为什么我要使用环境变量来配置Symfony应用程序？

Question

Yesterday was the first time I made a deploy in an own server with Symfony 4. Reading the official documentation about deployment, I quote:

Most Symfony applications read their configuration from environment variables. While developing locally, you'll usually store these in a .env file. But on production, instead of creating this file, you should set real environment variables.

Now, since I read on multiple sites that that's the correct way to work in production, I have several doubts about it:

• What is the meaning of environment variables in production? Why not just have the variables in a file like Wordpress, Django, and others?
• Why would I like have the credentials of my project's database in a global OS variable???
• Being globals and accessible by all in the OS, if I would have more than one project with the same env var (for instance, APP_ENV in Symfony), changing its value would affect all my projects! Does It make any sense?

If anyone could throw a little light on the subject, I would appreciate it very much.

Sorry about my English

Answer 1

This question is not a great fit for SO, but in brief: Environment variables can be set for any environment, not just the operating system. Like your web server, for example. I have the following in /etc/httpd/conf.d/variables.conf which is included into certain virtual hosts in my main Apache config:

#Config for web apps
SetEnv DB_CONNECTION      "mysql"
SetEnv DB_HOST            "192.168.242.1"
SetEnv DB_USERNAME        "dbuser"
SetEnv DB_PASSWORD        "dbpass"
SetEnv DB_DATABASE        "dbname"

This file can be protected with permissions to ensure only the web server itself can read them. And I can have multiple files, if I have multiple apps or virtual hosts.