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Learning Karaf Cellar
Learning Karaf Cellar

Learning Karaf Cellar: Build and implement a complete clustering solution for the Apache Karaf OSGi container

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Profile Icon Jean-Baptiste Onofré Profile Icon Jean Baptiste Onofre
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Arrow left icon
Profile Icon Jean-Baptiste Onofré Profile Icon Jean Baptiste Onofre
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Paperback Jul 2014 124 pages 1st Edition
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Learning Karaf Cellar

Chapter 2. Apache Karaf Cellar

Apache Karaf Cellar is a provisioning cluster solution for Apache Karaf.

It's an Apache Karaf subproject released under the Apache 2 license. To know more, please visit http://karaf.apache.org/index/subprojects/cellar.html.

Apache Karaf Cellar allows you to manage a farm of Apache Karaf instances spread over different machines and networks.

As a provisioning cluster solution, Apache Karaf Cellar synchronizes the states of the different instances. By synchronization, we mean that an action on a resource from a node will result in a notification to change for the other nodes.

The following topics will be covered in this chapter:

  • Cluster topologies
  • Apache Karaf Cellar architecture
  • Apache Karaf Cellar installation
  • Cluster resources

Cluster topologies

When we talk about provisioning clusters, it means that we have to store and share the status of resources between different instances.

We name the node as an instance member of the provisioning cluster.

We can see two approaches to share the status of the resources.

The first approach is to use a central component to store the status. This central component is named cluster manager. It's responsible for storing the data shared between the nodes and the communication between the nodes. Have a look at the following diagram:

Cluster topologies

All nodes are connected to a central component storing the status of the resources. For instance, this component could be Apache ZooKeeper.

The advantage of this approach is that the provisioning cluster has no impact on the nodes; a node just communicates with the central component.

The cluster manager is not just a simple shared storage, as it has to deal with the communication and transport of information between the nodes.

A drawback of this approach...

Apache Karaf Cellar architecture

Apache Karaf Cellar provides an API to implement the cluster component. The default cluster component implementation is powered by Hazelcast.

Hazelcast is a clustering and scalable data distribution solution. It provides features that exactly match the needs for the cluster component, especially the following:

  • A distributed storage implementation. This is where Apache Karaf Cellar will store the resources' status.
  • A distributed topic for publish/subscribe messaging. Apache Karaf Cellar will use this distributed topic to implement cluster events.

These are the two functionalities we are looking for in our cluster component.

However, Hazelcast also provides additional features. Thanks to Hazelcast, Apache Karaf Cellar supports different ways to discover the nodes of the cluster: static IP address definition, multicast, and whiteboard registration. The following diagram shows the modules provided by Karaf:

Apache Karaf Cellar architecture

The first thing to do is install Cellar in the different...

Apache Karaf Cellar installation and first commands

Apache Karaf Cellar is provided as a Karaf feature.

Throughout this book, we will use the following installation:

  • Node 1 is a server running with the 192.168.1.1 network address. It hosts an Apache Karaf 2.3.3 instance running in the /opt/apache-karaf folder.
  • Node 2 is another server running with the 192.168.1.2 network address. It hosts an Apache Karaf 2.3.3 instance running in the /opt/apache-karaf folder.
  • Both servers have Internet access.

We connect to the Apache Karaf instance on node 1 (using SSH or client) to install the Apache Karaf Cellar feature, as follows:

karaf@node1> features:addurl mvn:org.apache.karaf.cellar/apache-karaf-cellar/2.3.1/xml/features
karaf@node1> features:install cellar

It's done! Apache Karaf Cellar is installed and operating on node1.

We can now install Apache Karaf Cellar on node 2. We connect on node 2 (using SSH or client) and install the Apache Karaf Cellar feature, as follows:

karaf@node2> features...

Cluster resources

By default, Apache Karaf Cellar supports the clustering and distribution of different resources.

Cellar is able to manage the resources covered in the following sections.

Bundles

Apache Karaf Cellar is able to sync the status of OSGi bundles on the cluster.

Thanks to the bundle listener, all actions that you may perform on a bundle are spread onto the cluster. You can also use dedicated cluster commands to manipulate the bundles on the cluster.

For instance, it's possible to see the bundles available on the cluster with their current status using the cluster:bundle-list command as follows:

karaf@node1> cluster:bundle-list default
Bundles in cluster group default
 ID      State     Name
[0   ] [Active] Apache Karaf :: Cellar :: Utils (2.3.1)
[1   ] [Active] Apache Karaf :: JAAS :: Config (2.3.3)
[2   ] [Active] Apache Karaf :: Diagnostic :: Command (2.3.3)
[3   ] [Active] Apache Karaf :: Deployer :: Spring (2.3.3)
[4   ] [Active] Apache Aries Proxy Service (1.0.1)
[5...

Summary

In this chapter, we have introduced the Apache Karaf Cellar topology and architecture.

We also installed Apache Karaf Cellar and used some basic commands to sync two nodes in a cluster. The next chapter will describe the configuration files used by Apache Karaf Cellar and the usage of Hazelcast.

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Description

This book is a tutorial written with a step-by-step approach to help you implement an optimum clustering solution in Apache Karaf Cellar quickly and efficiently. If you are new to Karaf and want to install and manage multiple Karaf instances by farming or clustering, then this book is for you. If you are a Java developer or a system administrator with basic knowledge of Karaf, you can use this book as a guide. Some background knowledge of OSGi and/or Karaf would be preferred but is not mandatory.

What you will learn

  • Explore the Apache Karaf OSGi container and its features
  • Install and configure multiple Karaf containers
  • Leverage Hazelcast using Cellar to provide clustering
  • Create and manage multiple cluster groups
  • Discover the different components of Cellar and how to administrate them
  • Implement a finegrained topology by filtering cluster events
  • Use Cellar to implement remote communication between OSGi bundles (DOSGi)
  • Use Cellar with Camel to implement a remote communication between Camel routes and a distributed cache
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Length: 124 pages
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Table of Contents

10 Chapters
1. Apache Karaf – Provisioning and Clusters Chevron down icon Chevron up icon
2. Apache Karaf Cellar Chevron down icon Chevron up icon
3. Hazelcast Chevron down icon Chevron up icon
4. Cluster Groups Chevron down icon Chevron up icon
5. Producers, Consumers, Handlers, Listeners, and Synchronizers Chevron down icon Chevron up icon
6. The Filtering of Cluster Events Chevron down icon Chevron up icon
7. DOSGi Chevron down icon Chevron up icon
8. Cellar and Camel Chevron down icon Chevron up icon
9. Roadmap Chevron down icon Chevron up icon
Index Chevron down icon Chevron up icon

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Rodrigo Serra Dec 14, 2014
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Nice introductory book
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