Nexus Professional is licensed by user count, not the number of server instances. As long as the number of users accessing all Nexus instances per organization doesn't exceed the number in your written license agreement you are in compliance. Note that this is not a concurrent user count, it is a total user count.
For reference, the definition of "user" in the license agreement is:
A "User" means any person who accesses Nexus Professional, either directly via the Nexus Professional UI or via various plugins, or who may access or use the artifacts hosted by Nexus Professional whether directly or through proxied or replicated repositories. This includes administrators who submit content to, retrieve content from, or in any other way interact with Nexus Professional.
Q. I want to set up a test Nexus instance. Do the number of licensed users apply to this test instance.
Q. Does a user token for the same physical user as a username identifier equate to a single licensed user?
A. Yes. We treat these as multiple ids for the same licensed user.
Q. Does anonymous access to Nexus count as one user, or as many users that may be accessing Nexus anonymously?
A. If you are exposing your Nexus instances publicly (outside your organization), then the anonymous access counts as one user. If the anonymous access is within your organization, then each individual user as defined by the license agreement applies, despite the access not requiring a login.
Q. How can I verify if I am in compliance with the number of licensed users?
A. As an Administrator user, you can access the Administration -> Licensing tab in Nexus, then click the "Active Users Report" button. You will then have access to a report of all the unique IP addresses accessing nexus within the last 7 days. This information is intended as an approximation tool only. In many situations ( eg. reverse proxy fronting Nexus ), the number of unique IPs accessing Nexus will be skewed.
Other approaches to determining the number of users who can access Nexus involve counting the user accounts in the sonatype-work/nexus/conf/security.xml file or having your LDAP administrators report on the number of users in the groups which have been given access to Nexus.
If you have any questions or concerns about Nexus Professional licensing please contact us at email@example.com