Our business operates in a market that has a lot of wannabe hacker types: bored teenagers in the gaming community with the minimum knowledge required to order a DDOS. As such, we're very very careful about <i>never</i> leaking our IPs anywhere. This has been tricky at times but it's well worth it. Cloudflare has made our lives a lot easier as it handles the bulk of the requests. Still, a lot of what it takes to be DDOS resilient is just being able to scale to high concurrency very quickly: ability to cache everything at every level, read-only mode, CDN for everything including HTML when possible, API gateways and self imposed rate limiting to third party services. With that said, there's not much you can do if your IP leaks. Some often overlooked areas for IP leaks: user generated content (your server makes a request to a URL specified by the user), or even sending an email (even many services provide the origin sender IP - such as SendGrid - as a matter of policy, so we don't use those services.)<p>Still to do: developing our own online ML based monitor which can detect abnormal user behaviour before it becomes a problem (ie. aggressive HTML scrapers, burp suite scans, etc.)