Twitter is ~7.5K employees.
Zendesk is ~6K employees.
Slack is ~2.5K employees.
Zillow (Realestate online marketplace) is ~8K employees.
Glassdoor probably over ~1K employees.
Facebook - ~60K employees (!!!)
Asana - ~1.6K employees
Okta - ~5K employees
Twitch - ~15K employees
Zoom - ~7K employees.
I am saying all of these because many professionals agree that there are not enough talented people in the software industry, and I agree with that saying, yet how it can be solved when the current software companies are so huge?
Twitter size in 2009 - 29 employees according to a google search.
Whatsapp when it was sold to FB? 55 employees. They were much smaller when they already support hundreds of millions of users.
All those companies still probably had large-scale issues back then, uptime concerns, and much more - and all of that with 10+ year old technology!