def µsvc = Fabric8.apply(karaf).andThen(camel)

Fabric8 is an amazing microservice platform which not only provide all the building blocks needed to effectively impement microservices but also a number of high quality open-source libraries and tools that every developer could leverage to ease the integration with Kubernetes/OpenShift.

Some of the bits fabric8 provides are:

As we are brave, we won’t talk about doing Microservices with Spring Boot but we’ll go with Apache Karaf and Apache Camel.

Note	I’ll show the relevant parts here, full code is available on github

Set-up

In a traditional environment you often deploy bundles on a running Karaf container but that’s not the way we want to deploy in a microservice environment. Instead we want standalone applications so the first step is to create custom Karaf distribution pre-configured with the needed bundles.

This can be done via karaf-maven-plugin:

<plugin>
    <groupId>org.apache.karaf.tooling</groupId>
    <artifactId>karaf-maven-plugin</artifactId>
    <version>${karaf.version}</version>
    <extensions>true</extensions>
    <executions> (1)
      <execution>
        <id>karaf-assembly</id>
        <goals>
          <goal>assembly</goal>
        </goals>
        <phase>install</phase>
      </execution>
      <execution>
        <id>karaf-archive</id>
        <goals>
          <goal>archive</goal>
        </goals>
        <phase>install</phase>
      </execution>
    </executions>
    <configuration>
      <javase>1.8</javase>
      <archiveTarGz>true</archiveTarGz>
      <startupFeatures> (2)
        <!-- karaf -->
        <feature>framework</feature>
        <feature>scr</feature>
        <feature>aries-blueprint</feature>

        <!-- fabric8 -->
        <feature>fabric8-karaf-blueprint</feature>
        <feature>fabric8-karaf-cm</feature>

        <!-- camel -->
        <feature>camel-core</feature>
        <feature>camel-blueprint</feature>
      </startupFeatures>
      <startupBundles> (3)
        <bundle>mvn:${project.groupId}/${project.artifactId}/${project.version};start-level=80</bundle>
      </startupBundles>
    </configuration>
    ...
</plugin>

Map karaf-maven-plugin’s karaf-assembly and archive phases to install phase, this is mandatory if you want your project to be included in the distribution.
List of features to start at boot
List of bundles to start at boot

We are now ready to start writing our microservice so let’s have a look on how to leverage Fabric8 Karaf:

With fabric8-karaf-blueprint installed you can access ConfigMap and Secrets using property placeholders so if you have a ConfigMap like the one below

kind: ConfigMap
apiVersion: v1
metadata:
  name: camel-karaf-global
data:
  data.center.name: "dc1"

you can use the notation k8s:map:mapName/dataKey to retrieve the vaue of the field data.center.name, i.e:

<bean id="myBean" class="com.github.lburgazzoli.microservice.MyBean">
  <argument value="$[k8s:map:camel-karaf-global/data.center.name]"/>
  ...
</bean>

With fabric8-karaf-cm installed you can feed ConfigAdmin with values from ConfigMaps so if you have a ConfigMap as below
```
kind: ConfigMap
apiVersion: v1
metadata:
  name: camel-karaf-microservice
  labels:
    karaf.pid: camel.karaf.microservice
data:
  bean.body: "Hello from OpenShift"
```
then the service with pid camel.karaf.microservice will be able to retrieve the value of the property bean.body as if the value would have been provided in etc/camel.karaf.microservice.cfg:
```
<bean id="myBean" class="com.github.lburgazzoli.microservice.MyBean">
  ..
  <argument value="${bean.body}"/>
</bean>
```
With fabric8-karaf-cm installed you can "hot reconfigure" your application by updating a ConfigMap

So let’s put all togheter to implement a simple Camel route using OSGI Blueprint:

<?xml version="1.0"?>
<blueprint xmlns="http://www.osgi.org/xmlns/blueprint/v1.0.0"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xmlns:cm="http://aries.apache.org/blueprint/xmlns/blueprint-cm/v1.3.0"
  xmlns:ext="http://aries.apache.org/blueprint/xmlns/blueprint-ext/v1.3.0"
  xsi:schemaLocation="
    http://www.osgi.org/xmlns/blueprint/v1.0.0
    https://www.osgi.org/xmlns/blueprint/v1.0.0/blueprint.xsd
    http://camel.apache.org/schema/blueprint
    http://camel.apache.org/schema/blueprint/camel-blueprint.xsd
    http://aries.apache.org/blueprint/xmlns/blueprint-ext/v1.3.0
    http://aries.apache.org/schemas/blueprint-ext/blueprint-ext-1.3.xsd">

  <cm:property-placeholder
      persistent-id="camel.karaf.microservice" (1)
      update-strategy="reload"> (2)
    <cm:default-properties>
    </cm:default-properties>
  </cm:property-placeholder>

  <ext:property-placeholder
    evaluator="fabric8" (3)
    placeholder-prefix="$[" placeholder-suffix="]"/>

  <bean id="myBean" class="com.github.lburgazzoli.microservice.MyBean">
    <argument value="$[k8s:map:camel-karaf-global/data.center.name]"/>
    <argument value="${bean.body}"/>
  </bean>

  <camelContext id="camel-context" xmlns="http://camel.apache.org/schema/blueprint">

    <route id="timer">
      <from uri="timer:foo?period=10s"/>
      <setHeader headerName="DataCenter">
          <method ref="myBean" method="dataCenter"/>
      </setHeader>
      <setBody>
          <method ref="myBean" method="body"/>
      </setBody>
      <log message="Body is: ${body}, DataCenter is: ${header.DataCenter}"/>
    </route>

  </camelContext>

</blueprint>

Set the persistent-id for the Blueprint.
Configure reload strategy of the context so if a property changes in ConfigAdmin (i.e. by changing the related ConfigMap) the context will be reloaded.
Configure fabric8 PropertyEvaluator so that you can use Fabric8’s functions to resolve placeholders.

Note	Check the Fabric8 Karaf documentation for details and options.

Running the example

You need a running OpenShift or Kubenretes cluster to run the example, if you do not have one I suggest to use Minikube or Minishift to set up an environment in a few simple steps even while having a drink at the Airport

Important

If you deploy on OpenShift you need to grant view role to the service account oc policy add-role-to-user view system:serviceaccount:$(oc project -q):default -n $(oc project -q)

To run the application run the following command:

./mvnw clean fabric8:run

This command will build the application, generate OpenShift/Kubernetes resources then deploy and run the application to the cluster and finally tail the pod log so you can see what the application is doing.

After the initialization the log should looks like:

[INFO] F8: 2016-10-24 15:48:14,717 | INFO  | FelixStartLevel  | BlueprintCamelContext            | 36 - org.apache.camel.camel-core - 2.18.0 | Apache Camel 2.18.0 (CamelContext: camel-context) started in 0.284 seconds
[INFO] F8: 2016-10-24 15:48:15,728 | INFO  | #0 - timer://foo | timer                            | 36 - org.apache.camel.camel-core - 2.18.0 | Body is: Hello from OpenShift, DataCenter is: dc1
[INFO] F8: 2016-10-24 15:48:25,736 | INFO  | #0 - timer://foo | timer                            | 36 - org.apache.camel.camel-core - 2.18.0 | Body is: Hello from OpenShift, DataCenter is: dc1
[INFO] F8: 2016-10-24 15:48:35,718 | INFO  | #0 - timer://foo | timer                            | 36 - org.apache.camel.camel-core - 2.18.0 | Body is: Hello from OpenShift, DataCenter is: dc1

Now if we update the ConfigMap named camel-karaf-microservice with a message like Hello from Minishift we should see the context to be restarted and the new message being displayed like below:

[INFO] F8: 2016-10-24 15:50:01,214 | INFO  | Thread-9         | BlueprintCamelContext            | 36 - org.apache.camel.camel-core - 2.18.0 | Apache Camel 2.18.0 (CamelContext: camel-context) is shutting down
[INFO] F8: 2016-10-24 15:50:01,216 | INFO  | Thread-9         | DefaultShutdownStrategy          | 36 - org.apache.camel.camel-core - 2.18.0 | Starting to graceful shutdown 1 routes (timeout 300 seconds)
[INFO] F8: 2016-10-24 15:50:01,220 | INFO  | 1 - ShutdownTask | DefaultShutdownStrategy          | 36 - org.apache.camel.camel-core - 2.18.0 | Route: timer shutdown complete, was consuming from: timer://foo?period=10s
[INFO] F8: 2016-10-24 15:50:01,221 | INFO  | Thread-9         | DefaultShutdownStrategy          | 36 - org.apache.camel.camel-core - 2.18.0 | Graceful shutdown of 1 routes completed in 0 seconds
[INFO] F8: 2016-10-24 15:50:01,249 | INFO  | Thread-9         | BlueprintCamelContext            | 36 - org.apache.camel.camel-core - 2.18.0 | Apache Camel 2.18.0 (CamelContext: camel-context) uptime 1 minute
[INFO] F8: 2016-10-24 15:50:01,250 | INFO  | Thread-9         | BlueprintCamelContext            | 36 - org.apache.camel.camel-core - 2.18.0 | Apache Camel 2.18.0 (CamelContext: camel-context) is shutdown in 0.035 seconds
[INFO] F8: 2016-10-24 15:50:01,330 | INFO  | rint Extender: 1 | BlueprintCamelContext            | 36 - org.apache.camel.camel-core - 2.18.0 | Apache Camel 2.18.0 (CamelContext: camel-context) is starting
[INFO] F8: 2016-10-24 15:50:01,330 | INFO  | rint Extender: 1 | ManagedManagementStrategy        | 36 - org.apache.camel.camel-core - 2.18.0 | JMX is enabled
[INFO] F8: 2016-10-24 15:50:01,364 | INFO  | rint Extender: 1 | DefaultRuntimeEndpointRegistry   | 36 - org.apache.camel.camel-core - 2.18.0 | Runtime endpoint registry is in extended mode gathering usage statistics of all incoming and outgoing endpoints (cache limit: 1000)
[INFO] F8: 2016-10-24 15:50:01,396 | INFO  | rint Extender: 1 | BlueprintCamelContext            | 36 - org.apache.camel.camel-core - 2.18.0 | StreamCaching is not in use. If using streams then its recommended to enable stream caching. See more details at http://camel.apache.org/stream-caching.html
[INFO] F8: 2016-10-24 15:50:01,417 | INFO  | rint Extender: 1 | BlueprintCamelContext            | 36 - org.apache.camel.camel-core - 2.18.0 | Route: timer started and consuming from: timer://foo?period=10s
[INFO] F8: 2016-10-24 15:50:01,418 | INFO  | rint Extender: 1 | BlueprintCamelContext            | 36 - org.apache.camel.camel-core - 2.18.0 | Total 1 routes, of which 1 are started.
[INFO] F8: 2016-10-24 15:50:01,418 | INFO  | rint Extender: 1 | BlueprintCamelContext            | 36 - org.apache.camel.camel-core - 2.18.0 | Apache Camel 2.18.0 (CamelContext: camel-context) started in 0.087 seconds
[INFO] F8: 2016-10-24 15:50:02,419 | INFO  | #2 - timer://foo | timer                            | 36 - org.apache.camel.camel-core - 2.18.0 | Body is: Hello from Minishift, DataCenter is: dc1
[INFO] F8: 2016-10-24 15:50:12,418 | INFO  | #2 - timer://foo | timer                            | 36 - org.apache.camel.camel-core - 2.18.0 | Body is: Hello from Minishift, DataCenter is: dc1
[INFO] F8: 2016-10-24 15:50:22,419 | INFO  | #2 - timer://foo | timer                            | 36 - org.apache.camel.camel-core - 2.18.0 | Body is: Hello from Minishift, DataCenter is: dc1