Why Your Nginx Alias Returns Wrong MIME Types

The Problem

I had a simple nginx configuration using alias to serve media files:

http {
    server {
        location /media/ {
            alias /app/media/;
        }
    }
}

Everything seemed fine, but browsers were receiving the wrong Content-Type headers. Instead of image/png for images, nginx was serving everything as application/octet-stream or text/plain.

Including the MIME types configuration inside the server block fixes it:

http {
    server {
        include /etc/nginx/mime.types;
        
        location /media/ {
            alias /app/media/;
        }
    }
}

Why This Happens

The mime.types file contains the mapping between file extensions and their corresponding MIME types. While it’s often included at the http level in the main nginx configuration, if you’re working with a minimal config or the include is missing from your specific server block, nginx won’t know how to properly identify file types.

Without this mapping, nginx falls back to a default MIME type, which won’t work correctly for CSS, JavaScript, images, and other static assets.

The Takeaway

When using nginx alias (or root), always ensure mime.types is included at the http or server level. It’s one of those configurations that’s easy to overlook but critical for serving static files correctly.