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

  • #101 Miguel Grinberg said 2018-12-04T22:48:03Z

    @Rob: It's hard for me to know, since I do not know how your Postfix was installed and how your Flask app was configured. If you enable debug mode on the Flask app, then Flask-Mail will dump information to the terminal as it connects to the email server, maybe that will help you determine where the problem is.

  • #102 Felicia said 2018-12-09T10:19:33Z

    Just in case anybody else is struggling with it: In newer versions of MySQL it might be necessary to change the line create user 'microblog'@'localhost' identified by '<db-password>'; into create user 'microblog'@'localhost' identified with mysql_native_password by '<db-password>';

    to get it working (otherwise I always got an "Access Denied" error because MySQL changed the default authentication plugin settings in version 8.0). Maybe there is a better workaround, but at least I can use my database now.

  • #103 JG1212 said 2018-12-10T05:48:37Z

    Switching to MySQL utf8 breaks support for emojis and many other unicode characters that worked fine in sqlite. To fix this I had to create the database with utf8mb4 instead: create database microblog character set utf8mb4 collate utf8mb4_unicode_ci; I also had to add the charset to the end of the database url: DATABASE_URL=mysql+pymysql://:@localhost:3306/microblog?charset=utf8mb4

    I hope this helps someone dealing with errors that look like this: sqlalchemy.exc.InternalError: (pymysql.err.InternalError) (1366, "Incorrect string value: '\xF0\x9F\xA4\xA1\xF0\x9F...' for column 'body' at row 1") [SQL: 'INSERT INTO post (body, timestamp, user_id) VALUES (%(body)s, %(timestamp)s, %(user_id)s)'] [parameters: {'timestamp': datetime.datetime(2018, 12, 10, 5, 11, 3, 301048), 'body': '\U0001f921\U0001f921\U0001f921', 'user_id': 1}] (Background on this error at: http://sqlalche.me/e/2j85)

  • #104 hüseyin fahri uzun said 2018-12-18T15:40:36Z

    How do you run Elasticsearch? I mean i installed on ubuntu 18.04 but it won't run with an error of

    ConnectionError: ConnectionError(: Failed to establish a new connection: [Errno 111] Connection refused) caused by: NewConnectionError(: Failed to establish a new connection: [Errno 111] Connection refused).

    I guess i need to add 9200 port to nginx or something?

  • #105 Miguel Grinberg said 2018-12-18T16:24:58Z

    @hüseyin: there are several ways to install elasticsearch, my recommendation is that you follow the installation instructions at https://elastic.co for your platform. Also make sure that you install version 6 or newer, older versions are unlikely to work with this tutorial.

  • #106 Markus said 2019-01-06T19:19:41Z

    Hi Miguel,

    I have a question about the export variables in the shell.

    When I exported the variables in the shell: export MAIL_SERVER=smtp.gmail.com export MAIL_PORT=587 export MAIL_USE_TLS=1 export MAIL_USERNAME= export MAIL_PASSWORD= I can find them only if I don't close it. Otherwise they are lost.

    What should I do now? Should I write the date inside the ~/.profile? Can I write it inside the config.py? What is the recommanded way to keep password inside the memory longer than a shell session?

    Thanks in advance, Markus

  • #107 Miguel Grinberg said 2019-01-06T19:30:13Z

    @Markus: this is actually covered in this article. You can use a .env file to store and preserve your environment variables.

  • #108 Joseph Szymborski said 2019-01-11T04:12:44Z

    I would strongly suggest not to use UUIDs as secrets/passwords, as they are not guaranteed not to be predictable (more here https://security.stackexchange.com/a/157277).

    I would suggest something that uses cryptographically secure sources of randomness like the snippet below:

    python -c "import base64, os; print(base64.b32encode(os.urandom(20)).decode('utf8'))"

    Cheers, and thanks so much for the awesome tutorials!!

  • #109 Simon said 2019-01-26T19:34:11Z

    Just a note for the wary.

    When you install nginx it comes with a default web server configured in /etc/nginx/sites-available/default with a symbolic link to that config from /etc/nginx/sites-enabled/default

    In order for your site to be available the configuration for this default webserver needs to be removed from /etc/nginx/sites-enabled.

    Alternatively install your microblog configuration file in /etc/nginx/sites-available and create a symbolic link to it from /etc/nginx/sites-enabled/ and remove the default symbolic link.

  • #110 Miguel Grinberg said 2019-01-27T08:31:05Z

    @Simon: the tutorial instructs you to remove the default site configuration.

  • #111 Erick said 2019-02-22T12:43:54Z

    I already have a Ubuntu server with a web application using the LEMP stack and a Let's Encrypt SSL certificate on, let's say, tools.mysite.com/webapp. Is it possible to configure nginx so that I can deploy the microblog on tools.mysite.com/microblog using the same SSL certificate?

  • #112 Miguel Grinberg said 2019-02-22T16:44:01Z

    @Erick: yes, nginx provides a lot of flexibility in how you set up your base URLs. See the "location" statement in their documentation for details.

  • #113 Peter! said 2019-03-06T16:01:39Z

    Hey Miguel,

    This chapter is so cool, but I'm stuck on the last step -

    When I run 'sudo service nginx reload' I get the error 'nginx.service is not active, cannot reload.'

    I tried running sudo service nginx start' since that seemed logical, but again got an error

    'Job for nginx.service failed because the control process exited with error code. See "systemctl status nginx.service" and "journalctl -xe" for details.'

    Any ideas what might be going on?

    thanks!

  • #114 Miguel Grinberg said 2019-03-07T09:55:45Z

    @Peter: You need to follow the error message advice and check the logs with those commands. It is possible that you made a mistake in your nginx configuration so nginx is not starting.

  • #115 Mirko said 2019-03-30T15:51:43Z

    Hi Miguel, absolutely great tutorials, I have managed to go through them and locally everything works but when deployed (DigitalOcean droplet) some things work and some don't 1.) locally i have used .flaskenv for enviroment variables but when deploying i have created .env file with 'DATABASE_URL' set inside, it's still somehow uses sqlite db and stores data in it and for os.environ['DATABASE_URL'] i get None, so what is the proper way or alternative ways to set this env variable 2.) mail doesn't work, maybe it's the same problem with env variables. also i read that digital ocean disabled the support or restricted it somehow. how hard is to use something else, some external service 3.) api doesn't work remotely, locally it does, first i need to generate token then to use it (from terminal) but when i do the same thing from my local computer using domain name, it doesn't i get 301 "moved permanently" error

    I hope you can resolve some of the issues I have, and thanks for the tutorials (does book have more details?)

  • #116 Miguel Grinberg said 2019-03-30T16:53:10Z

    @Mirko: here are some ideas for the problems that you have: 1) if .flaskenv is imported, then the .env file should be imported too. If neither of them is imported, then make sure you have python-dotenv installed, and also that the current directory when you run the app is your top-level folder, i.e. where the .flaskenv and .env files are located. 2) DigitalOcean blocks SMTP connections on droplets in an attempt to prevent or reduce spam coming from their servers. I believe you can request that they unblock your droplet. 3) When you get the 301, you need to see what the value of the Location header is. The API is telling you that you are using the wrong URL and is sending you to the correct one. It could be that you are using http:// while you should be using https://. If you have nginx in your droplet, then the 301 might be coming from the nginx configuration and not from your app.

    Hope this gives you some ideas.

  • #117 Mirko said 2019-03-31T17:39:57Z

    @Miguel Thanks! Regarding 301, location header is https while i use http, also when i use http i get SSLError, is it maybe something with ssl setup that is wrong, I think i setup the certificates like in the article. Regarding reading of .env and .flaskenv files, it seems that it doesn't read either of those. I put logs in the login route to print me in the flash message what is the DATABASE_URL but it was always none, I tried exporting DATABASE_URL and it prints in the python interpreter correctly but it's still none when app is started. I tried set it up from venv and global, the same thing. I wonder what is going on, also I don't know how to make sure that current directory is top level folder, nginx starts that app in that folder if I have understood. Thanks for your answers, sorry for begginer mistakes!

  • #118 Miguel Grinberg said 2019-03-31T21:34:58Z

    @Mirko: so does the API work if you send https:// URLs? If you use a self-signed certificate you will get a validation error that you will need to tell your client to ignore. Regarding the config error, I can't really tell you what's wrong. You should look at my source code (downloadn and github links at the top of the article) and compare against yours to find the mistake.

  • #119 Mirko said 2019-04-01T18:17:50Z

    @Miguel: Yes! I managed to make it work by getting certificate from letsencrypt, browser doesn't complain for privacy if i use example.com and everything works fine but if i use www.example.com than it complains about privacy. this is the only thing left to complete the server setup. do you have any idea where to look?

    api works fine! thank you

  • #120 Miguel Grinberg said 2019-04-01T18:20:12Z

    @Mirko: the certificate needs to be for the main domain and any subdomains that you will use. Or you can get a wildcard certificate that applies to all subdomains.

  • #121 Mirko said 2019-04-02T20:02:54Z

    @Miguel, great I managed to get certificates to work, also emails work, i forgot to load .env file, i somehow missed the loading of the .env file :) I was playing with the deployed app, and everything worked, but i noticed that url is messed up i have example.com/main/index example.com/main/explore example.com/main/users etc...

    where to look for these kind of mistakes? thanks again!

  • #122 Miguel Grinberg said 2019-04-02T21:14:59Z

    @Mirko: are you using the same URLs that I'm using? The /main suggests you are using a URL prefix on the main blueprint.

  • #123 raylite said 2019-04-26T11:08:57Z

    Hi Miguel, Thank you for the detailed tutorials. I want to ask your guidance on the deployment issue. I have followed your tutorial and was able to successfully deploy on Ubuntu multiple times. However, I was faced now with a task of deploying on CENTOS 7. I discovered the placement of nginx files are a bit different. I have tried several work around with no luck. Would you be able to instruct on the things to do differently when deploying on CENTOS or point me to a useful site out there. Particularly, as it concerns the Nginx configuration.

    Thank you

  • #124 Miguel Grinberg said 2019-04-26T21:56:33Z

    @raylite: not aware of any major differences. I believe you don't get the /etc/nginx/sites-enabled/ directory like in Ubuntu, instead it is /etc/nginx/conf.d/, but other than it should work more or less the same. There are many guides on the Internet on deploying nginx on CentOS, I don't really use CentOS that much so I don't really remember having to do anything significantly different.

  • #125 Yuri Sales said 2019-05-06T13:53:01Z

    Everytime I run any flask db command, it execution never stops. Why is it happening?

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