hassio-addons/browser_chromium/rootfs/etc/nginx/sites-available/devtools.conf

# Chrome devtools: the browser only binds 127.0.0.1 when not headless,
# so expose it on 9221 through nginx (enabled by 90-ingress.sh when mapped)
server {
    listen 9221;

    location / {
        proxy_pass http://127.0.0.1:9222;
        proxy_http_version 1.1;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection "upgrade";
        proxy_set_header Host $http_host;
        proxy_read_timeout 86400s;
        proxy_send_timeout 86400s;
    }
}