CoWIN took 383 million hits. Most people still couldn't book.

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383 million API hits in three hours. Most people still couldn't book. By the government's account, the servers held up. So what failed?

28 April 2021. Vaccine sign-ups open for everyone aged 18 to 44. Everyone knows the exact minute. Users say the site stops responding. Some say their OTPs never arrive. Then three hours of stampede. That evening, the government calls the crash reports incorrect.

The peak came right at the start. 2 point 7 million hits a minute. It was handling 55,000 hits a second, the statement said. And 1 point 4 5 crore SMS messages went out.

Sign-ups? Over 35 lakh in the first hour alone. Over 80 lakh in three hours. That's 8 million people. Nearly 1 point 3 3 crore by the end of the day.

But here's the catch. Registering was only step one. Next, you book a vaccination slot. Most people couldn't.

The software? By its own numbers, it held. Slots were showing mainly for people over 45. Some appointments only around July. New vaccine supply for younger adults? June or later.

The real queue wasn't at the servers. It was at the vaccines. You can survive a stampede and still disappoint everyone. So plan for what users can actually do once they're in.

Full breakdown in the lecture.