cache

README

cache

cache enables a frontend cache.

Syntax

cache [ttl] [zones...]

• ttl max TTL in seconds. If not specified, the TTL of the reply (SOA minimum or minimum TTL in the answer section) will be used.
• 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. For the negative cache, the SOA's MinTTL value is used.

A cache mostly makes sense with a middleware that is potentially slow (e.g., a proxy that retrieves an answer), or to minimize backend queries for middleware like etcd. Using a cache with the file middleware essentially doubles the memory load with no conceivable increase of query speed.

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).

Documentation

Index

• type Cache
  • func NewCache(ttl int, zones []string, next middleware.Handler) Cache
  • func (c Cache) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (int, error)
• type ResponseWriter
  • func NewCachingResponseWriter(w dns.ResponseWriter, cache *gcache.Cache, cap time.Duration) *ResponseWriter
  • func (c *ResponseWriter) Hijack()
  • func (c *ResponseWriter) Write(buf []byte) (int, error)
  • func (c *ResponseWriter) WriteMsg(res *dns.Msg) error

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.

func NewCache

func NewCache(ttl int, zones []string, next middleware.Handler) Cache

NewCache returns a new cache.

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
	// contains filtered or unexported fields
}

ResponseWriter is a response writer that caches the reply message.

func NewCachingResponseWriter

func NewCachingResponseWriter(w dns.ResponseWriter, cache *gcache.Cache, cap time.Duration) *ResponseWriter

NewCachingResponseWriter returns a new ResponseWriter.

func (*ResponseWriter) Hijack

func (c *ResponseWriter) Hijack()

Hijack implements the dns.ResponseWriter interface.

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.