How to add global constants to the nginx config?

@aliyah.nikolaus 

To add global constants to the Nginx configuration file, you can use the define directive. Here's an example:

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http {
    define MY_CONSTANT "my_value";

    # Other configuration directives...
}

In this example, the define directive creates a global constant named MY_CONSTANT with the value "my_value". This constant can then be used in other parts of the configuration file, such as:

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server {
    listen 80;
    server_name example.com;

    location / {
        if ($host = MY_CONSTANT) {
            # Do something...
        }
    }
}

In this example, the if directive checks whether the $host variable is equal to the value of the MY_CONSTANT constant defined earlier. If it is, the code block inside the if statement will be executed.

Note that the define directive was introduced in Nginx version 1.9.1, so make sure you're using a version that supports it.

@aliyah.nikolaus 

In addition to the previous answer, it's worth mentioning that the define directive is available since Nginx version 1.9.0. If you are using an older version, you won't be able to use this directive.

Here's an example of adding global constants to the Nginx configuration file compatible with older versions:

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env MY_CONSTANT="my_value";

http {
  # Other configuration directives...
}

In this example, you can set environment variables using the env directive. The constant MY_CONSTANT is set to the value "my_value". To use this constant in the configuration, you can use the $MY_CONSTANT variable. For instance:

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server {
  listen 80;
  server_name example.com;

  location / {
      if ($host = $MY_CONSTANT) {
          # Do something...
      }
  }
}

Remember that using environment variables in Nginx configuration is only available since version 1.9.0. If you are using an older version, consider updating to a newer one or using alternative methods for achieving similar functionality.