The DNS server or "domain name server" is responsible for consulting and managing the database in real time to respond to requests that relate a server to a domain.
As a rule, the DNS server is hosted in dedicated service, and they refer to its use in the implementation of primary and secondary DNS server (s).
Primary, primary or master server: a DNS server is called that stores the DNS zone information of the domain in its own database.
Secondary or slave server: when the information of the primary server cannot be obtained or is inaccessible, this server becomes secondary or slave for this information. This situation occurs when a primary server cannot resolve a query request and uses the information available on another registered secondary DNS server.
The domain name system is designed so that each domain has at least 2 DNS server names. These types of systems are generally implemented to create a server cluster that stores identical DNS zone data in several places, thus creating redundancy and secondary server availability in case of failures in the primary server.