DNS

Since Camel 2.7

Only producer is supported

This is an additional component for Camel to run DNS queries, using DNSJava. The component is a thin layer on top of 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

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:

<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

dns://operation[?options]

Configuring Options

Camel components are configured on two separate levels:

  • component level

  • endpoint level

Configuring Component Options

The component level is the highest level which holds general and common configurations that are inherited by the endpoints. For example a component may have security settings, credentials for authentication, urls for network connection and so forth.

Some components only have a few options, and others may have many. Because components typically have pre configured defaults that are commonly used, then you may often only need to configure a few options on a component; or none at all.

Configuring components can be done with the Component DSL, in a configuration file (application.properties|yaml), or directly with Java code.

Configuring Endpoint Options

Where you find yourself configuring the most is on endpoints, as endpoints often have many options, which allows you to configure what you need the endpoint to do. The options are also categorized into whether the endpoint is used as consumer (from) or as a producer (to), or used for both.

Configuring endpoints is most often done directly in the endpoint URI as path and query parameters. You can also use the Endpoint DSL and DataFormat DSL as a type safe way of configuring endpoints and data formats in Java.

A good practice when configuring options is to use Property Placeholders, which allows to not hardcode urls, port numbers, sensitive information, and other settings. In other words placeholders allows to externalize the configuration from your code, and gives more flexibility and reuse.

The following two sections lists all the options, firstly for the component followed by the endpoint.

Component Options

The DNS component supports 2 options, which are listed below.

Name Description Default Type

lazyStartProducer (producer)

Whether the producer should be started lazy (on the first message). By starting lazy you can use this to allow CamelContext and routes to startup in situations where a producer may otherwise fail during starting and cause the route to fail being started. By deferring this startup to be lazy then the startup failure can be handled during routing messages via Camel’s routing error handlers. Beware that when the first message is processed then creating and starting the producer may take a little time and prolong the total processing time of the processing.

false

boolean

autowiredEnabled (advanced)

Whether autowiring is enabled. This is used for automatic autowiring options (the option must be marked as autowired) by looking up in the registry to find if there is a single instance of matching type, which then gets configured on the component. This can be used for automatic configuring JDBC data sources, JMS connection factories, AWS Clients, etc.

true

boolean

Endpoint Options

The DNS endpoint is configured using URI syntax:

dns:dnsType

with the following path and query parameters:

Path Parameters (1 parameters)

Name Description Default Type

dnsType (producer)

Required The type of the lookup.

Enum values:

  • dig

  • ip

  • lookup

  • wikipedia

DnsType

Query Parameters (1 parameters)

Name Description Default Type

lazyStartProducer (producer (advanced))

Whether the producer should be started lazy (on the first message). By starting lazy you can use this to allow CamelContext and routes to startup in situations where a producer may otherwise fail during starting and cause the route to fail being started. By deferring this startup to be lazy then the startup failure can be handled during routing messages via Camel’s routing error handlers. Beware that when the first message is processed then creating and starting the producer may take a little time and prolong the total processing time of the processing.

false

boolean

Message Headers

The DNS component supports 6 message header(s), which is/are listed below:

Name Description Default Type

dns.class (lookup dig)

Constant: DNS_CLASS

The DNS class of the lookup. Should match the values of org.xbill.dns.DClass. Optional.

String

dns.name (lookup)

Constant: DNS_NAME

Required The name to lookup.

String

dns.domain (ip)

Constant: DNS_DOMAIN

Required The domain name.

String

dns.server (dig)

Constant: DNS_SERVER

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

String

dns.type (lookup dig)

Constant: DNS_TYPE

The type of the lookup. Should match the values of org.xbill.dns.Type. Optional.

String

term (wikipedia)

Constant: TERM

Required The term.

Examples

IP lookup

<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

<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.

<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.

 <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>