was an omitted detail and saved it "/sites-enabled/microblog/nginx.conf." This prevented NGINX from running. I then renamed it 'microblog' upon looking at your github repository, and then I received "(error 21: Is a directory)" because of the /microblog/microblog confusion. Or was this an intentional feature designed to develop my technical sophistication? ;)

  • #130 Miguel Grinberg said 2019-09-11T13:55:24Z

    @Flaskjacket: every snippet of code in this tutorial includes a heading that shows the exact filename for the file the snippet belongs to, so that can be used for additional validation when the text of the article may seem ambiguous.

  • #131 Doug Leister said 2019-09-13T01:01:26Z

    Hi Miguel, Thanks for the wonderful tutorial. A year later, it is still getting plenty of use and is an invaluable learning tool. I've been following along and am working on the initial db migration for my db in mysql. To be clear, my project is a bit different from the microblog. One issue I came across in the alembic files was the dialect differences between sqlite and mysql (i.e. batch operations in sqlite, etc.) and need to manually adjust alembic files. Could you share best practices on managing this? It seems risky/messy to build/test the migration file on sqlite and then manually adjust for mysql. Best, Doug

  • #132 Miguel Grinberg said 2019-09-13T12:16:47Z

    @Doug: I don't recall having the batch option enabled being a problem for MySQL or Postgres. But in general, you can avoid a lot of problems if you use the same database server for development and production. You can still use sqlite for testing, but the tests will create the database by calling "db.create_all()" instead of going through alembic.

  • #133 pick said 2019-10-29T01:34:53Z

    Thanks for the tutorial! I got stuck while trying to run pip install -r requirements.txt and I got this error (venv) vagrant@ubuntu-xenial:~/Flask$ pip install -r requirements.txt Collecting alembic==1.2.1 (from -r requirements.txt (line 1)) Could not find a version that satisfies the requirement alembic==1.2.1 (from -r requirements.txt (line 1)) (from versions: ) No matching distribution found for alembic==1.2.1 (from -r requirements.txt (line 1 I thought that something was wrong with my repository but then tried installing it after cloning your repository but got the same error Do you know what could have caused this? Thanks

  • #134 Miguel Grinberg said 2019-10-29T01:55:57Z

    @pick: Maybe the python package repository was temporarily down when you attempted this, or else you were not connected to the Internet.

  • #135 apk14 said 2020-01-19T15:26:02Z

    Hey, thanks again for this wonderful tutorial. I implemented the free alternative using virtualbox and vagrant and followed the steps exactly as you mentioned but the "sudo service nginx reload" command failed with error "Job for nginx.service failed because the control process exited with error code. See "systemctl status nginx.service" and "journalctl -xe" for details." The output of nginx -t was "nginx: [warn] the "user" directive makes sense only if the master process runs with super-user privileges, ignored in /etc/nginx/nginx.conf:1 nginx: [crit] pread() "/etc/nginx/sites-enabled/microblog" failed (21: Is a directory) nginx: configuration file /etc/nginx/nginx.conf test failed " Then the above mentioned file got deleted while trying to resolve this issue. the reload still fails and now the output of nginx -t is "nginx: [emerg] open() "/etc/nginx/nginx.conf" failed (2: No such file or directory) nginx: configuration file /etc/nginx/nginx.conf test failed" What should I do now?

  • #136 Miguel Grinberg said 2020-01-19T18:36:02Z

    @apk14: the error from nginx appears to say that the file /etc/nginx/sites-enabled/microblog is not a file but is a directory. This is the config file for the app, it should be a file, as shown in this article.

  • #137 apk14 said 2020-01-20T03:25:34Z

    Oh, I thought the configuration file is to be created in /etc/sites-enabled/microblog/ as file.conf or something. Now is there any way to get back the deleted file, or will I have to set up the server again? Also, I tried the setup on heroku as you provided in the next chapter and wanted to know how do I setup the postgres database on heroku. What I found online was to first set it up in the local repository and then to use git push. Isn't there any other way? I mean the database exists and is currently empty and I don't know how fill it up with the tables the project contains.

  • #138 Miguel Grinberg said 2020-01-20T11:06:40Z

    @apk14: I don't understand what deleted file you are asking about. All you need to do is remove the microblog directory under sites-enabled, and then put a file with that name there with the contents shown in this article.

    The Heroku tutorial explains how to set up a Postgres database.

  • #139 apk14 said 2020-01-20T12:51:40Z

    I am asking about the nginx.conf file in etc/nginx directory that is I think already created when the server is set up. The error I pasted in my previous comment says that it is missing.

  • #140 apk14 said 2020-01-20T14:09:14Z

    Ok, I got that file back and now nginx gets started but the browser shows 502:Bad gateway error

  • #141 Miguel Grinberg said 2020-01-22T02:15:54Z

    @ apk14: If you corrupted your installation of nginx by deleting a file, I suggest you uninstall it and then re-install it.

  • #142 Lord Cheta said 2020-01-27T11:34:26Z

    Hi Miguel Grinberg great job on this tutorial. I've successfully deployed my application on digital ocean. But i get a 500 error when I try to do any database operation. I'm still using the sqlite3 db as it's fine for my use case. Flask shell works fine as I can query the db. I've been stuck on this for days now. Please help.

  • #143 Miguel Grinberg said 2020-01-27T15:16:30Z

    @Lord: any time you get a 500 error you need to look at the output of the Flask process, either on the terminal if you are running it directly, or in the log if you are running it as a service. That's the only way to find out what's the error about, unfortunately I have no way to know.

  • #144 Lord Cheta said 2020-01-28T14:53:09Z

    213.32.122.82 - - [28/Jan/2020:00:29:28 +0000] "GET / HTTP/1.1" 200 3633 "-" "Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2228.0 Sa$ 184.105.139.67 - - [28/Jan/2020:00:31:47 +0000] "GET / HTTP/1.1" 200 3633 "-" "-" 3.94.250.69 - - [28/Jan/2020:01:18:01 +0000] "GET / HTTP/1.1" 400 280 "-" "Cloud mapping experiment. Contact research@pdrlabs.net" 198.108.66.80 - - [28/Jan/2020:03:27:53 +0000] "GET / HTTP/1.1" 200 1500 "-" "Mozilla/5.0 zgrab/0.x" 83.97.20.35 - - [28/Jan/2020:03:33:51 +0000] "GET / HTTP/1.0" 200 3633 "-" "-" 169.197.108.42 - - [28/Jan/2020:06:54:08 +0000] "GET /Telerik.Web.UI.WebResource.axd?type=rau HTTP/1.1" 404 209 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWeb$ 128.14.133.58 - - [28/Jan/2020:09:28:09 +0000] "GET /remote/login HTTP/1.1" 404 209 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Geck$ 185.156.177.50 - - [28/Jan/2020:11:52:40 +0000] "\x03\x00\x00/*\xE0\x00\x00\x00\x00\x00Cookie: mstshash=Administr" 400 182 "-" "-" 197.211.61.102 - - [28/Jan/2020:14:34:40 +0000] "GET /admin HTTP/1.1" 200 1728 "https://ipointe.co/modules" "Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:72.0) Gecko/201$ 197.211.61.102 - - [28/Jan/2020:14:34:40 +0000] "GET /static/styles/main.css HTTP/1.1" 200 2478 "https://ipointe.co/admin" "Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:$ 197.211.61.102 - - [28/Jan/2020:14:34:43 +0000] "GET /admin HTTP/1.1" 200 1729 "https://ipointe.co/modules" "Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:72.0) Gecko/201$ 197.211.61.102 - - [28/Jan/2020:14:34:43 +0000] "GET /static/styles/main.css HTTP/1.1" 200 2478 "https://ipointe.co/admin" "Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:$ 197.211.61.102 - - [28/Jan/2020:14:34:44 +0000] "GET /static/assets/logo.png HTTP/1.1" 200 13996 "https://ipointe.co/admin" "Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv$ 197.211.61.102 - - [28/Jan/2020:14:34:46 +0000] "POST /admin HTTP/1.1" 500 290 "https://ipointe.co/admin" "Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:72.0) Gecko/20100$ 197.211.61.102 - - [28/Jan/2020:14:34:47 +0000] "GET /favicon.ico HTTP/1.1" 404 209 "-" "Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:72.0) Gecko/20100101 Firefox/72.0"

    Above is the most recent log. Notice for the admin post. That's where is supposed to take data from log in form, check against the db then log in the desired route. I don't know any actionable info I can get from it

  • #145 Miguel Grinberg said 2020-01-28T19:43:08Z

    @Lord: you are looking at your web server's log. I'm talking about the Flask log, that's where you will find stack traces for errors. Not sure how you have logging configured for your app, so I cannot tell you where this log is for your application.

  • #146 dman said 2020-01-29T19:38:29Z

    Hi Miguel, love your tutorial and was wondering if you could help me with a problem I've been having. I skipped the majority of the chapter only did a subset of "Installing the Application." I'm running a clean version of ubuntu 18.04 on virtualbox that wouldn't have anything done from past chapters. I cloned your git repository but didn't checkout to 17.0, created and activated the venv, downloaded the requirements.txt dependencies and then tried to run the app after that hoping it would work still with sqlite. The app runs and loads the initial login page, but I keep getting this error when trying to submit on login or register pages.

    127.0.0.1 - - [29/Jan/2020 14:16:56] "POST /auth/login?next=%2F HTTP/1.1" 500 - Traceback (most recent call last): File "/home/darren/microblog/venv/lib/python3.6/site-packages/flask/app.py", line 2309, in call return self.wsgi_app(environ, start_response) File "/home/darren/microblog/venv/lib/python3.6/site-packages/flask/app.py", line 2295, in wsgi_app response = self.handle_exception(e) File "/home/darren/microblog/venv/lib/python3.6/site-packages/flask/app.py", line 1741, in handle_exception reraise(exc_type, exc_value, tb) File "/home/darren/microblog/venv/lib/python3.6/site-packages/flask/_compat.py", line 35, in reraise raise value File "/home/darren/microblog/venv/lib/python3.6/site-packages/flask/app.py", line 2292, in wsgi_app response = self.full_dispatch_request() File "/home/darren/microblog/venv/lib/python3.6/site-packages/flask/app.py", line 1815, in full_dispatch_request rv = self.handle_user_exception(e) File "/home/darren/microblog/venv/lib/python3.6/site-packages/flask/app.py", line 1718, in handle_user_exception reraise(exc_type, exc_value, tb) File "/home/darren/microblog/venv/lib/python3.6/site-packages/flask/_compat.py", line 35, in reraise raise value File "/home/darren/microblog/venv/lib/python3.6/site-packages/flask/app.py", line 1813, in full_dispatch_request rv = self.dispatch_request() File "/home/darren/microblog/venv/lib/python3.6/site-packages/flask/app.py", line 1799, in dispatch_request return self.view_functionsrule.endpoint File "/home/darren/microblog/app/auth/routes.py", line 19, in login user = User.query.filter_by(username=form.username.data).first() File "/home/darren/microblog/venv/lib/python3.6/site-packages/sqlalchemy/orm/query.py", line 2755, in first ret = list(self[0:1]) File "/home/darren/microblog/venv/lib/python3.6/site-packages/sqlalchemy/orm/query.py", line 2547, in getitem return list(res) File "/home/darren/microblog/venv/lib/python3.6/site-packages/sqlalchemy/orm/query.py", line 2855, in iter return self._execute_and_instances(context) File "/home/darren/microblog/venv/lib/python3.6/site-packages/sqlalchemy/orm/query.py", line 2878, in _execute_and_instances result = conn.execute(querycontext.statement, self._params) File "/home/darren/microblog/venv/lib/python3.6/site-packages/sqlalchemy/engine/base.py", line 945, in execute return meth(self, multiparams, params) File "/home/darren/microblog/venv/lib/python3.6/site-packages/sqlalchemy/sql/elements.py", line 263, in _execute_on_connection return connection._execute_clauseelement(self, multiparams, params) File "/home/darren/microblog/venv/lib/python3.6/site-packages/sqlalchemy/engine/base.py", line 1053, in _execute_clauseelement compiled_sql, distilled_params File "/home/darren/microblog/venv/lib/python3.6/site-packages/sqlalchemy/engine/base.py", line 1189, in _execute_context context) File "/home/darren/microblog/venv/lib/python3.6/site-packages/sqlalchemy/engine/base.py", line 1402, in _handle_dbapi_exception exc_info File "/home/darren/microblog/venv/lib/python3.6/site-packages/sqlalchemy/util/compat.py", line 203, in raise_from_cause reraise(type(exception), exception, tb=exc_tb, cause=cause) File "/home/darren/microblog/venv/lib/python3.6/site-packages/sqlalchemy/util/compat.py", line 186, in reraise raise value.with_traceback(tb) File "/home/darren/microblog/venv/lib/python3.6/site-packages/sqlalchemy/engine/base.py", line 1182, in _execute_context context) File "/home/darren/microblog/venv/lib/python3.6/site-packages/sqlalchemy/engine/default.py", line 470, in do_execute cursor.execute(statement, parameters) sqlalchemy.exc.OperationalError: (sqlite3.OperationalError) no such table: user [SQL: 'SELECT user.id AS user_id, user.username AS user_username, user.email AS user_email, user.password_hash AS user_password_hash, user.about_me AS user_about_me, user.last_seen AS user_last_seen \nFROM user \nWHERE user.username = ?\n LIMIT ? OFFSET ?'] [parameters: ('dan', 1, 0)]

    I've tried checking out to v17, installing gunicorn and pymysql, creating the .env file without the database_url, setting the FLASK_APP environment variable (flask help does show translate) but none of these have fixed the problem. Any chance you know what the issue is? Shouldn't things still work with what I did? What am I missing here?

  • #147 Miguel Grinberg said 2020-01-30T10:04:12Z

    @dman: you haven't created your database. Run "flask db upgrade" to do that.

  • #148 dman said 2020-01-30T16:23:23Z

    Thanks Miguel! That was it!

    Would this need to be done before each deployment and if I followed the above instructions to use MySQL instead of sqlite, would it still need to be done?

    I'm also curious about your preferred method of working with MySQL databases during development. I'm thinking of something along the lines of PhpMyAdmin, is there an application you use or that most web developers use? I know you mention WWW SQL DESIGNER, which seems a useful tool for planning database layouts, but do you use anything else for easy viewing and editing of the database.

    Thanks so much for your help. You are the man!

  • #149 Miguel Grinberg said 2020-01-31T23:17:17Z

    @dman: the upgrade command is issued to bring the database to the most current version. You should issue it on every installation every time you deploy an upgrade, or in development as needed.

    I don't normally need to modify a database directly, I do all the schema changes through database migrations. For quick queries I usually run the mysql cli, but phpMyAdmin and/or SQL designer are good tools, use them if you like them.

  • #150 Kim G said 2020-02-12T21:00:45Z

    Hola Miguel, I am having a couple issues within this deployment chapter. I am attempting with the Vagrant / VirtualBox configuration.

    When I try to install git clone into vagrant@ubuntu-xenial:/homeI get permission denied although I can clone to the root user in Vagrant, and the error message for changing permissions: chmod 777 /home chmod: changing permissions of '/home': Operation not permitted

    Cannot load the server (from same root path) using gunicorn commands with or without the 127.0.0.1 prefix, using different browsers or port numbers, nor with flask run. In the terminal it boots up without errors, All browsers read unable to connect.

    Gracias, Kim

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