Live polls during a webinar

Design live polls for a webinar platform. The host launches a multiple-choice question, attendees vote within 60 seconds, and everyone, attendees and host, sees a results bar chart that updates live. Each attendee gets one vote per poll and can change it until the poll closes. The platform runs about 2,000 webinars a day; most have under 300 attendees, and the largest have 20,000, all of whom may vote in the first 10 seconds. Attendees are already connected to the webinar over WebSocket for chat. Describe how votes are recorded, how counts are kept, and how results reach 20,000 screens without overwhelming the system.