| // |
| // 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. |
| // |
| |
| === HTTP Balancer |
| |
| Apache Karaf Cellar is able to expose servlets local to a node on the cluster. |
| It means that a client (browser) can use any node in the cluster, proxying the requests to the node actually |
| hosting the servlets. |
| |
| ==== Enable HTTP Balancer |
| |
| To enable Cellar HTTP Balancer, you have to first install the `http` and `http-whiteboard` features: |
| |
| ---- |
| karaf@root()> feature:install http |
| karaf@root()> feature:install http-whiteboard |
| ---- |
| |
| Now, we install the `cellar-http-balancer` feature, actually providing the balancer: |
| |
| ---- |
| karaf@root()> feature:install cellar-http-balancer |
| ---- |
| |
| Of course, you can use Cellar to spread the installation of the `cellar-http-balancer` feature on all nodes in the |
| cluster group: |
| |
| ---- |
| karaf@root()> cluster:feature-install default cellar-http-balancer |
| ---- |
| |
| It's done: the Cellar HTTP Balancer is now enabled. It will expose proxy servlets on nodes. |
| |
| ==== Balancer in action |
| |
| To illustrate Cellar HTTP Balancer in action, you need at least a cluster with two nodes. |
| |
| On node1, we enable the Cellar HTTP Balancer: |
| |
| ---- |
| karaf@node1()> feature:install http |
| karaf@node1()> feature:install http-whiteboard |
| karaf@node1()> feature:repo-add cellar 4.0.0 |
| karaf@node1()> feature:install cellar |
| karaf@node1()> cluster:feature-install default cellar-http-balancer |
| ---- |
| |
| Now, we install the webconsole on node1: |
| |
| ---- |
| karaf@node1()> feature:install webconsole |
| ---- |
| |
| We can see the "local" servlets provided by the webconsole feature using the `http:list` command: |
| |
| ---- |
| karaf@node1()> http:list |
| ID | Servlet | Servlet-Name | State | Alias | Url |
| ------------------------------------------------------------------------------------------------------ |
| 101 | KarafOsgiManager | ServletModel-2 | Undeployed | /system/console | [/system/console/*] |
| 103 | GogoPlugin | ServletModel-7 | Deployed | /gogo | [/gogo/*] |
| 102 | FeaturesPlugin | ServletModel-6 | Deployed | /features | [/features/*] |
| 101 | ResourceServlet | /res | Deployed | /system/console/res | [/system/console/res/*] |
| 101 | KarafOsgiManager | ServletModel-11 | Deployed | /system/console | [/system/console/*] |
| 105 | InstancePlugin | ServletModel-9 | Deployed | /instance | [/instance/*] |
| ---- |
| |
| You can access to the webconsole using a browser on http://localhost:8181/system/console. |
| |
| We can see that Cellar HTTP Balancer exposed the servlets to the cluster, using the `cluster:http-list` command: |
| |
| ---- |
| karaf@node1()> cluster:http-list default |
| Alias | Locations |
| ----------------------------------------------------------------- |
| /system/console/res | http://172.17.42.1:8181/system/console/res |
| /gogo | http://172.17.42.1:8181/gogo |
| /instance | http://172.17.42.1:8181/instance |
| /system/console | http://172.17.42.1:8181/system/console |
| /features | http://172.17.42.1:8181/features |
| ---- |
| |
| On another node (node2), we install `http`, `http-whiteboard` and `cellar` features: |
| |
| ---- |
| karaf@node1()> feature:install http |
| karaf@node1()> feature:install http-whiteboard |
| karaf@node1()> feature:repo-add cellar 4.0.0 |
| karaf@node1()> feature:install cellar |
| ---- |
| |
| [NOTE] |
| ==== |
| If you run the nodes on a single machine, you have to provision `etc/org.ops4j.pax.web.cfg` configuration file |
| containing the `org.osgi.service.http.port property` with a port number different to 8181. |
| For this example, we use the following `etc/org.ops4j.pax.web.cfg` file: |
| |
| ---- |
| org.osgi.service.http.port=8041 |
| ---- |
| ==== |
| |
| On node1, as we installed the `cellar-http-balancer` using `cluster:feature-install` command, it's automatically installed |
| when node2 joins the default cluster group. |
| |
| We can see the HTTP endpoints available on the cluster using the `cluster:http-list` command: |
| |
| ---- |
| karaf@node2()> cluster:http-list default |
| Alias | Locations |
| ----------------------------------------------------------------- |
| /system/console/res | http://172.17.42.1:8181/system/console/res |
| /gogo | http://172.17.42.1:8181/gogo |
| /instance | http://172.17.42.1:8181/instance |
| /system/console | http://172.17.42.1:8181/system/console |
| /features | http://172.17.42.1:8181/features |
| ---- |
| |
| If we take a look on the HTTP endpoints locally available on node2 (using `http:list` command), we can see the proxies |
| created by Cellar HTTP Balancer: |
| |
| ---- |
| karaf@node2()> http:list |
| ID | Servlet | Servlet-Name | State | Alias | Url |
| --------------------------------------------------------------------------------------------------------------- |
| 100 | CellarBalancerProxyServlet | ServletModel-3 | Deployed | /gogo | [/gogo/*] |
| 100 | CellarBalancerProxyServlet | ServletModel-2 | Deployed | /system/console/res | [/system/console/res/*] |
| 100 | CellarBalancerProxyServlet | ServletModel-6 | Deployed | /features | [/features/*] |
| 100 | CellarBalancerProxyServlet | ServletModel-5 | Deployed | /system/console | [/system/console/*] |
| 100 | CellarBalancerProxyServlet | ServletModel-4 | Deployed | /instance | [/instance/*] |
| ---- |
| |
| You can use a browser on http://localhost:8041/system/console: you will actually use the webconsole from node1, as |
| Cellar HTTP Balancer proxies from node2 to node1. |
| |
| Cellar HTTP Balancer randomly chooses one endpoint providing the HTTP endpoint. |
