redisc

Name

redisc - enables a networked cache using Redis.

Description

With redisc responses can be cached for up to 3600s. Caching in Redis is mostly useful in a setup where multiple CoreDNS instances share a VIP. E.g. multiple CoreDNS pods in a Kubernetes cluster.

If Redis is not reachable this plugin will be a noop. The cache and redisc plugin can be used together, where cache is the L1 and redisc is the L2 level cache. If multiple CoreDNS instances get a cache miss for the same item, they will all be fetching the same information from an upstream and updating the cache, i.e. there is no (extra) coordination between those instances.

If Redis is not available CoreDNS will simply not cache anything if metrics are enabled this will be visible in the set_errors_total metric.

Syntax

redisc [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: redisc 300 would cache records up to 300 seconds.
• ZONES zones it should cache for. If empty, the zones from the configuration block are used.

Each element in the Redis cache is cached according to its TTL (with TTL as the max). For the negative cache, the SOA's MinTTL value is used. When no endpoint is specified the default of 127.0.0.1:6379 will be used.

If you want more control:

redisc [TTL] [ZONES...] {
    endpoint ENDPOINT
}

• TTL and ZONES as above.
• endpoint specifies which ENDPOINT to use for Redis, this default to 127.0.0.1:6379.

Metrics

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

• coredns_redisc_hits_total{server} - Counter of cache hits.
• coredns_redisc_misses_total{server} - Counter of cache misses.
• coredns_redisc_set_errors_total{server} - Counter of errors when connecting to Redis.
• coredns_redisc_drops_total{server} - Counter of dropped messages.

The server label indicates which server handled the request, see the metrics plugin for details.

Examples

Enable caching for all zones, cache locally and also cache for up to 40s in the cluster wide Redis.

. {
    cache 30
    redisc 40 {
        endpoint 10.0.240.1:69
    }
    whoami
}

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

. {
    proxy . 8.8.8.8:53
    redisc example.org
}

See Also

See the Redis site for more information on Redis. An external plugin called redis already exists, hence this is named redisc, for "redis cache".

Bugs

There is little unit testing.