Container

Working with Containers

A Container is an instance of a Gravia Runtime.

The set of supported target containers includes but is not limited to

• Apache Karaf
• Apache Tomcat
• JBoss WildFly

A Container has the following properties.

• It is uniquely identified in the cluster by a ContainerIdentity
• It has a current runtime State
• It has a set of typed Attributes
• It is associated with a specific Host
• It may have a parent Container
• It is associated with a ProfileVersion
• It is associated with a list of Profiles
• It has a set of Management Domains
• It has a set of ServiceEndpoints

Clients can obtain instances of containers from the ContainerManager.

Managing Containers

The ContainerManager is the central entry point for working with containers. It containers operations to

• Create, start, stop and destroy containers
• Find containers by given identifiers
• Associate a container with a given ProfileVersion
• Associate a container with a list of given Profiles
• Join/leave the Fabric8 cluster

Container instances returned by the ContainerManager are shallow immutable objects. They represent the state of physical containers at a moment in time.

Creating a Container

When Fabric8 bootstraps it automatically creates the current container. This would be a Tomcat, WildFly, Karaf container depending on the Fabric8 distribution that you bootstrap.

To create another Container from the current Container, you would use a ContainerBuilder and pass the so built CreateOptions to the ContainerManager like this

// Building the create options
KarafContainerBuilder builder = KarafContainerBuilder.create();
CreateOptions options = builder.build();

ContainerManager manager = ContainerManagerLocator.getContainerManager();
Container container = manager.createContainer(options);

The set of supported managed containers is

• TomcatManagedContainer
• WildFlyManagedContainer
• KarafManagedContainer

Creating a container provisions the default Profile

Starting/Stopping a Container

// Starting the container
ContainerManager manager = ContainerManagerLocator.getContainerManager();
container = manager.startContainer(container.getIdentity());

// Stopping the container
container = manager.stopContainer(container.getIdentity());

Destroying a Container

// Destroying the container
ContainerManager manager = ContainerManagerLocator.getContainerManager();
container = manager.destroyContainer(container.getIdentity());

A container that has associated child containers cannot be destroyed.

Concurrency and Locking Strategy

• Read access to Containers can happen concurrently.
• Each Container supports the notion of a read-write lock.
• A client may explicitly acquire a write lock for a Container.
• Obtaining a write lock for a Container also obtains a write lock on the associated ProfileVersion

Obtaining an exclusive lock on a Container is necessary when consistent access to Container content is required over a number of calls. For example when a Container is provisioned with Profile content it must be guaranteed that the Profile does not change and that no other lifecycle operations can be called on the Container.