[MUSIC] It's common for development teams to support a number of different application environments as a part of their development activities. Each of these environments might have a different configuration depending on the task that it's being optimized for. Let's start by considering the most common application environments for developers to work in. The development environment is the one configured for an individual developer's computer. This environment should be set up to make the developer's job as efficient as possible. In this environment, you don't want developers spending a lot of time configuring database servers and web servers, you want them writing the code that defines the application. Thus, you'd like the development environment to be set up to manage the mundane aspects of development, so that developers can focus on the novel aspects of the application they're building. The testing environment is set up to allow for testing of the application as a whole, and this could mangle the database. What I mean by this is that this database is set up to test the application's functionality and make sure the application does what it's supposed to do. So we often use fake data in this environment, it's loaded into the database prior to testing and then the database is destroyed after running these tests. The next is the staging environment. This mirrors the production environment that's used for final testing. You don't want to push your changes to the production environment when you're editing code without first testing that the changes work in an environment that mirrors the production environment. So with this environment, you're testing that the deployment itself works. Finally, there's the production environment itself. This is the one that the application will be deployed in. This is the environment that's used when you deploy your application for the world to use. Rails automatically set up applications to run in one of three prebuilt environments. And you can also create your own environments if you want to. The three that Rails provides include the development environment, and in this case, classes are loaded on every requests, so this is useful for debugging. Because of this, there's no need to restart the web server if you need to make edits to your model, viewer or controller code. You just make another web request and then the new classes are automatically loaded, the ones that you've edited. In addition, caching is turned off and there's a lot of debugging information that's rendered in the web page if an error is encountered. Rails also sets up a test environment, this includes a separate database. And automated tests that are applied to this database. So, the database is set up prior to testing and destroyed after testing is completed. The production environment that Rails sets up is optimized for delivery of assets to the client, when you're running in the production mode. It does this by turning on caching and handling errors more efficiently. By default, when you type rails server at the command line, it starts the application running in the development environment. So this is what we've done so far. If you'd like to start it in a different environment, type rails server -e, where the e stands for environment. You could also spell out environment and then describe the environment you want it to run in. So in this case, it would run in the production environment if I issued this command. Now the different environments are defined in the directory config of your Rails app, at the root of your Rails app. Look at config/environments and then you'll see three Ruby files, one for production, one for development and one for testing. Now, the different gems that are included in each environment are specified in the Gemfile. Let's take a look at these things in the blog application. I've opened up an operating system command line window at the root of my Rails blog app. And if I'd like to see information about the app itself, I can type rake about. And you'll see that it tells me right here that I'm running in the development environment. You can specify the Rails environment you want to run in when you execute rake or Rails commands. And here's how you do it, you type RAILS_ENV and then you specify the environment that you want to run in. And then the command you'd like to execute. So I'm going to execute the same one, rake about, but now I'm going to do it by running in the production environment. And you see it'll tell me about the same, except here it says that I'm running in the production environment. One more thing I'd like to show you. Open up IRB by doing rails console. And you can always find the development environment you're running in from within this console by typing Rails.env. And here it tells you that you're running in the development environment. In an editor, I've opened up my blog project, and if you go under the directory config, and then under the directory environments, you'll see three Ruby files. Let's take a look at the development one and you'll see all of the commands that are used to set up your development environment here. We can take a look at the production environment and you can read through all the comments there and see the differences between these environments. If you'd like to create your own environment, you could start by tweaking one of these environments and then store the new environment with a different name in this directory. Let me take a look at the gemfile next. At the top you'll see a list of gems that are going to get loaded into every environment, and then down here, there's a group command. And next to it, it says development and test. So the gems within this block will only be loaded into the development and test environments. I'm back in an operating system command line window. And I want to show you what happens when I type rails server. One thing I want to show you is you don't actually have to type out server. I can just say rails s and you'll see that it's going to open up the server, the web server in development mode. The entire environment, in fact, in development mode. I'm going to Ctrl+C out of this and I'm going to show you that I can do this in the production environment by typing rails s -e for environment and then production. And you'll see that the Rails application will now start up in production mode. Again, I'm going to Ctrl+C, and I could accomplish the same thing that I just did by typing RAILS_ENV as I showed you before, specifying that I'd like to run in the production environment and then just typing rails server again. And you'll see that in this case, it's going to, again, open up in the production environment. So, you've seen now how you can run Rails in a variety of different environments. And you've also seen how Rails is set up to configure the specific elements of those environments.
