How Protect my DNS Server in Cloud?

Hi
I have a DNS Server in my VPS in Cloud for my clients using my applicattion, am using unbound to make my dns server.
Am thinking in terms of security of my clients and my cloud server, i need to protect them.
How can i setup security in this server, my clients don’t have dedicated ip addresses, 99% have a dinamic ip address.
I need to protect the server from attacks, some ideas?

Thanks

@dmr
Most attacks on servers such as DNS servers that are on the web are Distributed Denial Of Services(DDoS)
there for this has to be the first attack you should protect your clients against.

You can follow the guides in the links below to get more ideas:

https://www.nsa.gov/ia/_.../i733-004r-2010.pdf


https://www.globo.tech/blog/protecting-your-dns-server-against-ddos-attacks/

@aaronkili45 thanks.
But some questions!
There’s no real way to fully protect yourself against a DDos attack as your server needs to respond to certain query.
But my server, need to answer response to external of my clients.
Limiting rate limit the queries i can resolv this problem?