What DNS does

DNS maps names to records, including the addresses used to reach a service. Resolver caches reduce repeated queries. A change to a DNS record may take time to reach every resolver because cached answers have a time to live.

Why latency varies

Round-trip time depends on the route, congestion and processing along the path. A nearby location is not always reached by a short route. Compare repeated measurements and distinguish network latency from application response time.

Checking a secure connection

TLS encrypts data in transit and verifies the identity of a service using its certificate. Keep systems current, check the name shown in the certificate, and investigate verification errors instead of disabling certificate checks.