Consider using external Node's interfaces if internal are unavailable

[carpawell]

After #1667, there could be situations when the internal apps could not use other apps' internal interfaces.

That could be considered as one of:

1. App is unavailable, skip it;
2. App status is unknown and the caller should try an external interface as the best effort.

Choose and implement the option (or do nothing if the option says so).

[carpawell]

Closed via #1817.