Is there a way (or some plugin/add-on) to add servers to an environment in TFS Release Management 2015?
I came from a team that used Octopus Deploy for DevOps. One thing that was extremely helpful was the ability to add multiple servers to an environment. Then, when you execute deployment steps on an environment, it applies those actions to all the servers that are part of the environment -- making deployments super easy. I have yet to find similar functionality in TFS Release Management and it's quite sad. They have a concept of an environment, but it's more like a "stage" than a logical/physical group of servers. To deploy the same step to multiple servers in an environment, you have to re-create the step multiple times or specifically write the names of all the servers in each step. Sad!
There isn’t the feature that execute deployment steps on an environment and applies to all the servers that in the environment.
But for web-based release management, you can provide a comma separated list of machine IP addresses or FQDNs along with ports for many steps/tasks of remote deploy, such as PowerShell on Target Machines, IIS Web Deployment and so on.
There is an article that may benefit you: Environments in Release Management
Regarding server and client based release management, there is environment that can include multiple servers, but you need to add steps multiple times for each server. I recommend that you use web-based release management.