A DNS cache stores recently resolved domain name queries to reduce latency and server load. Key design considerations include:
- Data Structure: A hash map is suitable for fast lookups (domain name to IP address). Each entry should include the IP address, TTL (Time To Live), and timestamp.
- Eviction Policy: When the cache is full, an eviction policy is needed. Least Frequently Used (LFU) is a good choice, prioritizing keeping frequently accessed records. Other options include LRU (Least Recently Used) or TTL-based expiration.
- Write Strategy: 'Write Around' is often used. New entries are written directly to the cache. If the cache is full, eviction occurs. Reads check the cache first; if a miss occurs, the query goes to the DNS server, and the result is added to the cache.
- Concurrency: Use thread-safe data structures or locking mechanisms to handle concurrent read and write operations.
- TTL Handling: Records must be automatically removed or marked as expired once their TTL is reached.
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