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185 lines
4.5 KiB
Groff
185 lines
4.5 KiB
Groff
.\" Generated by Mmark Markdown Processer - mmark.miek.nl
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.TH "COREDNS-VIEW" 7 "September 2022" "CoreDNS" "CoreDNS Plugins"
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.SH "NAME"
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.PP
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\fIview\fP - defines conditions that must be met for a DNS request to be routed to the server block.
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.SH "DESCRIPTION"
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.PP
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\fIview\fP defines an expression that must evaluate to true for a DNS request to be routed to the server block.
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This enables advanced server block routing functions such as split dns.
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.SH "SYNTAX"
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.PP
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.RS
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.nf
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view NAME {
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expr EXPRESSION
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}
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.fi
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.RE
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.IP \(bu 4
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\fB\fCview\fR \fBNAME\fP - The name of the view used by metrics and exported as metadata for requests that match the
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view's expression
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.IP \(bu 4
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\fB\fCexpr\fR \fBEXPRESSION\fP - CoreDNS will only route incoming queries to the enclosing server block
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if the \fBEXPRESSION\fP evaluates to true. See the \fBExpressions\fP section for available variables and functions.
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If multiple instances of view are defined, all \fBEXPRESSION\fP must evaluate to true for CoreDNS will only route
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incoming queries to the enclosing server block.
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.PP
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For expression syntax and examples, see the Expressions and Examples sections.
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.SH "EXAMPLES"
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.PP
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Implement CIDR based split DNS routing. This will return a different
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answer for \fB\fCtest.\fR depending on client's IP address. It returns ...
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* \fB\fCtest. 3600 IN A 1.1.1.1\fR, for queries with a source address in 127.0.0.0/24
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* \fB\fCtest. 3600 IN A 2.2.2.2\fR, for queries with a source address in 192.168.0.0/16
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* \fB\fCtest. 3600 IN A 3.3.3.3\fR, for all others
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.PP
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.RS
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.nf
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\&. {
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view example1 {
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expr incidr(client\_ip(), '127.0.0.0/24')
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}
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hosts {
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1.1.1.1 test
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}
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}
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\&. {
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view example2 {
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expr incidr(client\_ip(), '192.168.0.0/16')
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}
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hosts {
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2.2.2.2 test
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}
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}
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\&. {
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hosts {
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3.3.3.3 test
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}
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}
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.fi
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.RE
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.PP
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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.
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.PP
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.RS
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.nf
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\&. {
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view example {
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expr type() in ['A', 'AAAA']
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}
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forward . 10.0.0.6
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}
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\&. {
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forward . 10.0.0.1
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}
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.fi
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.RE
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.PP
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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
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requests to \fB\fC10.0.0.1\fR.
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Note that the regex pattern is enclosed in single quotes, and backslashes are escaped with backslashes.
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.PP
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.RS
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.nf
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\&. {
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view example {
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expr name() matches '^abc\\\\..*\\\\.example\\\\.com\\\\.$'
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}
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forward . 10.0.0.2
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}
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\&. {
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forward . 10.0.0.1
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}
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.fi
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.RE
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.SH "EXPRESSIONS"
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.PP
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To evaluate expressions, \fIview\fP uses the antonmedv/expr package (https://github.com/antonmedv/expr
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\[la]https://github.com/antonmedv/expr\[ra]).
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For example, an expression could look like:
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\fB\fC(type() == 'A' && name() == 'example.com') || client_ip() == '1.2.3.4'\fR.
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.PP
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All expressions should be written to evaluate to a boolean value.
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.PP
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See https://github.com/antonmedv/expr/blob/master/docs/Language-Definition.md
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\[la]https://github.com/antonmedv/expr/blob/master/docs/Language-Definition.md\[ra] as a detailed reference for valid syntax.
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.SS "AVAILABLE EXPRESSION FUNCTIONS"
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.PP
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In the context of the \fIview\fP plugin, expressions can reference DNS query information by using utility
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functions defined below.
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.SS "DNS QUERY FUNCTIONS"
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.IP \(bu 4
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\fB\fCbufsize() int\fR: the EDNS0 buffer size advertised in the query
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.IP \(bu 4
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\fB\fCclass() string\fR: class of the request (IN, CH, ...)
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.IP \(bu 4
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\fB\fCclient_ip() string\fR: client's IP address, for IPv6 addresses these are enclosed in brackets: \fB\fC[::1]\fR
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.IP \(bu 4
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\fB\fCdo() bool\fR: the EDNS0 DO (DNSSEC OK) bit set in the query
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.IP \(bu 4
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\fB\fCid() int\fR: query ID
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.IP \(bu 4
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\fB\fCname() string\fR: name of the request (the domain name requested)
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.IP \(bu 4
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\fB\fCopcode() int\fR: query OPCODE
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.IP \(bu 4
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\fB\fCport() string\fR: client's port
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.IP \(bu 4
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\fB\fCproto() string\fR: protocol used (tcp or udp)
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.IP \(bu 4
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\fB\fCserver_ip() string\fR: server's IP address; for IPv6 addresses these are enclosed in brackets: \fB\fC[::1]\fR
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.IP \(bu 4
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\fB\fCserver_port() string\fR : client's port
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.IP \(bu 4
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\fB\fCsize() int\fR: request size in bytes
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.IP \(bu 4
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\fB\fCtype() string\fR: type of the request (A, AAAA, TXT, ...)
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.SS "UTILITY FUNCTIONS"
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.IP \(bu 4
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\fB\fCincidr(ip string, cidr string) bool\fR: returns true if \fIip\fP is within \fIcidr\fP
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.IP \(bu 4
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\fB\fCmetadata(label string)\fR - returns the value for the metadata matching \fIlabel\fP
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.SH "METADATA"
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.PP
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The view plugin will publish the following metadata, if the \fImetadata\fP
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plugin is also enabled:
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.IP \(bu 4
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\fB\fCview/name\fR: the name of the view handling the current request
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