According to my monitoring it’s not the first or second downtime for GLDDNS 
It could be beneficial to have some sort of redundancy.
While there are two nameservers listed for GLDDNS.COM domain, they point to the same IP address.
So any time that single IP (and servers(s) behind it) is/are down or overloaded dynamic DNS stops working
Even if there is a load balancer and multiple DNS instances behind it’s still a single location/AWS region. I’d recommend spinning up another instance/load balancer elsewhere.
I understand this is free service for GL-INET router customers, and it’s one which improves the value of proposition; but not when it’s repeatedly down.
p.s. I do not want sound bitter and i really do appreciate GL-INET products.
Thank you!
If there is a serious ongoing DDOS issue it may make sense to consider a specialist offering for this service, such as Cloudflare or other DNS vendor which can absorb DDOS using multiple locations and anycast etc.