return an error for multiple use of some plugins (#1559 )

* plugins: Return error for multiple use of some

Return plugin.ErrOnce when a plugin that doesn't support it, is called
mutliple times.

This now adds it for: cache, dnssec, errors, forward, hosts, nsid.
And changes it slightly in kubernetes, pprof, reload, root.

* more tests

2018-02-28 18:16:05 -08:00

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dnssec

Name

dnssec - enable on-the-fly DNSSEC signing of served data.

Description

With dnssec any reply that doesn't (or can't) do DNSSEC will get signed on the fly. Authenticated denial of existence is implemented with NSEC black lies. Using ECDSA as an algorithm is preferred as this leads to smaller signatures (compared to RSA). NSEC3 is not supported.

This plugin can only be used once per Server Block.

Syntax

dnssec [ZONES... ] {
    key file KEY...
    cache_capacity CAPACITY
}

The specified key is used for all signing operations. The DNSSEC signing will treat this key as a CSK (common signing key), forgoing the ZSK/KSK split. All signing operations are done online. Authenticated denial of existence is implemented with NSEC black lies. Using ECDSA as an algorithm is preferred as this leads to smaller signatures (compared to RSA). NSEC3 is not supported.

If multiple dnssec plugins are specified in the same zone, the last one specified will be used (See bugs).

ZONES zones that should be signed. If empty, the zones from the configuration block are used.
key file indicates that KEY file(s) should be read from disk. When multiple keys are specified, RRsets will be signed with all keys. Generating a key can be done with dnssec-keygen: dnssec-keygen -a ECDSAP256SHA256 <zonename>. A key created for zone A can be safely used for zone B. The name of the key file can be specified in one of the following formats
- basename of the generated key Kexample.org+013+45330
- generated public key Kexample.org+013+45330.key
- generated private key Kexample.org+013+45330.private
cache_capacity indicates the capacity of the cache. The dnssec plugin uses a cache to store RRSIGs. The default for CAPACITY is 10000.

Metrics

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

coredns_dnssec_cache_size{type} - total elements in the cache, type is "signature".
coredns_dnssec_cache_capacity{type} - total capacity of the cache, type is "signature".
coredns_dnssec_cache_hits_total{} - Counter of cache hits.
coredns_dnssec_cache_misses_total{} - Counter of cache misses.

Examples

Sign responses for example.org with the key "Kexample.org.+013+45330.key".

example.org {
    dnssec {
        key file Kexample.org.+013+45330
    }
    whoami
}

Sign responses for a kubernetes zone with the key "Kcluster.local+013+45129.key".

cluster.local {
    kubernetes
    dnssec {
      key file Kcluster.local+013+45129
    }
}

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