After migrating from Nexus 2 to Nexus 3, you may notice that the default URL path to a repository is something like below:
http://localhost:8081/repository/sample
In Nexus 2, the default URL path to a repository is something like below:
http://localhost:8081/nexus/content/repositories/sample
This would mean that your builds would all need to change their URL paths to work.
It is possible for Nexus 3 to handle Nexus 2 type URL paths.
1) Ensure that Nexus 2 and Nexus 3 have the same context path. By default Nexus 2 has context path "/nexus" and Nexus 3 has blank context path by default. In Nexus 3, you can set context path in nexus.properties:
nexus-context-path=/nexus
Nexus 3 Application Context Path
2) Enable Capability called "NXRM2 style URLs"