What are the most effective DNS caching strategies for cloud-based apps?

1 Why DNS caching matters

DNS caching can reduce the latency and bandwidth consumption of your cloud-based apps, as well as protect them from DNS failures or attacks. By storing the IP addresses of frequently accessed domains in a local or distributed cache, you can avoid unnecessary queries to the authoritative DNS servers, which may be slow, overloaded, or compromised. DNS caching can also help you handle dynamic changes in your cloud infrastructure, such as scaling up or down, migrating to different regions, or switching providers.

2 How DNS caching works

DNS caching can be implemented at different levels of the network stack, such as the operating system, the browser, the app, or the proxy. Each level has its own cache size, expiration time, and update mechanism. When a DNS query is made, the cache is checked first for a matching entry. If the entry is found and valid, the IP address is returned immediately. If the entry is missing or expired, the query is forwarded to the next level or the upstream DNS server.

3 What are the challenges of DNS caching

DNS caching is not without its drawbacks. One of the main challenges is cache consistency, which means ensuring that the cached entries reflect the current state of the domain name system. If a domain changes its IP address, the cache may become stale and return incorrect or outdated information. This can cause errors, delays, or security risks for your cloud-based apps. To prevent this, you need to use appropriate cache expiration and invalidation policies, as well as monitor and verify the cache content.

4 What are the best practices for DNS caching

When considering DNS caching for your cloud-based app, there is no single solution that fits all requirements and environments. However, some best practices are using a hierarchical and distributed caching architecture, setting short TTLs for dynamic or critical domains and longer TTLs for static or less important domains, employing cache invalidation techniques to inform caches of any changes in the domain name system, and implementing cache verification methods to prevent cache poisoning attacks. A hierarchical and distributed caching architecture can have multiple layers of caches with different scopes and granularities, such as a local cache on an app server, a regional cache on a cloud provider, and a global cache on a third-party service. Short TTLs can help avoid stale cache entries but increase the frequency of cache updates and queries, while longer TTLs reduce network traffic and latency but increase the risk of inconsistency. Cache invalidation techniques like DNS NOTIFY or DNS PUSH can update the cache entries faster and more accurately without relying on TTLs alone; however, they require coordination between the cache servers and authoritative servers. Verification methods like DNSSEC or DNSCurve can prevent cache poisoning attacks but require more computational and network resources as well as support from the cache servers and authoritative servers.

5 What are the tools for DNS caching

There are many tools and services available to help you implement and manage DNS caching for your cloud-based apps. BIND, Unbound, and dnsmasq are all free and open-source software that can act as a DNS server, resolver, or cache. They support various DNS features and standards such as DNSSEC and DNSCurve. Cloudflare is a commercial service offering a global network of DNS caches, along with additional features like DNSSEC, DNS PUSH, and DNS over HTTPS (DoH). Google Public DNS is another commercial service that provides a global network of DNS resolvers with features such as DNSSEC and DoH. All of these tools and services can be useful for managing DNS caching in the cloud.

6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?