[[dns-component]]
== DNS Component

*Available as of Camel version 2.7*

This is an additional component for Camel to run DNS queries, using
DNSJava. The component is a thin layer on top of
http://www.xbill.org/dnsjava/[DNSJava]. +
 The component offers the following operations:

* ip, to resolve a domain by its ip
* lookup, to lookup information about the domain
* dig, to run DNS queries

INFO:*Requires SUN JVM*
The DNSJava library requires running on the SUN JVM. +
 If you use Apache ServiceMix or Apache Karaf, you'll need to adjust the
`etc/jre.properties` file, to add `sun.net.spi.nameservice` to the list
of Java platform packages exported. The server will need restarting
before this change takes effect.

Maven users will need to add the following dependency to their `pom.xml`
for this component:

[source,xml]
----
<dependency>
    <groupId>org.apache.camel</groupId>
    <artifactId>camel-dns</artifactId>
    <version>x.x.x</version>
    <!-- use the same version as your Camel core version -->
</dependency>
----

=== URI format

The URI scheme for a DNS component is as follows

[source,java]
-------------------------
dns://operation[?options]
-------------------------

This component only supports producers.

=== Options


// component options: START
The DNS component has no options.
// component options: END



// endpoint options: START
The DNS endpoint is configured using URI syntax:

----
dns:dnsType
----

with the following path and query parameters:

==== Path Parameters (1 parameters):


[width="100%",cols="2,5,^1,2",options="header"]
|===
| Name | Description | Default | Type
| *dnsType* | *Required* The type of the lookup. |  | DnsType
|===


==== Query Parameters (1 parameters):


[width="100%",cols="2,5,^1,2",options="header"]
|===
| Name | Description | Default | Type
| *synchronous* (advanced) | Sets whether synchronous processing should be strictly used, or Camel is allowed to use asynchronous processing (if supported). | false | boolean
|===
// endpoint options: END
// spring-boot-auto-configure options: START
=== Spring Boot Auto-Configuration

When using Spring Boot make sure to use the following Maven dependency to have support for auto configuration:

[source,xml]
----
<dependency>
  <groupId>org.apache.camel</groupId>
  <artifactId>camel-dns-starter</artifactId>
  <version>x.x.x</version>
  <!-- use the same version as your Camel core version -->
</dependency>
----


The component supports 2 options, which are listed below.



[width="100%",cols="2,5,^1,2",options="header"]
|===
| Name | Description | Default | Type
| *camel.component.dns.enabled* | Enable dns component | true | Boolean
| *camel.component.dns.resolve-property-placeholders* | Whether the component should resolve property placeholders on itself when starting. Only properties which are of String type can use property placeholders. | true | Boolean
|===
// spring-boot-auto-configure options: END



=== Headers
[width="100%",cols="10%,10%,10%,70%",options="header",]
|===

|Header |Type |Operations |Description

|dns.domain |String |ip |The domain name. Mandatory.

|dns.name |String |lookup |The name to lookup. Mandatory.

|dns.type |   | lookup, dig |The type of the lookup. Should match the values of `org.xbill.dns.Type`.
Optional.

|dns.class |   | lookup, dig |The DNS class of the lookup. Should match the values of
`org.xbill.dns.DClass`. Optional.

|dns.query |String |dig |The query itself. Mandatory.

|dns.server |String |dig |The server in particular for the query. If none is given, the default
one specified by the OS will be used. Optional.
|===

=== Examples

==== IP lookup

[source,xml]
----
        <route id="IPCheck">
            <from uri="direct:start"/>
            <to uri="dns:ip"/>
        </route>
----

This looks up a domain's IP. For example, www.example.com resolves to
192.0.32.10. +
 The IP address to lookup must be provided in the header with key
`"dns.domain"`.

==== DNS lookup

[source,xml]
----
        <route id="IPCheck">
            <from uri="direct:start"/>
            <to uri="dns:lookup"/>
        </route>
----

This returns a set of DNS records associated with a domain. +
 The name to lookup must be provided in the header with key
`"dns.name"`.

==== DNS Dig

Dig is a Unix command-line utility to run DNS queries.

[source,xml]
----
        <route id="IPCheck">
            <from uri="direct:start"/>
            <to uri="dns:dig"/>
        </route>
----

The query must be provided in the header with key `"dns.query"`.


=== Dns Activation Policy

DnsActivationPolicy can be used to dynamically start and stop routes based on dns state.

If you have instances of the same component running in different regions you can configure a route in each region to activate only if dns is pointing to its region.

i.e. You may have an instance in NYC and an instance in SFO. You would configure a service CNAME service.example.com to point to nyc-service.example.com to bring NYC instance up and SFO instance down. When you change the CNAME service.example.com to point to sfo-service.example.com -- nyc instance would stop its routes and sfo will bring its routes up. This allows you to switch regions without restarting actual components.

[source,xml]
----
	<bean id="dnsActivationPolicy" class="org.apache.camel.component.dns.policy.DnsActivationPolicy">
		<property name="hostname" value="service.example.com" />
		<property name="resolvesTo" value="nyc-service.example.com" />
		<property name="ttl" value="60000" />
		<property name="stopRoutesOnException" value="false" />
	</bean>

	<route id="routeId" autoStartup="false" routePolicyRef="dnsActivationPolicy">
	</route>
----
