Just to clarify, DigitalOcean does not offer any form of DoS mitigation services so they blackhole during a DoS. Its for 3 hours, a lot less than other providers.
If you've got a DoS issue, you definitely need a 3rd party DoS protection service. Cloudflare free works pretty well
It's not "a lot less than other providers". You know what happens when someone starts DDOSing one of my AWS servers? I get a CloudWatch alert saying "high inbound traffic" and that's it. They don't black hole the thing and cut off all traffic. Then, I can log in, see what's happening, and take my time diagnosing the problem. Even under a fairly heavy DDOS I never feared losing access. With DO, the black hole happens before the email alert. It's a terrible policy and I can't use or recommend DO until it's changed. I can't stick CloudFlare in front of every server I own.
If you've got a DoS issue, you definitely need a 3rd party DoS protection service. Cloudflare free works pretty well