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Signed-off-by: Ondřej Benkovský <ondrej.benkovsky@jamf.com> Signed-off-by: Ondřej Benkovský <ondrej.benkovsky@jamf.com>
136 lines
3.8 KiB
Markdown
136 lines
3.8 KiB
Markdown
# view
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## Name
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*view* - defines conditions that must be met for a DNS request to be routed to the server block.
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## Description
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*view* 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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## Syntax
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```
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view NAME {
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expr EXPRESSION
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}
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```
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* `view` **NAME** - 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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* `expr` **EXPRESSION** - CoreDNS will only route incoming queries to the enclosing server block
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if the **EXPRESSION** evaluates to true. See the **Expressions** section for available variables and functions.
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If multiple instances of view are defined, all **EXPRESSION** must evaluate to true for CoreDNS will only route
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incoming queries to the enclosing server block.
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For expression syntax and examples, see the Expressions and Examples sections.
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## Examples
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Implement CIDR based split DNS routing. This will return a different
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answer for `test.` depending on client's IP address. It returns ...
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* `test. 3600 IN A 1.1.1.1`, for queries with a source address in 127.0.0.0/24
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* `test. 3600 IN A 2.2.2.2`, for queries with a source address in 192.168.0.0/16
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* `test. 3600 IN A 3.3.3.3`, for all others
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```
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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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```
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Send all `A` and `AAAA` requests to `10.0.0.6`, and all other requests to `10.0.0.1`.
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```
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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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```
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Send all requests for `abc.*.example.com` (where * can be any number of labels), to `10.0.0.2`, and all other
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requests to `10.0.0.1`.
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Note that the regex pattern is enclosed in single quotes, and backslashes are escaped with backslashes.
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```
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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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```
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## Expressions
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To evaluate expressions, *view* uses the antonmedv/expr package (https://github.com/antonmedv/expr).
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For example, an expression could look like:
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`(type() == 'A' && name() == 'example.com') || client_ip() == '1.2.3.4'`.
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All expressions should be written to evaluate to a boolean value.
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See https://github.com/antonmedv/expr/blob/master/docs/Language-Definition.md as a detailed reference for valid syntax.
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### Available Expression Functions
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In the context of the *view* plugin, expressions can reference DNS query information by using utility
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functions defined below.
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#### DNS Query Functions
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* `bufsize() int`: the EDNS0 buffer size advertised in the query
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* `class() string`: class of the request (IN, CH, ...)
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* `client_ip() string`: client's IP address, for IPv6 addresses these are enclosed in brackets: `[::1]`
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* `do() bool`: the EDNS0 DO (DNSSEC OK) bit set in the query
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* `id() int`: query ID
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* `name() string`: name of the request (the domain name requested)
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* `opcode() int`: query OPCODE
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* `port() string`: client's port
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* `proto() string`: protocol used (tcp or udp)
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* `server_ip() string`: server's IP address; for IPv6 addresses these are enclosed in brackets: `[::1]`
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* `server_port() string` : server's port
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* `size() int`: request size in bytes
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* `type() string`: type of the request (A, AAAA, TXT, ...)
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#### Utility Functions
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* `incidr(ip string, cidr string) bool`: returns true if _ip_ is within _cidr_
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* `metadata(label string)` - returns the value for the metadata matching _label_
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## Metadata
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The view plugin will publish the following metadata, if the *metadata*
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plugin is also enabled:
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* `view/name`: the name of the view handling the current request
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