Zerodha. They are the biggest stock broker in India with a team of less than 40 people. Check out their tech blog for their tech philosophy: https://zerodha.tech/blog/hello-world/
The zerodha post is ... hard to believe. Self managed _everything_ and one devops engineer, no SREs? Who's managing the self-hosted PostgreSQL instances with the hundreds of billions or rows of _financial_ data?