I have an application using angular and nodejs for the frontend.
I have integrated a chat app using socket.io for nodejs, in my localhost it works fine.
For the deployment, I have configured two subdomains one for the backend and the other for the angular app to communicate safely.
I have added an SSL Certificate for the backend subdomain “backendapi.app.com” and the subdomain for the app “backoffice.app.com” .
I have doing that to configure cors and access api via frontend with safely mode and all works fine.
When I deployed my new version with the chat app, an error showed on the console :
GET https://backendapi.app.com/socket.io/?EIO=4&transport=polling&t=P7SX7Ir

My apache file for the backendapi.app.conf is :

<VirtualHost *:80>
    ServerName backendapi.app.com
    ServerAdmin webmaster@localhost

    DocumentRoot /var/www/html

    <Directory /var/www/html>
        Options Indexes FollowSymLinks
        AllowOverride All
        Require all granted
    </Directory>

    # Configuration du proxy inverse pour les API
    ProxyPreserveHost On
    ProxyPass /api http://127.0.0.1:3000/api
    ProxyPassReverse /api http://127.0.0.1:3000/api

    # Configuration du proxy pour les WebSockets
    ProxyPass /socket.io/ http://127.0.0.1:3000/socket.io/
    ProxyPassReverse /socket.io/ http://127.0.0.1:3000/socket.io/

    # En-têtes CORS et gestion des requêtes OPTIONS pour les WebSockets
    <Location /socket.io>
        Header always set Access-Control-Allow-Origin "https://backoffice.app.com"
        Header always set Access-Control-Allow-Methods "GET, POST, OPTIONS"
        Header always set Access-Control-Allow-Headers "Origin, Content-Type, Accept, Authorization"
        Header always set Access-Control-Allow-Credentials "true"
    </Location>

    # Logs
    ErrorLog ${APACHE_LOG_DIR}/backendapi_app_error.log
    CustomLog ${APACHE_LOG_DIR}/backendapi_app_access.log combined

    # Redirection HTTP vers HTTPS
    RewriteEngine on
    RewriteCond %{SERVER_NAME} =backendapi.app.com
    RewriteRule ^ https://%{SERVER_NAME}%{REQUEST_URI} [END,NE,R=permanent]
</VirtualHost>

and the with the SSL :

<IfModule mod_ssl.c>
<VirtualHost *:443>
    ServerName backendapi.app.com
    ServerAdmin webmaster@localhost

    DocumentRoot /var/www/html

    <Directory /var/www/html>
        Options Indexes FollowSymLinks
        AllowOverride All
        Require all granted
 # Configuration CORS
        Header set Access-Control-Allow-Origin "*"
        Header set Access-Control-Allow-Methods "GET, POST, PUT, DELETE, OPTIONS"
        Header set Access-Control-Allow-Headers "Content-Type,  Authorization"
    </Directory>

    # Configuration du proxy inverse
    ProxyPreserveHost On
    ProxyPass /api http://127.0.0.1:3000/api
    ProxyPassReverse /api http://127.0.0.1:3000/api



    # En-têtes CORS 
    <Location /api>
        Header set Access-Control-Allow-Origin "*"
        Header set Access-Control-Allow-Methods "GET, POST, PUT, DELETE, OPTIONS"
        Header set Access-Control-Allow-Headers "Origin, Content-Type, Accept, Authorization"
    </Location>


# En-têtes CORS pour les WebSockets
    <Location /socket.io>
        Header always set Access-Control-Allow-Origin "https://backoffice.app.com"
        Header always set Access-Control-Allow-Methods "GET, POST, OPTIONS"
        Header always set Access-Control-Allow-Headers "Origin, Content-Type, Accept, Authorization"
        Header always set Access-Control-Allow-Credentials "true"
    </Location>

    ErrorLog ${APACHE_LOG_DIR}/backendapi_app_error.log
    CustomLog ${APACHE_LOG_DIR}/backendapi_app_access.log combined

SSLCertificateFile /etc/letsencrypt/live/backendapi.app.com/fullchain.pem
SSLCertificateKeyFile /etc/letsencrypt/live/backendapi.app.com/privkey.pem
Include /etc/letsencrypt/options-ssl-apache.conf
</VirtualHost>
</IfModule>