If no database connection could be made eZ Publish returns KERNEL_NOT_AVAILABLE error code.

Then KERNEL_NOT_AVAILABLE code causes 404 http error code for an end user.

But it is not correct to return 404 http error code for a database unavailability. 404 could provoke a website removal from a search engine index.
Correct http code is 503 (Service Unavailable) to inform a search engine about a temporary problem).

So, my proposal is to return KERNEL_NO_DB_CONNECTION in this case changing kernel/classes/eznodeviewfunctions.php

from

if ( !is_object( $node ) )
{
	return  array( 'content' => $Module->handleError( eZError::KERNEL_NOT_AVAILABLE, 'kernel' ),
				   'store'   => false );
}

to

if ( !is_object( $node ) )
{
	if ( !$db->isConnected())
	{
			   return  array( 'content' => $Module->handleError( eZError::KERNEL_NO_DB_CONNECTION, 'kernel' ),
							   'store'   => false );
	 
	}
	return  array( 'content' => $Module->handleError( eZError::KERNEL_NOT_AVAILABLE, 'kernel' ),
				   'store'   => false );
}

Steps to reproduce

1. Switch off the database
2. See eZ Publish error code and http error code