retry

retry

Name

Plugin Retry is able to selectively fanout the query to another upstream server, depending the error result provided by the initial resolver

Description

The retry plugin allows set of upstreams be specified which will be used if the plugin chain returns specific error messages. The retry plugin utilizes the fanout plugin (https://github.com/networkservicemesh/fanout) to sent fanout query the specified upstreams.

Syntax

{
    retry [original] RCODE_1[,RCODE_2,RCODE_3...] . DNS_RESOLVERS
}

• original is optional flag. If it is set then retry uses original request instead of potentially changed by other plugins
• RCODE is the string representation of the error response code. The complete list of valid rcode strings are defined as RcodeToString in https://github.com/miekg/dns/blob/master/msg.go, examples of which are SERVFAIL, NXDOMAIN and REFUSED. At least one rcode is required, but multiple rcodes may be specified, delimited by commas.
• DNS_RESOLVERS accepts dns resolvers list.

Building CoreDNS with Retry

When building CoreDNS with this plugin, retry should be positioned before forward in /plugin.cfg.

Examples

Retry to local DNS server

The following specifies that all requests are forwarded to 8.8.8.8. If the response is NXDOMAIN, retry will fanout the request to 192.168.1.1:53, and reply to client accordingly.

. {
	forward . 8.8.8.8
	retry NXDOMAIN . 192.168.1.1:53
	log
}

Retry with original request used

The following specify that original query will be forwarded to 192.168.1.1:53 if 8.8.8.8 response is NXDOMAIN. original means no changes from next plugins on request. With no original flag retry will forward request with EDNS0 option (set by rewrite).

. {
	forward . 8.8.8.8
	rewrite edns0 local set 0xffee 0x61626364
	retry original NXDOMAIN . 192.168.1.1:53
	log
}

Multiple retries

Multiple retries can be specified, as long as they serve unique error responses.

. {
    forward . 8.8.8.8
    retry NXDOMAIN . 192.168.1.1:53
    retry original SERVFAIL,REFUSED . 192.168.100.1:53
    log
}