i have odoo V 10
Cloud image on AWS using bitnami
with POS and Ecommerce apps already  installed

When try to install or uninstall a new odoo module(apps) i got a message with:

" Connection lost
Trying to reconnect... "

then i reload the page and this appears:

" Service Unavailable

The server is temporarily unable to service your request due to maintenance downtime or capacity problems. Please try again later.

Additionally, a 503 Service Unavailable error was encountered while trying to use an ErrorDocument to handle the request. "

i can make it work again by rebooting the instance on AWS (EC2 management console -> actions -> instance state -> reboot).

After the reboot, the app appears as installed at Apps, but no change was made. There is no new tab.
The same happens when i try to install an accounting configuration.
There is no new accounts.

How can i install new apps? or accounting packages?