| // |
| // Licensed under the Apache License, Version 2.0 (the "License"); |
| // you may not use this file except in compliance with the License. |
| // You may obtain a copy of the License at |
| // |
| // http://www.apache.org/licenses/LICENSE-2.0 |
| // |
| // Unless required by applicable law or agreed to in writing, software |
| // distributed under the License is distributed on an "AS IS" BASIS, |
| // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| // See the License for the specific language governing permissions and |
| // limitations under the License. |
| // |
| |
| === Introduction |
| |
| ==== Use Cases |
| |
| The first goal of Karaf Cellar is to synchronize the status of several Karaf instances (named nodes). |
| |
| Cellar provides dedicated shell commands and JMX MBeans to manage the cluster, and manipulate the resources on the cluster. |
| |
| It's also possible to enable local resources listeners: these listeners broadcast local resource changes as cluster events. |
| Please note that this behavior is disabled by default as it can have side effects (especially when a node is stopped). |
| Enabling listeners is at your own risk. |
| |
| The nodes list could be discovered (using unicast or multicast), or else defined in a static way (using a hostname/IP |
| and port list). |
| |
| Cellar is able to synchronize: |
| |
| * bundles (remote or local) |
| * config |
| * features |
| |
| Optionally, Cellar also supports synchronization of OSGi EventAdmin, OBR (URLs and bundles). |
| |
| The second goal is to provide a Distributed OSGi runtime. It means that using Cellar, you are able to call an OSGi |
| service located on a remote instance. See the link:transport[transport and DOSGi section] of the user guide. |
| |
| Finally, Cellar also provides "runtime clustering" by providing dedicated features like: |
| |
| * HTTP load balancing |
| * HTTP sessions replication |
| * log centralization |
| |
| Please, see the sections dedicated to those features. |
| |
| ==== Cross topology |
| |
| This is the default Cellar topology. Cellar is installed on all nodes, each node has the same function. |
| |
| It means that you can perform actions on any node, it will be broadcast to all other nodes. |
| |
| ==== Star topology |
| |
| In this topology, if Cellar is installed on all nodes, you perform actions only on one specific node (the "manager"). |
| |
| To do that, the "manager" is a standard Cellar node, and the event producing is disabled on all other nodes |
| (`cluster:producer-stop` on all "managed" nodes). |
| |
| Like this, only the "manager" will send event to the nodes (which are able to consume and handle), but no event can |
| be produced on the nodes. |
