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      How To Serve Flask Applications with Gunicorn and Nginx on Ubuntu 18.04


      Introduction

      In this guide, you will build a Python application using the Flask microframework on Ubuntu 18.04. The bulk of this article will be about how to set up the Gunicorn application server and how to launch the application and configure Nginx to act as a front-end reverse proxy.

      Prerequisites

      Before starting this guide, you should have:

      • A server with Ubuntu 18.04 installed and a non-root user with sudo privileges. Follow our initial server setup guide for guidance.
      • Nginx installed, following Steps 1 and 2 of How To Install Nginx on Ubuntu 18.04.
      • A domain name configured to point to your server. You can purchase one on Namecheap or get one for free on Freenom. You can learn how to point domains to DigitalOcean by following the relevant documentation on domains and DNS. Be sure to create the following DNS records:

        • An A record with your_domain pointing to your server’s public IP address.
        • An A record with www.your_domain pointing to your server’s public IP address.
      • Familiarity with the WSGI specification, which the Gunicorn server will use to communicate with your Flask application. This discussion covers WSGI in more detail.

      Step 1 — Installing the Components from the Ubuntu Repositories

      Our first step will be to install all of the pieces we need from the Ubuntu repositories. This includes pip, the Python package manager, which will manage our Python components. We will also get the Python development files necessary to build some of the Gunicorn components.

      First, let’s update the local package index and install the packages that will allow us to build our Python environment. These will include python3-pip, along with a few more packages and development tools necessary for a robust programming environment:

      • sudo apt update
      • sudo apt install python3-pip python3-dev build-essential libssl-dev libffi-dev python3-setuptools

      With these packages in place, let’s move on to creating a virtual environment for our project.

      Step 2 — Creating a Python Virtual Environment

      Next, we’ll set up a virtual environment in order to isolate our Flask application from the other Python files on the system.

      Start by installing the python3-venv package, which will install the venv module:

      • sudo apt install python3-venv

      Next, let’s make a parent directory for our Flask project. Move into the directory after you create it:

      • mkdir ~/myproject
      • cd ~/myproject

      Create a virtual environment to store your Flask project’s Python requirements by typing:

      • python3.6 -m venv myprojectenv

      This will install a local copy of Python and pip into a directory called myprojectenv within your project directory.

      Before installing applications within the virtual environment, you need to activate it. Do so by typing:

      • source myprojectenv/bin/activate

      Your prompt will change to indicate that you are now operating within the virtual environment. It will look something like this: (myprojectenv)user@host:~/myproject$.

      Step 3 — Setting Up a Flask Application

      Now that you are in your virtual environment, you can install Flask and Gunicorn and get started on designing your application.

      First, let’s install wheel with the local instance of pip to ensure that our packages will install even if they are missing wheel archives:

      Note


      Regardless of which version of Python you are using, when the virtual environment is activated, you should use the pip command (not pip3).

      Next, let's install Flask and Gunicorn:

      • pip install gunicorn flask

      Creating a Sample App

      Now that you have Flask available, you can create a simple application. Flask is a microframework. It does not include many of the tools that more full-featured frameworks might, and exists mainly as a module that you can import into your projects to assist you in initializing a web application.

      While your application might be more complex, we'll create our Flask app in a single file, called myproject.py:

      • nano ~/myproject/myproject.py

      The application code will live in this file. It will import Flask and instantiate a Flask object. You can use this to define the functions that should be run when a specific route is requested:

      ~/myproject/myproject.py

      from flask import Flask
      app = Flask(__name__)
      
      @app.route("/")
      def hello():
          return "<h1 style='color:blue'>Hello There!</h1>"
      
      if __name__ == "__main__":
          app.run(host='0.0.0.0')
      

      This basically defines what content to present when the root domain is accessed. Save and close the file when you're finished.

      If you followed the initial server setup guide, you should have a UFW firewall enabled. To test the application, you need to allow access to port 5000:

      Now you can test your Flask app by typing:

      You will see output like the following, including a helpful warning reminding you not to use this server setup in production:

      Output

      * Serving Flask app "myproject" (lazy loading) * Environment: production WARNING: Do not use the development server in a production environment. Use a production WSGI server instead. * Debug mode: off * Running on http://0.0.0.0:5000/ (Press CTRL+C to quit)

      Visit your server's IP address followed by :5000 in your web browser:

      http://your_server_ip:5000
      

      You should see something like this:

      Flask sample app

      When you are finished, hit CTRL-C in your terminal window to stop the Flask development server.

      Creating the WSGI Entry Point

      Next, let's create a file that will serve as the entry point for our application. This will tell our Gunicorn server how to interact with the application.

      Let's call the file wsgi.py:

      In this file, let's import the Flask instance from our application and then run it:

      ~/myproject/wsgi.py

      from myproject import app
      
      if __name__ == "__main__":
          app.run()
      

      Save and close the file when you are finished.

      Step 4 — Configuring Gunicorn

      Your application is now written with an entry point established. We can now move on to configuring Gunicorn.

      Before moving on, we should check that Gunicorn can serve the application correctly.

      We can do this by simply passing it the name of our entry point. This is constructed as the name of the module (minus the .py extension), plus the name of the callable within the application. In our case, this is wsgi:app.

      We'll also specify the interface and port to bind to so that the application will be started on a publicly available interface:

      • cd ~/myproject
      • gunicorn --bind 0.0.0.0:5000 wsgi:app

      You should see output like the following:

      Output

      [2018-07-13 19:35:13 +0000] [28217] [INFO] Starting gunicorn 19.9.0 [2018-07-13 19:35:13 +0000] [28217] [INFO] Listening at: http://0.0.0.0:5000 (28217) [2018-07-13 19:35:13 +0000] [28217] [INFO] Using worker: sync [2018-07-13 19:35:13 +0000] [28220] [INFO] Booting worker with pid: 28220

      Visit your server's IP address with :5000 appended to the end in your web browser again:

      http://your_server_ip:5000
      

      You should see your application's output:

      Flask sample app

      When you have confirmed that it's functioning properly, press CTRL-C in your terminal window.

      We're now done with our virtual environment, so we can deactivate it:

      Any Python commands will now use the system's Python environment again.

      Next, let's create the systemd service unit file. Creating a systemd unit file will allow Ubuntu's init system to automatically start Gunicorn and serve the Flask application whenever the server boots.

      Create a unit file ending in .service within the /etc/systemd/system directory to begin:

      • sudo nano /etc/systemd/system/myproject.service

      Inside, we'll start with the [Unit] section, which is used to specify metadata and dependencies. Let's put a description of our service here and tell the init system to only start this after the networking target has been reached:

      /etc/systemd/system/myproject.service

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

      Next, let's open up the [Service] section. This will specify the user and group that we want the process to run under. Let's give our regular user account ownership of the process since it owns all of the relevant files. Let's also give group ownership to the www-data group so that Nginx can communicate easily with the Gunicorn processes. Remember to replace the username here with your username:

      /etc/systemd/system/myproject.service

      [Unit]
      Description=Gunicorn instance to serve myproject
      After=network.target
      
      [Service]
      User=sammy
      Group=www-data
      

      Next, let's map out the working directory and set the PATH environmental variable so that the init system knows that the executables for the process are located within our virtual environment. Let's also specify the command to start the service. This command will do the following:

      • Start 3 worker processes (though you should adjust this as necessary)
      • Create and bind to a Unix socket file, myproject.sock, within our project directory. We'll set an umask value of 007 so that the socket file is created giving access to the owner and group, while restricting other access
      • Specify the WSGI entry point file name, along with the Python callable within that file (wsgi:app)

      Systemd requires that we give the full path to the Gunicorn executable, which is installed within our virtual environment.

      Remember to replace the username and project paths with your own information:

      /etc/systemd/system/myproject.service

      [Unit]
      Description=Gunicorn instance to serve myproject
      After=network.target
      
      [Service]
      User=sammy
      Group=www-data
      WorkingDirectory=/home/sammy/myproject
      Environment="PATH=/home/sammy/myproject/myprojectenv/bin"
      ExecStart=/home/sammy/myproject/myprojectenv/bin/gunicorn --workers 3 --bind unix:myproject.sock -m 007 wsgi:app
      

      Finally, let's add an [Install] section. This will tell systemd what to link this service to if we enable it to start at boot. We want this service to start when the regular multi-user system is up and running:

      /etc/systemd/system/myproject.service

      [Unit]
      Description=Gunicorn instance to serve myproject
      After=network.target
      
      [Service]
      User=sammy
      Group=www-data
      WorkingDirectory=/home/sammy/myproject
      Environment="PATH=/home/sammy/myproject/myprojectenv/bin"
      ExecStart=/home/sammy/myproject/myprojectenv/bin/gunicorn --workers 3 --bind unix:myproject.sock -m 007 wsgi:app
      
      [Install]
      WantedBy=multi-user.target
      

      With that, our systemd service file is complete. Save and close it now.

      We can now start the Gunicorn service we created and enable it so that it starts at boot:

      • sudo systemctl start myproject
      • sudo systemctl enable myproject

      Let's check the status:

      • sudo systemctl status myproject

      You should see output like this:

      Output

      ● myproject.service - Gunicorn instance to serve myproject Loaded: loaded (/etc/systemd/system/myproject.service; enabled; vendor preset: enabled) Active: active (running) since Fri 2018-07-13 14:28:39 UTC; 46s ago Main PID: 28232 (gunicorn) Tasks: 4 (limit: 1153) CGroup: /system.slice/myproject.service ├─28232 /home/sammy/myproject/myprojectenv/bin/python3.6 /home/sammy/myproject/myprojectenv/bin/gunicorn --workers 3 --bind unix:myproject.sock -m 007 ├─28250 /home/sammy/myproject/myprojectenv/bin/python3.6 /home/sammy/myproject/myprojectenv/bin/gunicorn --workers 3 --bind unix:myproject.sock -m 007 ├─28251 /home/sammy/myproject/myprojectenv/bin/python3.6 /home/sammy/myproject/myprojectenv/bin/gunicorn --workers 3 --bind unix:myproject.sock -m 007 └─28252 /home/sammy/myproject/myprojectenv/bin/python3.6 /home/sammy/myproject/myprojectenv/bin/gunicorn --workers 3 --bind unix:myproject.sock -m 007

      If you see any errors, be sure to resolve them before continuing with the tutorial.

      Step 5 — Configuring Nginx to Proxy Requests

      Our Gunicorn application server should now be up and running, waiting for requests on the socket file in the project directory. Let's now configure Nginx to pass web requests to that socket by making some small additions to its configuration file.

      Begin by creating a new server block configuration file in Nginx's sites-available directory. Let's call this myproject to keep in line with the rest of the guide:

      • sudo nano /etc/nginx/sites-available/myproject

      Open up a server block and tell Nginx to listen on the default port 80. Let's also tell it to use this block for requests for our server's domain name:

      /etc/nginx/sites-available/myproject

      server {
          listen 80;
          server_name your_domain www.your_domain;
      }
      

      Next, let's add a location block that matches every request. Within this block, we'll include the proxy_params file that specifies some general proxying parameters that need to be set. We'll then pass the requests to the socket we defined using the proxy_pass directive:

      /etc/nginx/sites-available/myproject

      server {
          listen 80;
          server_name your_domain www.your_domain;
      
          location / {
              include proxy_params;
              proxy_pass http://unix:/home/sammy/myproject/myproject.sock;
          }
      }
      

      Save and close the file when you're finished.

      To enable the Nginx server block configuration you've just created, link the file to the sites-enabled directory:

      • sudo ln -s /etc/nginx/sites-available/myproject /etc/nginx/sites-enabled

      With the file in that directory, you can test for syntax errors:

      If this returns without indicating any issues, restart the Nginx process to read the new configuration:

      • sudo systemctl restart nginx

      Finally, let's adjust the firewall again. We no longer need access through port 5000, so we can remove that rule. We can then allow full access to the Nginx server:

      • sudo ufw delete allow 5000
      • sudo ufw allow 'Nginx Full'

      You should now be able to navigate to your server's domain name in your web browser:

      http://your_domain
      

      You should see your application's output:

      Flask sample app

      If you encounter any errors, trying checking the following:

      • sudo less /var/log/nginx/error.log: checks the Nginx error logs.
      • sudo less /var/log/nginx/access.log: checks the Nginx access logs.
      • sudo journalctl -u nginx: checks the Nginx process logs.
      • sudo journalctl -u myproject: checks your Flask app's Gunicorn logs.

      Step 6 — Securing the Application

      To ensure that traffic to your server remains secure, let's get an SSL certificate for your domain. There are multiple ways to do this, including getting a free certificate from Let's Encrypt, generating a self-signed certificate, or buying one from another provider and configuring Nginx to use it by following Steps 2 through 6 of  How to Create a Self-signed SSL Certificate for Nginx in Ubuntu 18.04. We will go with option one for the sake of expediency.

      First, add the Certbot Ubuntu repository:

      • sudo add-apt-repository ppa:certbot/certbot

      You'll need to press ENTER to accept.

      Install Certbot's Nginx package with apt:

      • sudo apt install python-certbot-nginx

      Certbot provides a variety of ways to obtain SSL certificates through plugins. The Nginx plugin will take care of reconfiguring Nginx and reloading the config whenever necessary. To use this plugin, type the following:

      • sudo certbot --nginx -d your_domain -d www.your_domain

      This runs certbot with the --nginx plugin, using -d to specify the names we'd like the certificate to be valid for.

      If this is your first time running certbot, you will be prompted to enter an email address and agree to the terms of service. After doing so, certbot will communicate with the Let's Encrypt server, then run a challenge to verify that you control the domain you're requesting a certificate for.

      If that's successful, certbot will ask how you'd like to configure your HTTPS settings:

      Output

      Please choose whether or not to redirect HTTP traffic to HTTPS, removing HTTP access. ------------------------------------------------------------------------------- 1: No redirect - Make no further changes to the webserver configuration. 2: Redirect - Make all requests redirect to secure HTTPS access. Choose this for new sites, or if you're confident your site works on HTTPS. You can undo this change by editing your web server's configuration. ------------------------------------------------------------------------------- Select the appropriate number [1-2] then [enter] (press 'c' to cancel):

      Select your choice then hit ENTER. The configuration will be updated, and Nginx will reload to pick up the new settings. certbot will wrap up with a message telling you the process was successful and where your certificates are stored:

      Output

      IMPORTANT NOTES: - Congratulations! Your certificate and chain have been saved at: /etc/letsencrypt/live/your_domain/fullchain.pem Your key file has been saved at: /etc/letsencrypt/live/your_domain/privkey.pem Your cert will expire on 2018-07-23. To obtain a new or tweaked version of this certificate in the future, simply run certbot again with the "certonly" option. To non-interactively renew *all* of your certificates, run "certbot renew" - Your account credentials have been saved in your Certbot configuration directory at /etc/letsencrypt. You should make a secure backup of this folder now. This configuration directory will also contain certificates and private keys obtained by Certbot so making regular backups of this folder is ideal. - If you like Certbot, please consider supporting our work by: Donating to ISRG / Let's Encrypt: https://letsencrypt.org/donate Donating to EFF: https://eff.org/donate-le

      If you followed the Nginx installation instructions in the prerequisites, you will no longer need the redundant HTTP profile allowance:

      • sudo ufw delete allow 'Nginx HTTP'

      To verify the configuration, navigate once again to your domain, using https://:

      https://your_domain
      

      You should see your application output once again, along with your browser's security indicator, which should indicate that the site is secured.

      Conclusion

      In this guide, you created and secured a simple Flask application within a Python virtual environment. You created a WSGI entry point so that any WSGI-capable application server can interface with it, and then configured the Gunicorn app server to provide this function. Afterwards, you created a systemd service file to automatically launch the application server on boot. You also created an Nginx server block that passes web client traffic to the application server, relaying external requests, and secured traffic to your server with Let's Encrypt.

      Flask is a very simple, but extremely flexible framework meant to provide your applications with functionality without being too restrictive about structure and design. You can use the general stack described in this guide to serve the flask applications that you design.



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      How To Install Ruby on Rails with rbenv on Ubuntu 18.04


      Introduction

      Ruby on Rails is one of the most popular application stacks for developers looking to create sites and web apps. The Ruby programming language, combined with the Rails development framework, makes app development simple.

      You can easily install Ruby and Rails with the command-line tool rbenv. Using rbenv will provide you with a solid environment for developing your Ruby on Rails applications as it will let you easily switch Ruby versions, keeping your entire team on the same version.

      rbenv provides support for specifying application-specific versions of Ruby, lets you change the global Ruby for each user, and allows you to use an environment variable to override the Ruby version.

      This tutorial will take you through the Ruby and Rails installation process via rbenv.

      Prerequisites

      To follow this tutorial, you need:

      Step 1 – Install rbenv and Dependencies

      Ruby relies on several packages which you can install through your package manager. Once those are installed, you can install rbenv and use it to install Ruby,

      First, update your package list:

      Next, install the dependencies required to install Ruby:

      • sudo apt install autoconf bison build-essential libssl-dev libyaml-dev libreadline6-dev zlib1g-dev libncurses5-dev libffi-dev libgdbm5 libgdbm-dev

      Once the dependencies download, you can install rbenv itself. Clone the rbenv repository from GitHub into the directory ~/.rbenv:

      • git clone https://github.com/rbenv/rbenv.git ~/.rbenv

      Next, add ~/.rbenv/bin to your $PATH so that you can use the rbenv command line utility. Do this by altering your ~/.bashrc file so that it affects future login sessions:

      • echo 'export PATH="$HOME/.rbenv/bin:$PATH"' >> ~/.bashrc

      Then add the command ~/.rbenv/bin/rbenv init to your ~/.basrc file so rbenv loads automatically:

      • echo 'eval "$(rbenv init -)"' >> ~/.bashrc

      Next, apply the changes you made to your ~/.bashrc file to your current shell session:

      Verify that rbenv is set up properly by using the type command, which will display more information about the rbenv command:

      Your terminal window will display the following:

      Output

      rbenv is a function rbenv () { local command; command="${1:-}"; if [ "$#" -gt 0 ]; then shift; fi; case "$command" in rehash | shell) eval "$(rbenv "sh-$command" "$@")" ;; *) command rbenv "$command" "$@" ;; esac }

      Next, install the ruby-build, plugin. This plugin adds therbenv install command, which simplifies the installation process for new versions of Ruby:

      • git clone https://github.com/rbenv/ruby-build.git ~/.rbenv/plugins/ruby-build

      At this point, you have both rbenv and ruby-build installed. Let's install Ruby next.

      Step 2 – Installing Ruby with ruby-build

      With the ruby-build plugin now installed, you can install versions of Ruby y may need through a simple command. First, let's list all the available versions of Ruby:

      The output of that command should be a long list of versions that you can choose to install.

      Let's install Ruby 2.5.1:

      Installing Ruby can be a lengthy process, so be prepared for the installation to take some time to complete.

      Once it's done installing, set it asy our default version of Ruby with the global sub-command:

      Verify that Ruby was properly installed by checking its version number:

      If you installed version 2.5.1 of Ruby, your output to the above command should look something like this:

      Output

      ruby 2.5.1p57 (2018-03-29 revision 63029) [x86_64-linux]

      To install and use a different version of Ruby, run the rbenv commands with a different version number, as in rbenv install 2.3.0 and rbenv global 2.3.0.

      You now have at least one version of Ruby installed and have set your default Ruby version. Next, we will set up gems and Rails.

      Step 3 – Working with Gems

      Gems are the way Ruby libraries are distributed. You use the gem command to manage these gems. We'll use this command to install Rails.

      When you install a gem, the installation process generates local documentation. This can add a significant amount of time to each gem's installation process, so turn off local documentation generation by creating a file called ~/.gemrc which contains a configuration setting to turn off this feature:

      • echo "gem: --no-document" > ~/.gemrc

      Bundler is a tool that manages gem dependencies for projects. Install the Bundler gem next. as Rails depends on it.

      You'll see output like this:

      Output

      Fetching: bundler-1.16.2.gem (100%) Successfully installed bundler-1.16.2 1 gem installed

      You can use the gem env command (the subcommand env is short for environment) to learn more about the environment and configuration of gems. You can see where gems are being installed by using the home argument, like this:

      You'll see output similar to this:

      /home/sammy/.rbenv/versions/2.5.1/lib/ruby/gems/2.5.0
      

      Once you have gems set up, you can install Rails.

      Step 4 – Installing Rails

      To install the most recent version of Rails, use the gem install command:

      The gem command installs the gem you specify, as well as every dependency. Rails is a complex web development framework and has many dependencies, so the process will take some time to complete. Eventually you'll see a message stating that Rails is installed. along with its dependencies:

      Output

      ... Successfully installed rails-5.2.0 38 gems installed

      Note: If you would like to install a specific version of Rails, you can list the valid versions of Rails by doing a search, which will output a long list of possible versions. We can then install a specific version, such as 4.2.7:

      • gem search '^rails$' --all
      • gem install rails -v 4.2.7

      rbenv works by creating a directory of shims, which point to the files used by the Ruby version that's currently enabled. Through the rehash sub-command, rbenv maintains shims in that directory to match every Ruby command across every installed version of Ruby on your server. Whenever you install a new version of Ruby or a gem that provides commands, like Rails does, you should run:

      Verify that Rails has been installed properly by printing its version, with this command:

      If it installed properly, you will see the version of Rails that was installed:

      Output

      Rails 5.2.0

      At this point, you can begin testing your Ruby on Rails installation and start to develop web applications. Let's look at keeping rbenv up to date.

      Step 5 – Updating rbenv

      Since you installed rbenv manually using Git, you can upgrade your installation to the most recent version at any time by using the git pull command in the ~/.rbenv directory:

      This will ensure that we are using the most up-to-date version of rbenv available.

      Step 6 – Uninstalling Ruby versions

      As you download additional versions of Ruby, you may accumulate more versions than you would like in your ~/.rbenv/versions directory. Use the ruby-buildplugin 's' uninstall subcommand to remove these previous versions.

      For example, typing this will uninstall Ruby version 2.1.3:

      With the rbenv uninstall command you can clean up old versions of Ruby so that you do not have more installed than you are currently using.

      Step 7 – Uninstalling rbenv

      If you've decided you no longer want to use rbenv, you can remove it from your system.

      To do this, first open your ~/.bashrc file in your editor:

      Find and remove the following two lines from the file:

      ~/.bashrc

      ...
      export PATH="$HOME/.rbenv/bin:$PATH"
      eval "$(rbenv init -)"
      

      Save the file and exit the editor.

      Then remove rbenv and all installed Ruby versions with this command:

       rm -rf `rbenv root`
      

      Log out and back in to apply the changes to your shell.

      Conclusion

      In this tutorial you installed rbenv and Ruby on Rails. From here, you can learn more about making those environments more robust.

      Explore how to use Ruby on Rails with PostgreSQL or MySQL rather than its default sqlite3 database, which provide more scalability, centralization, and stability for your applications. As your needs grow, you can also learn how to scale Ruby on Rails applications across multiple servers.



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      How To Install Ruby on Rails with RVM on Ubuntu 18.04


      Introduction

      A popular web application framework, Ruby on Rails was designed to help you develop successful projects while writing less code. With an aim to making web development fun and supported by a robust community, Ruby on Rails is open-source software that is free to use and welcomes contributions to make it better.

      The command-line tool RVM (Ruby Version Manager) provides you with a solid development environment. RVM will let you manage and work with multiple Ruby environments and allow you to switch between them. The project repository is located in a git repository.

      This tutorial will take you through the Ruby and Rails installation process and set up via RVM

      Prerequisites

      This tutorial will take you through the Ruby on Rails installation process via RVM. To follow this tutorial, you need a non-root user with sudo privileges on an Ubuntu 18.04 server.

      To learn how to achieve this setup, follow our manual initial server setup guide or run our automated script.

      Installation

      The quickest way of installing Ruby on Rails with RVM is to run the following commands.

      We first need to update GPG, which stands for GNU Privacy Guard, to the most recent version in order to contact a public key server and request a key associated with the given ID.

      We are using a user with sudo privileges to update here, but the rest of the commands can be done by a regular user.

      Now, we’ll be requesting the RVM project’s key to sign each RVM release. Having the RVM project’s public key allows us to verify the legitimacy of the RVM release we will be downloading, which is signed with the matching private key.

      • gpg2 --keyserver hkp://keys.gnupg.net --recv-keys 409B6B1796C275462A1703113804BB82D39DC0E3 7D2BAF1CF37B13E2069D6956105BD0E739499BDB

      Let’s now move into a writable location such as the /tmp directory and then download the RVM script into a file:

      We'll use the curl command to download the RVM installation script from the project's website. The backslash that leads the command ensures that we are using the regular curl command and not any altered, aliased version.

      We will append the -s flag to indicate that the utility should operate in silent mode along with the -S flag to override some of this to allow curl to output errors if it fails. The -L flag tells the utility to follow redirects, and finally the -o flag indicates to write output to a file instead of standard output.

      Putting all of these elements together, our full command will look like this:

      • curl -sSL https://get.rvm.io -o rvm.sh

      Once it is downloaded, if you would like to audit the contents of the script before applying it, run:

      Then we can pipe it to bash to install the latest stable Rails version which will also pull in the associated latest stable release of Ruby.

      • cat /tmp/rvm.sh | bash -s stable --rails

      During the installation process, you may be prompted for your regular user’s password. When the installation is complete, source the RVM scripts from the directory they were installed, which will typically be in your home/username directory.

      • source /home/sammy/.rvm/scripts/rvm

      You should now have a full Ruby on Rails environment configured.

      Installing Specific Ruby and Rails Versions

      If you need to install a specific version of Ruby for your application, rather than just the most recent one, you can do so with RVM. First, check to see which versions of Ruby are available by listing them:

      Then, install the specific version of Ruby that you need through RVM, where ruby_version can be typed as ruby-2.4.0, for instance, or just 2.4.0:

      After the installation, we can list the available Ruby versions we have installed by typing:

      We can switch between the Ruby versions by typing:

      Since Rails is a gem, we can also install various versions of Rails by using the gem command. Let’s first list the valid versions of Rails by doing a search:

      • gem search '^rails$' --all

      Next, we can install our required version of Rails. Note that rails_version will only refer to the version number, as in 5.1.6.

      • gem install rails -v rails_version

      We can use various Rails versions with each Ruby by creating gemsets and then installing Rails within those using the normal gem commands.

      To create a gemset we will use:

      • rvm gemset create gemset_name

      To specify a Ruby version to use when creating a gemset, use:

      • rvm ruby_version@gemset_name --create

      The gemsets allow us to have self-contained environments for gems as well as have multiple environments for each version of Ruby that we install.

      Install JavaScript Runtime

      A few Rails features, such as the Asset Pipeline, depend on a JavaScript Runtime. We will install Node.js with the package manager apt to provide this functionality.

      Like we did with the RVM script, we can move to a writable directory, verify the Node.js script by outputting it to a file, then read it with less:

      • cd /tmp
      • curl -sSL https://deb.nodesource.com/setup_10.x -o nodejs.sh
      • less nodejs.sh

      Once we are satisfied with the Node.js script, we can install the NodeSource Node.js v10.x repo:

      • cat /tmp/nodejs.sh | sudo -E bash -

      The -E flag used here will preserve the user's existing environment variables.

      Now we can update apt and use it to install Node.js:

      • sudo apt update
      • sudo apt install -y nodejs

      At this point, you can begin testing your Ruby on Rails installation and start to develop web applications.

      How To Uninstall RVM

      If you no longer wish to use RVM, you can uninstall it by first removing the script calls in your .bashrc file and then removing the RVM files.

      First, remove the script calls with a text editor like nano:

      Scroll down to where you see the RVM lines of your file:

      ~/.bashrc

      ...
      # Add RVM to PATH for scripting. Make sure this is the last PATH variable change.
      export PATH="$PATH:$HOME/.rvm/bin"
      

      Delete the lines, then save and close the file.

      Next, remove RVM with the following command:

      At this point, you no longer have an

      Conclusion

      We have covered the basics of how to install RVM and Ruby on Rails here so that you can use multiple Ruby environments.

      For your next steps, you can learn more about working with RVM and how to use RVM to manage your Ruby installations.

      If you’re new to Ruby, you can learn about programming in Ruby by following our How To Code in Ruby tutorial series.

      For more scalability, centralization, and control in your Ruby on Rails application, you may want to use it with PostgreSQL or MySQL rather than its default sqlite3 database. As your needs grow, you can also learn how to scale Ruby on Rails applications across multiple servers.



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