lightbulbBook reference: Xu, System Design Interview. Original notes kept below; rewrite them in your own words.
2.2.1 DNS
Resolvers cache A/AAAA records. Low TTL means faster failover and more lookup load.
Why it matters
A bad TTL or a deleted record takes the site down with a “healthy” cluster.
How it is used
Health-checked failover records. Do not rely on 30s TTL for instant DR — clients cache longer. Monitor resolution errors. Pin critical internal names in the mesh.