If the database is temporary non available, let's say during a reboot of database services, Nuxeo DM will crash with this error on the UI :
If you can read this in your browser, this probably because of a configuration problem of your nuxeo.war/WEB-INF/pages.xml. To change this, edit the OSGI-INF/deployment-fragment.xml of your project at extension pages#PAGES.
Using the Tomcat Resource attribute validationQuery="SELECT 1" (for instance) solves the problem for the datasources but not for VCS.
The error in error-after-database-up-back.txt remains.