If you are on the latest Exadata plugin for EM 13.3 (well, even the 13.2 version of the plugin). Be aware that there’s a bug where if the Exadata nodes’ names are longer than 7 characters, you cannot discover them.
EM just throws a weird error with below legend:
SEVERE: makeTargetsXml for each rack#: 1 e=java.lang.StringIndexOutOfBoundsException: String index out of range: -1
The solution is to apply the latest (March 2019) Bundle Patch to the agents running on the Exadata’s compute nodes.
More info on below MOS note:
Exadata Discovery Fails With "No New Component Is Discovered. Click Cancel" (Doc ID 2477624.1)
Another good excuse to keep your EM system up to date.