Nexus Routes are like filters you can apply to Nexus Groups, they allow you to configure Nexus to include or exclude repositories from a particular artifact search when Nexus is trying to locate an artifact in a repository group. There are a number of different scenarios in which you might configure a route in Nexus.
The most common is when you want to make sure that you are retrieving artifacts in a particular group ID from a particular repository. This is especially useful when you want to make sure that you are trying to retrieve your own organization’s artifacts from the hosted Release and Snapshot repositories.
Routes are applicable when you are trying to resolve an artifact from a repository group; using Routes allow you to modify the repositories Nexus will consult when it tries to resolve an artifact from a group of repositories.
Figure 6.22, “Routes Configuration Screen in Nexus” shows the Repository Route Configuration screen. Clicking on a route will bring up a screen which will allow you to configure the properties of a route. The configuration options available for a route are:
- URL Pattern
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This is the pattern which Nexus will use to match a request to Nexus. If the regular expression in this pattern is matched, Nexus will either include or exclude the listed repositories from a particular artifact query. In Figure 6.22, “Routes Configuration Screen in Nexus” the two patterns are:
- ".*/(com|org)/somecompany/.*"
- This pattern would match all paths which includes either "/com/somecompany/" or "/org/somecompany/". The expression in the parenthesis matches either com or org, and the ".*" matches zero or more characters. You would use a route like this to match your own organization’s artifacts and map these requests to the hosted Nexus Releases and Snapshots repositories.
- ".*/org/some-oss/.*"
- This pattern is used in an exclusive route. It matches every path that contains "/org/some-oss/". This particular exclusive route excludes the local hosted Releases and Snapshots directory for all artifacts which match this path. When Nexus tries to resolve artifacts that match this path, it will exclude the Releases and Snapshots repositories.
- Rule Type
- Rule Type can be either "inclusive" or "exclusive". An inclusive rule type defines the set of repositories which should be searched for artifacts when the URL pattern has been matched. An exclusive rule type defines repositories which should not be searched for a particular artifact.
- Ordered Route Repositories
- This is an ordered list of repositories which Nexus will search to locate a particular artifact. Nexus searches top to bottom; if it’s looking for an artifact, it will return the first match. When Nexus is looking for metadata, all repositories in a group are checked and the results are merged. The merging is applied giving preference to the earlier repositories. This is relevant when a project is looking for a LATEST or a RELEASE version. Within a Nexus Group, you should define the release repositories before the snapshot repositories, otherwise LATEST may incorrectly resolve to a snapshot version.
In this figure you can see the two dummy Routes that Nexus has as default routes.
The first route is an inclusive route, it is provided as an example of a custom route an organization might use to make sure that internally generated artifacts are resolved from the Releases and Snapshots repositories. If your organization’s group IDs all start with com.somecompany, and if you deploy internally generated artifacts to the Releases and Snapshots repositories, this Route will make sure that Nexus doesn’t waste time trying to resolve these artifacts from public Maven repositories like the Maven Central Repository or the Apache Snapshots repository.
The second dummy route is an exclusive route. This route excludes the Releases and Snapshots repositories when the request path contains "/org/some-oss". This example might make more sense if we replaced "some-oss" with "apache" or "codehaus". If the pattern was "/org/apache", this rule is telling Nexus to exclude the internal Releases and Snapshots repositories when it is trying to resolve these dependencies. In other words, don’t bother looking for an Apache dependency in your organization’s internal repositories.
What if there is a conflict between two routes? Nexus will process inclusive routes before it will process the exclusive routes. Remember that Nexus Routes only affect Nexus' resolution of artifacts when it is searching a Group. When Nexus starts to resolve an artifact from a Nexus Group it will start with the list of repositories in a group. If there are matching inclusive routes, Nexus will then take the intersection of the repositories in the Group and the repositories in the inclusive Nexus Route. The order as defined in the Nexus Group will not be affected by the Inclusive route. Nexus will then take the result of applying the inclusive route and apply the exclusive route to that list of repositories. The resulting list is then searched for a matching artifact.
One straightforward use of routes is to create a route that excludes the Maven Central repository from all searches for your own organization’s hosted artifacts. If you are deploying your own artifacts to Nexus under a groupId of org.mycompany, and if you are not deploying these artifacts to a public repository, you can create a rule that tells Nexus not to interrogate Central for your own organization’s artifacts. This will improve performance because Nexus will not need to communicate with a remote repository when it serves your own organization’s artifacts. In addition to the performance benefits, excluding Central from searches for your own artifacts will reduce needless queries to the public repositories.
To summarize, there are creative possibilities with Routes that the designers of Nexus may not have anticipated, but we advise you to proceed with caution if you start relying on conflicting or overlapping Routes. Use Routes sparingly, and use course URL patterns, as Nexus evolves there will be more features which allow for more fine grained rules to allow you to prohibit requests for specific artifacts and specific versions of artifacts. Remember that routes are only applied to Nexus Groups, routes are not used when an artifact is requested from a specific repository.
