If our app's inputs.conf uses an index other than "main" (e.g. a custom index for our app) does our app's setup UI (or the user via manual changes) need to create the index? Or will Splunk automatically create the index if it doesn't already exist?
A new index will not be created automatically as far as I know.
The indexes.conf needs to be configured to indicate a new index.
Some of the important properties in the stanza include
[<NAME_OF_INDEX>]
homePath = $SPLUNK_DB/<NAME_OF_INDEX>/db
coldPath = $SPLUNK_DB/<NAME_OF_INDEX>/colddb
thawedPath = $SPLUNK_DB/<NAME_OF_INDEX>/thaweddb
No it will not be created. Events sent to an unconfigured index will usually be discarded.
The error message will be shown in SplunkWeb when you restart Splunk telling you that the particular index is not configured or disabled.
Wolverine, do you see that message when events are being indexed and discarded, or whenever you setup an input with an undefined index?
At least in version 4.1.2 you'll now see a banner telling you that events are being sent to an unconfigured or disabled index.