Did you use any guide to create a custom Node.js application? What did you modify in the
/opt/bitnami/apache2/conf/bitnami/bitnami.conf config file?
It is not necessary to include any configuration in that file, you can create a custom file for the Apache configuration related to your application. You can find more information about how to create a new Node.js application on your Bitnami MEAN stack in our guide linked below
Apart from that, you can't use port 80 for your Express application because that is the port used by Apache. With the
ProxyPass configuration above, Apache will redirect requests on port 80 to the Express port 3000 and vice versa so you can access your application on port 80. Also, as mentioned in the guide, you will need to open port 3000 in Google Cloud to access it directly. You can find more information about it in the link below
Hope it helps,