The first important question is, why does one need auto-scaling? Because one needs more video rooms simultaneously which is beyond the capabilities of a single media server.
WebRTC can be scaled in 2 different ways. One of the option is manual scaling i.e. when the need for new media server i.e. the load is predictable, it is possible to create new media servers manually but when the load is unpredictable and random, then manual scaling is not possible. Here an automated scaling is needed with the help of a load-balancer which will programmatically create / delete new media server based on the real time load.
Visit this link to know more how you can auto-scale your WebRTC infrastructure.