CoWIN is the government portal Indians used to register for a COVID-19 vaccine. On 28 April 2021 at 4 pm, registration opened for everyone aged 18 to 44. Everyone who wanted a slot knew the exact minute to show up.
The first minutes were rough. Users on social media said the CoWIN site and the Aarogya Setu app were not responding, and some said their one-time passwords never arrived. Aarogya Setu posted that there was "a minor glitch at 4 pm that was fixed".
The government's numbers tell the other side. According to its statement that evening, in the three hours from 4 pm to 7 pm CoWIN received 383 million API hits, peaking early at 2.7 million hits per minute. More than 80 lakh (8 million) people registered in those three hours, and 1.45 crore SMS messages went out. The statement said media reports of a server crash were "incorrect and are without any basis" and that the system was handling 55,000 hits per second and was "completely stable". By the end of the day, nearly 1.33 crore (13.3 million) people had registered. More than 35 lakh of them signed up in the first hour.
But registering was only step one. Most people who registered could not book a vaccination slot. Scroll reported that slots were showing mainly for people over 45, with some appointments only around July, because new vaccine supplies for younger adults were not expected until June or later.
- 383 million API hits from 4 pm to 7 pm
- Up to 2.7 million hits per minute at the start; 55,000 per second, per the government
- More than 80 lakh registrations in three hours; nearly 1.33 crore by the end of the day
- 1.45 crore SMS messages delivered
Why it matters: A system can survive a stampede and still disappoint everyone, because the real limit was outside the software. When everyone arrives at one announced minute, plan for the first few minutes and for what users can actually do once they're in.