11.4. Configuring Fabric Containers

Overview

When a container is part of a fabric, it does not manage its configuration. The container's configuration is managed by the Fabric Agent. The agent runs along with the container and updates the container's configuration based on information from the fabric's registry.
Because the configuration is managed by the Fabric Agent, any changes to the container's configuration needs to be done by updating the fabric's registry. In a fabric, container configuration is determined by one or more profiles that are deployed into the container. To change a container's configuration, you must update the profile(s) deployed into the container using either the console's fabric: shell or the management console.

Profiles

All configuration in a fabric is stored as profiles in the Fabric Registry. One or more profiles are assigned to containers that are part of the fabric. A profile is a collection of configuration that specifies:
  • the Apache Karaf features to be deployed
  • OSGi bundles to be deployed
  • the feature repositories to be scanned for features
  • properties that configure the container's runtime behavior
The configuration profiles are collected into versions. Versions are typically used to make updates to an existing profile without effecting deployed containers. When a container is configured it is assigned a profile version from which it draws the profiles. Therefore, when you create a new version and edit the profiles in the new version, the profiles that are in use are not changed. When you are ready to test the changes, you can roll them out incrementally by moving containers to a new version one at a time.
When a container joins a fabric, a Fabric Agent is deployed with the container and takes control of the container's configuration. The agent will ask the Fabric Registry what version and profile(s) are assigned to the container and configure the container based on the profiles. The agent will download and install of the specified bundles and features. It will also set all of the specified configuration properties.

Best practices

Editing a profile makes changes to the copy in the Fabric Registry and all of the Fabric Agents are alerted when changes are made. If a running container is using a profile that is changed, its agent will automatically apply the new settings. If the update is benign having the change rolled out to the entire fabric is not an issue. If, on the other hand, the change causes issues, the entire fabric could become unstable.
To avoid having untested changes infecting an entire fabric, you should always make a new version before editing a profile. This isolates the changes in a version that is not running on any containers and provides a quick backup in case the changes are bad.
Once the profile changes have been made, you should test them out by upgrading only a few containers to the new version to see how they behave. As you become confident that the changes are good, you can then upgrade more containers.

Making changes using the command console

The command console's fabric shell has commands for managing profiles and versions in a fabric. These commands include:
  • fabric:version-create—create a new version
  • fabric:profile-create—create a new profile
  • fabric:profile-edit—edit the properties in a profile
  • fabric:container-change-profile—change the profiles assigned to a container
Example 11.3, “Editing Fabric Profile” shows a session for updating a profile using the command console.

Example 11.3. Editing Fabric Profile

JBossFuse:karaf@root> fabric:version-create
Created version: 1.1 as copy of: 1.0
JBossFuse:karaf@root> fabric:profile-edit -p org.apache.karaf.log/size=300 NEBroker
The change made in Example 11.3, “Editing Fabric Profile” is not applied to any running containers because it is made in a new version. In order to apply the change you need to update one or more containers using the fabric:container-upgrade command.

Using the management console

The management console simplifies the process of configuring containers in a fabric by providing an easy to use Web-based interface and reducing the number of steps required to make the changes. For more information on using the management console see Using the Management Console.