We have an advanced DDoS protection system with more than a Terabit's capacity on the edges of our network, and this is included in all accounts free of charge.
Our machine learning DDoS system will detect an unusual traffic amount and type of activity hitting our network. Depending on the amount of traffic it will either flag it for manual intervention, or automatically send all traffic for the network range that includes the target IP address(es) to a filtering system. The filtering system has advanced scrubbing algorithms that send bad data to a black hole, while rerouting good data back to our network.
The portion of attacks that require manual intervention (suspect but not convinced it's malicious, or too small to be confidently considered an attack) are monitored 24/7 by our datacentre's UK Security Operations Centre.
If you host with us and are under DDoS attack, you may notice a minute or two's outage (while the system determines an attack is underway) and then your traffic should return to normal while the DDoS protection system does its work, leaving you protected and your instances still online.
After a 24 hour period, if the traffic is deemed to have returned to a normal level and consistency, the network will switch back to not going via the traffic scrubbing system. There may be a blip of up to 30 seconds when instances on the affected network section have their routing updated (this is the way BGP routing works). It will normally be much less than this (within a second for UK traffic).
Either way, your instances are protected from these dangerous attacks that can take other hosts offline.