coredns/man/coredns-view.7

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.TH "COREDNS-VIEW" 7 "June 2025" "CoreDNS" "CoreDNS Plugins"

.SH "NAME"
.PP
\fIview\fP - defines conditions that must be met for a DNS request to be routed to the server block.

.SH "DESCRIPTION"
.PP
\fIview\fP defines an expression that must evaluate to true for a DNS request to be routed to the server block.
This enables advanced server block routing functions such as split dns.

.SH "SYNTAX"
.PP
.RS

.nf
view NAME {
  expr EXPRESSION
}

.fi
.RE

.IP \(bu 4
\fB\fCview\fR \fBNAME\fP - The name of the view used by metrics and exported as metadata for requests that match the
view's expression
.IP \(bu 4
\fB\fCexpr\fR \fBEXPRESSION\fP - CoreDNS will only route incoming queries to the enclosing server block
if the \fBEXPRESSION\fP evaluates to true. See the \fBExpressions\fP section for available variables and functions.
If multiple instances of view are defined, all \fBEXPRESSION\fP must evaluate to true for CoreDNS will only route
incoming queries to the enclosing server block.


.PP
For expression syntax and examples, see the Expressions and Examples sections.

.SH "EXAMPLES"
.PP
Implement CIDR based split DNS routing.  This will return a different
answer for \fB\fCtest.\fR depending on client's IP address.  It returns ...
* \fB\fCtest. 3600 IN A 1.1.1.1\fR, for queries with a source address in 127.0.0.0/24
* \fB\fCtest. 3600 IN A 2.2.2.2\fR, for queries with a source address in 192.168.0.0/16
* \fB\fCtest. 3600 IN AAAA 2001:0DB8::1\fR, for queries with a source address in 2001:0DB8::/32
* \fB\fCtest. 3600 IN A 3.3.3.3\fR, for all others

.PP
.RS

.nf
\&. {
  view example1 {
    expr incidr(client\_ip(), '127.0.0.0/24')
  }
  hosts {
    1.1.1.1 test
  }
}

\&. {
  view example2 {
    expr incidr(client\_ip(), '192.168.0.0/16')
  }
  hosts {
    2.2.2.2 test
  }
}

\&. {
  view v6\_example1 {
    expr incidr(client\_ip(), '2001:0DB8::/32')
  }
  hosts {
    2001:0DB8::1 test
  }
}

}

\&. {
  hosts {
    3.3.3.3 test
  }
}

.fi
.RE

.PP
Send all \fB\fCA\fR and \fB\fCAAAA\fR requests to \fB\fC10.0.0.6\fR, and all other requests to \fB\fC10.0.0.1\fR.

.PP
.RS

.nf
\&. {
  view example {
    expr type() in ['A', 'AAAA']
  }
  forward . 10.0.0.6
}

\&. {
  forward . 10.0.0.1
}

.fi
.RE

.PP
Send all requests for \fB\fCabc.*.example.com\fR (where * can be any number of labels), to \fB\fC10.0.0.2\fR, and all other
requests to \fB\fC10.0.0.1\fR.
Note that the regex pattern is enclosed in single quotes, and backslashes are escaped with backslashes.

.PP
.RS

.nf
\&. {
  view example {
    expr name() matches '^abc\\\\..*\\\\.example\\\\.com\\\\.$'
  }
  forward . 10.0.0.2
}

\&. {
  forward . 10.0.0.1
}

.fi
.RE

.SH "EXPRESSIONS"
.PP
To evaluate expressions, \fIview\fP uses the expr-lang/expr package ( https://github.com/expr-lang/expr
\[la]https://github.com/expr-lang/expr\[ra] ).
For example, an expression could look like:
\fB\fC(type() == 'A' && name() == 'example.com.') || client_ip() == '1.2.3.4'\fR.

.PP
All expressions should be written to evaluate to a boolean value.

.PP
See https://github.com/expr-lang/expr/blob/master/docs/Language-Definition.md
\[la]https://github.com/expr-lang/expr/blob/master/docs/Language-Definition.md\[ra] as a detailed reference for valid syntax.

.SS "AVAILABLE EXPRESSION FUNCTIONS"
.PP
In the context of the \fIview\fP plugin, expressions can reference DNS query information by using utility
functions defined below.

.SS "DNS QUERY FUNCTIONS"
.IP \(bu 4
\fB\fCbufsize() int\fR: the EDNS0 buffer size advertised in the query
.IP \(bu 4
\fB\fCclass() string\fR: class of the request (IN, CH, ...)
.IP \(bu 4
\fB\fCclient_ip() string\fR: client's IP address, for IPv6 addresses these are enclosed in brackets: \fB\fC[::1]\fR
.IP \(bu 4
\fB\fCdo() bool\fR: the EDNS0 DO (DNSSEC OK) bit set in the query
.IP \(bu 4
\fB\fCid() int\fR: query ID
.IP \(bu 4
\fB\fCname() string\fR: name of the request (the domain name requested ending with a dot): \fB\fCexample.com.\fR
.IP \(bu 4
\fB\fCopcode() int\fR: query OPCODE
.IP \(bu 4
\fB\fCport() string\fR: client's port
.IP \(bu 4
\fB\fCproto() string\fR: protocol used (tcp or udp)
.IP \(bu 4
\fB\fCserver_ip() string\fR: server's IP address; for IPv6 addresses these are enclosed in brackets: \fB\fC[::1]\fR
.IP \(bu 4
\fB\fCserver_port() string\fR : server's port
.IP \(bu 4
\fB\fCsize() int\fR: request size in bytes
.IP \(bu 4
\fB\fCtype() string\fR: type of the request (A, AAAA, TXT, ...)


.SS "UTILITY FUNCTIONS"
.IP \(bu 4
\fB\fCincidr(ip string, cidr string) bool\fR: returns true if \fIip\fP is within \fIcidr\fP
.IP \(bu 4
\fB\fCmetadata(label string)\fR - returns the value for the metadata matching \fIlabel\fP


.SH "METADATA"
.PP
The view plugin will publish the following metadata, if the \fImetadata\fP
plugin is also enabled:

.IP \(bu 4
\fB\fCview/name\fR: the name of the view handling the current request