Explanation
DNS (Domain Name System) is a service that translates human-friendly domain names into IP addresses that can be used to communicate over the Internet1. However, DNS queries and responses are usually sent in plain text, which means that anyone who can intercept the network traffic can see the domain names that the users are requesting. This poses a threat to the confidentiality and privacy of the users and their online activities2.
To ensure confidentiality between the DNS server and an upstream DNS provider, a technician should configure DOH (DNS over HTTPS). DOH is a protocol that encrypts DNS queries and responses using HTTPS (Hypertext Transfer Protocol Secure), which is a secure version of HTTP that uses SSL/TLS (Secure Sockets Layer/Transport Layer Security) to protect the data in transit3. By using DOH, the technician can prevent eavesdropping, tampering, or spoofing of DNS traffic by malicious actors3.
The other options are not the best steps to ensure confidentiality between the DNS server and an upstream DNS provider:
Option A: Enable DNSSEC (DNS Security Extensions). DNSSEC is a set of extensions that add digital signatures to DNS records, which can be used to verify the authenticity and integrity of the DNS data.
DNSSEC can prevent DNS cache poisoning attacks, where an attacker inserts false DNS records into a DNS server's cache, redirecting users to malicious websites. However, DNSSEC does not encrypt or hide the DNS queries and responses, so it does not provide confidentiality for DNS traffic2.
Option B: Implement single sign-on (SSO). SSO is a mechanism that allows users to access multiple services or applications with one set of credentials, such as a username and password. SSO can simplify the authentication process and reduce the risk of password compromise or phishing attacks. However, SSO does not affect the communication between the DNS server and an upstream DNS provider, so it does not provide confidentiality for DNS traffic.
Option D: Set up DNS over SSL (DNS over Secure Sockets Layer). This option is not a valid protocol for securing DNS traffic. SSL is a deprecated protocol that has been replaced by TLS (Transport Layer Security), which is more secure and robust. The correct protocol for encrypting DNS traffic using SSL/TLS is DOH (DNS over HTTPS), as explained above.

IaaS (Infrastructure as a Service) is a cloud service model that provides basic computing resources such as servers, storage, network, etc., to the customers. The customers have full control and flexibility over these resources and can install and configure any software they need on them. IaaS is suitable for applications that have a unique stack of dependencies that may not be supported by other cloud service models.