I'm diving into the best practices for DNS TTL values, especially for highly available services using Azure Firewall as a DNS Proxy. The default TTL is set to 1 hour, but that seems too long for effective failover. What consequences should I be aware of if I decide to reduce the TTL for certain records? Additionally, how can I monitor potential cost increases associated with this? What strategies have you all implemented in your environments? Thanks for your help!
3 Answers
Using Azure Firewall with DNS Proxy doesn't add extra costs for DNS lookups, which is great! However, if you're running private DNS zones, there will be some associated costs, but they are relatively low. We switched to Azure Firewall from our previous Private DNS resolver, and it's been smooth overall.
Lowering the TTL can definitely help with failover times, but be prepared for more frequent lookups hitting your DNS servers, which could show up in your logs as a slight cost increase. In most cases I've seen, teams set critical records to a few minutes instead of the default hour, achieving a good balance. Keep an eye on query volumes for a week after making changes — that will give you insights into the impact! What’s your expected frequency of record changes?
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