cache

README

cache

cache enables a frontend cache. It will cache all records except zone transfers and metadata records.

Syntax

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. A set TTL of 300 cache 300 would cache the record up to 300 seconds. Smaller record provided TTLs will take precedence.
• 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. No cache invalidation triggered by other middlewares is available. Therefore even reloaded items might still be cached for the duration of the TTL.

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 successful 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.

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

Documentation

Overview

Package cache implements a cache.

Index

• Constants
• type Cache
  • func (c *Cache) Name() string
  • func (c *Cache) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (int, error)
• type ResponseWriter
  • func (c *ResponseWriter) Write(buf []byte) (int, error)
  • func (c *ResponseWriter) WriteMsg(res *dns.Msg) error

Constants

const (

	// Success is the class for caching positive caching.
	Success = "success"
	// Denial is the class defined for negative caching.
	Denial = "denial"
)

Types

type Cache

type Cache struct {
	Next  middleware.Handler
	Zones []string
	// contains filtered or unexported fields
}

Cache is middleware that looks up responses in a cache and caches replies. It has a success and a denial of existence cache.

func (*Cache) Name

func (c *Cache) Name() string

Name implements the Handler interface.

func (*Cache) ServeDNS

func (c *Cache) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (int, error)

ServeDNS implements the middleware.Handler interface.

type ResponseWriter

type ResponseWriter struct {
	dns.ResponseWriter
	*Cache
}

ResponseWriter is a response writer that caches the reply message.

func (*ResponseWriter) Write

func (c *ResponseWriter) Write(buf []byte) (int, error)

Write implements the dns.ResponseWriter interface.

func (*ResponseWriter) WriteMsg

func (c *ResponseWriter) WriteMsg(res *dns.Msg) error

WriteMsg implements the dns.ResponseWriter interface.