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# cache
*cache* enables a frontend cache. It will cache all records except zone transfers and metadata records.
## Syntax
~~~ txt
cache [TTL] [ZONES...]
~~~
* **TTL** max TTL in seconds. If not specified, the maximum TTL will be used which is 3600 for
noerror responses and 1800 for denial of existence ones.
Setting a TTL of 300 *cache 300* would cache the record up to 300 seconds.
* **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. A TTL of zero is not allowed.
If you want more control:
~~~ txt
cache [TTL] [ZONES...] {
success CAPACITY [TTL]
denial CAPACITY [TTL]
prefetch AMOUNT [[DURATION] [PERCENTAGE%]]
}
~~~
* **TTL** and **ZONES** as above.
* `success`, override the settings for caching successful responses, **CAPACITY** indicates the maximum
number of packets we cache before we start evicting (*randomly*). **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.
* `prefetch`, will prefetch popular items when they are about to be expunged from the cache.
Popular means **AMOUNT** queries have been seen no gaps of **DURATION** or more between them.
**DURATION** defaults to 1m. Prefetching will happen when the TTL drops below **PERCENTAGE**,
which defaults to `10%`. Values should be in the range `[10%, 90%]`. Note the percent sign is
mandatory. **PERCENTAGE** is treated as an `int`.
The minimum TTL allowed on resource records is 5 seconds.
## Metrics
If monitoring is enabled (via the *prometheus* directive) then the following metrics are exported:
* coredns_cache_size{type} - Total elements in the cache by cache type.
* coredns_cache_capacity{type} - Total capacity of the cache by cache type.
* coredns_cache_hits_total{type} - Counter of cache hits by cache type.
* coredns_cache_misses_total - Counter of cache misses.
Cache types are either "denial" or "success".
## Examples
Enable caching for all zones, but cap everything to a TTL of 10 seconds:
~~~
cache 10
~~~
Proxy to Google Public DNS and only cache responses for example.org (or below).
~~~
proxy . 8.8.8.8:53
cache example.org
~~~
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