Which two roles are available to a user invited to administer specific sites in read-only mode?

The role of Observer is specifically designed for users who need read-only access to the system. This role permits users to view the configuration and monitoring data of specific sites without the capability to make any changes. By having this limited access, Observers can effectively monitor the status and performance of the network while ensuring that no accidental modifications are made that could disrupt the system.

The other roles mentioned provide different levels of access and capabilities. For example, the Helpdesk role is typically intended for support staff who may need to perform troubleshooting and assist users, which implies a higher degree of access than just viewing information. The Administrator role carries permissions that allow the user to configure devices and manage the network, significantly surpassing the read-only constraint. Lastly, the Super user role generally encompasses all permissions and capabilities within the system, allowing for full control over all settings and data.

Therefore, the Observer role precisely aligns with the requirement for read-only access, making it the correct choice among the available options.