Real-Time Collaborative Whiteboard

A company is building an online collaborative whiteboard where thousands of users can work on the same board at once. When one user moves an object, every other connected user must receive that change immediately. The platform needs persistent two-way connections, real-time updates, millions of connection events, automatic scaling, no server fleet to manage, and authentication before anyone joins a board. Board state has to be stored durably, while the collaboration state that is read and written constantly should be extremely fast.