coredns/middleware/cache

cache

cache enables a frontend cache.

Syntax

cache [ttl] [zones...]

• ttl max TTL in seconds. If not specified, the maximum TTL will be used which is 1 hour for noerror responses and half an hour for denial of existence ones.
• zones zones it should cache for. If empty, the zones from the configuration block are used.

Each element in the cache is cached according to its TTL (with ttl as the max). For the negative cache, the SOA's MinTTL value is used. A cache can contain up to 10,000 items by default.

Or if you want more control:

cache [ttl] [zones...] {
    success capacity [ttl]
    denial capacity [ttl]
}

• ttl and zones as above.
• success, override the settings for caching noerror responses, capacity indicates the maximum number of packets we cache before we start evicting (LRU). Ttl overrides the cache maximum TTL.
• denial, override the settings for caching denial of existence responses, capacity indicates the maximum number of packets we cache before we start evicting (LRU). Ttl overrides the cache maximum TTL.

There is a third category (error) but those responses are never cached.

The minimum TTL allowed on resource records is 5 seconds.

If monitoring is enabled (via the prometheus directive) then the following extra metrics are added:

• coredns_cache_hit_count_total, and
• coredns_cache_miss_count_total

They both work on a per-zone basis and just count the hit and miss counts for each query.

Examples

cache 10

Enable caching for all zones, but cap everything to a TTL of 10 seconds.

proxy . 8.8.8.8:53
cache example.org

Proxy to Google Public DNS and only cache responses for example.org (or below).