The EC2 plugin is unable to successfully connect to any Eucalyptus 3.x cloud.

The EC2 plugin currently requests a single URL – [Eucalytpus_URL]/register – which it calls in order to obtain the EC2 and S3 endpoints. The trouble immediately hits when the EC2 plugin attempts to use the AWS Java SDK to connect to Eucalyptus. The specific issue is that the AWS Java SDK requires a trailing "/" to successfully connect. For example:
http://eucalyptus.mycloud.com/services/Eucalyptus
is what is returned from the /register call. But this:
http://eucalyptus.mycloud.com/services/Eucalyptus/
is what the SDK needs.

It should be noted that the /register endpoint is deprecated. Eucalyptus created that service call for a specific partner integration. The endpoint is no longer required by that partner and there are no plans to maintain it.

The resolution should ensure the EC2 plugin a) successfully connects and b) does not require the /register endpoint.