In total there are 3 different realm (server) types in DHD!
Heirs of the Dragon-REALMS
This is the most common version of the game.
You build up a city, feed your dragons, recruit generals and train troops. Each of the mentioned improves through levels. You can choose to defend your city in one of three way, either with your whole army, part of your army or not at all.
Just as it Sounds - one hardcore version of DoA. Your troops are always protecting your city. No possibility to set up a so called custom Wall. The good news is that only 50% of your troops die - but it not called hardcore without reason.
Age of Dragons-REALMS
This Is similar to Hardcore - as you are always defending your city. But here you get one explanation of the battle - and all troops involved will die. You get statistics over your progress. This is a funny challenging version of the Game
Each version has in common that you get rewards for daily login. You set up an army to fight in the arena, let your dragons meet other dragons in battle in a dragon battleground scenario!
Plus a lot more.