fanout

Description

Each incoming DNS query that hits the CoreDNS fanout plugin will be replicated in parallel to each listed IP (i.e. the DNS servers). The first non-negative response from any of the queried DNS Servers will be forwarded as a response to the application’s DNS request.

Syntax

• tls CERT KEY CA define the TLS properties for TLS connection. From 0 to 3 arguments can be provided with the meaning as described below

  • tls - no client authentication is used, and the system CAs are used to verify the server certificate
  • tls CA - no client authentication is used, and the file CA is used to verify the server certificate
  • tls CERT KEY - client authentication is used with the specified cert/key pair. The server certificate is verified with the system CAs
  • tls CERT KEY CA - client authentication is used with the specified cert/key pair. The server certificate is verified using the specified CA file

• tls_servername NAME allows you to set a server name in the TLS configuration; for instance 9.9.9.9 needs this to be set to dns.quad9.net. Multiple upstreams are still allowed in this scenario, but they have to use the same tls_servername. E.g. mixing 9.9.9.9 (QuadDNS) with 1.1.1.1 (Cloudflare) will not work.

• worker-count is the number of parallel queries per request. By default equals to count of IP list. Use this only for reducing parallel queries per request.

• policy - specifies the policy of DNS server selection mechanism. The default is sequential.

  • sequential - select DNS servers one-by-one based on its order
  • weighted-random - select DNS servers randomly based on weighted-random-server-count and weighted-random-load-factor params.

• weighted-random-server-count is the number of DNS servers to be requested. Equals to the number of specified IPs by default. Used only with the weighted-random policy.

• weighted-random-load-factor - the probability of selecting a server. This is specified in the order of the list of IP addresses and takes values between 1 and 100. By default, all servers have an equal probability of 100. Used only with the weighted-random policy.

• network is a specific network protocol. Could be tcp, udp, tcp-tls.

• except is a list is a space-separated list of domains to exclude from proxying.

• except-file is the path to file with line-separated list of domains to exclude from proxying.

• attempt-count is the number of attempts to connect to upstream servers that are needed before considering an upstream to be down. If 0, the upstream will never be marked as down and request will be finished by timeout. Default is 3.

• timeout is the timeout of request. After this period, attempts to receive a response from the upstream servers will be stopped. Default is 30s.

• race gives priority to the first result, whether it is negative or not, as long as it is a standard DNS result.

Metrics

If monitoring is enabled (via the prometheus plugin) then the following metric are exported:

• coredns_fanout_request_duration_seconds{to} - duration per upstream interaction.
• coredns_fanout_request_count_total{to} - query count per upstream.
• coredns_fanout_response_rcode_count_total{to, rcode} - count of RCODEs per upstream.

Where to is one of the upstream servers (TO from the config), rcode is the returned RCODE from the upstream.

Examples

Proxy all requests within example.org. to a nameservers running on a different ports. The first positive response from a proxy will be provided as the result.

example.org {
    fanout . 127.0.0.1:9005 127.0.0.1:9006 127.0.0.1:9007 127.0.0.1:9008
}

Sends parallel requests between three resolvers, one of which has a IPv6 address via TCP. The first response from proxy will be provided as the result.

. {
    fanout . 10.0.0.10:53 10.0.0.11:1053 [2003::1]:53 {
        network TCP
    }
}

Proxying everything except requests to example.org

. {
    fanout . 10.0.0.10:1234 {
        except example.org
    }
}

Proxy everything except example.org using the host’s resolv.conf’s nameservers:

. {
    fanout . /etc/resolv.conf {
        except example.org
    }
}

Proxy all requests to 9.9.9.9 using the DNS-over-TLS protocol. Note the tls-server is mandatory if you want a working setup, as 9.9.9.9 can’t be used in the TLS negotiation.

. {
    fanout . tls://9.9.9.9 {
       tls-server dns.quad9.net
    }
}

Sends parallel requests between five resolvers via UDP uses two workers and without attempting to reconnect. The first positive response from a proxy will be provided as the result.

. {
    fanout . 10.0.0.10:53 10.0.0.11:53 10.0.0.12:53 10.0.0.13:1053 10.0.0.14:1053 {
        worker-count 2
    }
}

Multiple upstream servers are configured but one of them is down, query a non-existent domain. If race is enable, we will get NXDOMAIN result quickly, otherwise we will get "connection timed out" result in a few seconds.

. {
    fanout . 10.0.0.10:53 10.0.0.11:53 10.0.0.12:53 10.0.0.13:1053 10.0.0.14:1053 {
        race
    }
}

Sends parallel requests between two randomly selected resolvers. Note, that 127.0.0.1:9007 would be selected more frequently as it has the highest weighted-random-load-factor.

example.org {
    fanout . 127.0.0.1:9005 127.0.0.1:9006 127.0.0.1:9007 {
      policy weighted-random
      weighted-random-server-count 2
      weighted-random-load-factor 50 70 100
    }
}

Sends parallel requests between three resolver sequentially (default mode).

example.org {
    fanout . 127.0.0.1:9005 127.0.0.1:9006 127.0.0.1:9007 {
        policy sequential
    }
}

Also See

See the fanout.