nginx map location based on cookie (for when you want to test a site but give a static page to everyone else)

example.com.conf

# everyone, by default, will go to @underconstruction
# however, if you set cookienamehere=cookievaluehere, you get sent to @testbed instead

# by default, @under_construction shows static files from /var/www/under_construction
# by default, @testbed proxypasses to http://127.0.0.1:3000
# change those to do whatever youw ant

# if you want
# you can change $cookie_cookienamehere to $remote_addr and replace the "~cookievaluehere" with your ip
# that'll make it so that it's based on ip instead of cookie
# i just figured this is better since you can choose to see the construction page if you want

# please note that this is dependent on a file named "__THIS_FILE_SHOULD_NEVER_EXIST__" not existing
# if you create a file with that name idk what your issue is. just dont do that.
# (__THIS_FILE_SHOULD_NEVER_EXIST__ is required because nginx is weird about try_files)

# a nyway heres the code:

map $cookie_cookienamehere $end_to_use {
        default @under_construction;
        "~cookievaluehere" @testbed;
}

server {
        server_name example.com;
        index index.html index.htm;
        
        listen 80;
        
        location / {
                try_files /__THIS_FILE_SHOULD_NEVER_EXIST__ $end_to_use;
        }

        location @under_construction {
                root /var/www/under_construction;
                try_files $uri $uri/ =404;
        }
        location @testbed {
                proxy_pass http://127.0.0.1:3000;
                proxy_set_header Host $host;
                proxy_set_header X-Forwarded-For $remote_addr;
                proxy_set_header X-Forwarded-Proto https;
        }
}