//
// 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.
//

=== Provisioning

Apache Karaf supports the provisioning of applications and modules using the concept of Karaf Features.

==== Application

By provisioning application, it means install all modules, configuration, and transitive applications.

==== OSGi

It natively supports the deployment of OSGi applications.

An OSGi application is a set of OSGi bundles. An OSGi bundles is a regular jar file, with additional metadata in the jar MANIFEST.

In OSGi, a bundle can depend to other bundles. So, it means that to deploy an OSGi application, most of the time, you have
to firstly deploy a lot of other bundles required by the application.

So, you have to find these bundles first, install the bundles. Again, these "dependency" bundles may require other bundles
to satisfy their own dependencies.

More over, typically, an application requires configuration (see the [Configuration section|configuration] of the user guide).
So, before being able to start your application, in addition of the dependency bundles, you have to create or deploy the
configuration.

As we can see, the provisioning of an application can be very long and fastidious.

==== Feature and resolver

Apache Karaf provides a simple and flexible way to provision applications.

In Apache Karaf, the application provisioning is an Apache Karaf "feature".

A feature describes an application as:

* a name
* a version
* a optional description (eventually with a long description)
* a set of bundles
* optionally a set configurations or configuration files
* optionally a set of dependency features

When you install a feature, Apache Karaf installs all resources described in the feature. It means that it will
automatically resolves and installs all bundles, configurations, and dependency features described in the feature.

The feature resolver checks the service requirements, and install the bundles providing the services matching the requirements.
The default mode enables this behavior only for "new style" features repositories (basically, the features repositories XML with
schema equal or greater to 1.3.0). It doesn't apply for "old style" features repositories (coming from Karaf 2 or 3).

You can change the service requirements enforcement mode in `etc/org.apache.karaf.features.cfg` file, using the `serviceRequirements` property.

----
serviceRequirements=default
----

The possible values are:

* disable: service requirements are completely ignored, for both "old style" and "new style" features repositories
* default: service requirements are ignored for "old style" features repositories, and enabled for "new style" features repositories.
* enforce: service requirements are always verified, for "old style" and "new style" features repositories.

Additionally, a feature can also define requirements. In that case, Karaf can automatically additional bundles or features
providing the capabilities to satisfy the requirements.

A feature has a complete lifecycle: install, start, stop, update, uninstall.

==== Features repositories

The features are described in a features XML descriptor. This XML file contains the description of a set of features.

A features XML descriptor is named a "features repository". Before being able to install a feature, you have to register
the features repository that provides the feature (using `feature:repo-add` command or FeatureMBean as described later).

For instance, the following XML file (or "features repository") describes the `feature1` and `feature2` features:

----
<features xmlns="http://karaf.apache.org/xmlns/features/v1.3.0">
  <feature name="feature1" version="1.0.0">
    <bundle>...</bundle>
    <bundle>...</bundle>
  </feature>
  <feature name="feature2" version="1.1.0">
    <feature>feature1</feature>
    <bundle>...</bundle>
  </feature>
</features>
----

We can note that the features XML has a schema. Take a look on [Features XML Schema section|provisioning-schema] of the user guide
for details.
The `feature1` feature is available in version `1.0.0`, and contains two bundles. The `<bundle/>` element contains a URL
to the bundle artifact (see [Artifacts repositories and URLs section|urls] for details). If you install the `feature1` feature
(using `feature:install` or the FeatureMBean as described later), Apache Karaf will automatically installs the two bundles
described.
The `feature2` feature is available in version `1.1.0`, and contains a reference to the `feature1` feature and a bundle.
The `<feature/>` element contains the name of a feature. A specific feature version can be defined using the `version`
attribute to the `<feature/>` element (`<feature version="1.0.0">feature1</feature>`). If the `version` attribute is
not specified, Apache Karaf will install the latest version available. If you install the `feature2` feature (using `feature:install`
or the FeatureMBean as described later), Apache Karaf will automatically installs `feature1` (if it's not already installed)
and the bundle.

A feature repository is registered using the URL to the features XML file.

The features state is stored in the Apache Karaf cache (in the `KARAF_DATA` folder). You can restart Apache Karaf, the
previously installed features remain installed and available after restart.
If you do a clean restart or you delete the Apache Karaf cache (delete the `KARAF_DATA` folder), all previously features
repositories registered and features installed will be lost: you will have to register the features repositories and install
features by hand again.
To prevent this behaviour, you can specify features as boot features.

==== Boot features

You can describe some features as boot features. A boot feature will be automatically install by Apache Karaf, even if it has
not been previously installed using `feature:install` or FeatureMBean.

Apache Karaf features configuration is located in the `etc/org.apache.karaf.features.cfg` configuration file.

This configuration file contains the two properties to use to define boot features:

* `featuresRepositories` contains a list (comma-separated) of features repositories (features XML) URLs.
* `featuresBoot` contains a list (comma-separated) of features to install at boot.

==== Features upgrade

You can update a release by installing the same feature (with the same SNAPSHOT version or a different version).

Thanks to the features lifecycle, you can control the status of the feature (started, stopped, etc).

You can also use a simulation to see what the update will do.

==== Overrides

Bundles defined in features can be overridden by using a file etc/overrides.properties.
Each line in the file defines one override. The syntax is:
<bundle-uri>[;range="[min,max)"]
The given bundle will override all bundles in feature definitions with the same symbolic name if the version
of the override is greater than the version of the overridden bundle and the range matches.
If no range is given then compatibility on the micro version level is assumed.

So for example the override mvn:org.ops4j.pax.logging/pax-logging-service/1.8.5
would overide pax-logging-service 1.8.3 but not 1.8.6 or 1.7.0.

==== Feature bundles

===== Start Level

By default, the bundles deployed by a feature will have a start-level equals to the value defined in the `etc/config.properties`
configuration file, in the `karaf.startlevel.bundle` property.

This value can be "overrided" by the `start-level` attribute of the `<bundle/>` element, in the features XML.

----
  <feature name="my-project" version="1.0.0">
    <bundle start-level="80">mvn:com.mycompany.myproject/myproject-dao</bundle>
    <bundle start-level="85">mvn:com.mycompany.myproject/myproject-service</bundle>
  </feature>
----

The start-level attribute insure that the `myproject-dao` bundle is started before the bundles that use it.

Instead of using start-level, a better solution is to simply let the OSGi framework know what your dependencies are by
defining the packages or services you need. It is more robust than setting start levels.

===== Simulate, Start and stop

You can simulate the installation of a feature using the `-t` option to `feature:install` command.

You can install a bundle without starting it. By default, the bundles in a feature are automatically started.

A feature can specify that a bundle should not be started automatically (the bundle stays in resolved state).
To do so, a feature can specify the `start` attribute to false in the `<bundle/>` element:

----
  <feature name="my-project" version="1.0.0">
    <bundle start-level="80" start="false">mvn:com.mycompany.myproject/myproject-dao</bundle>
    <bundle start-level="85" start="false">mvn:com.mycompany.myproject/myproject-service</bundle>
  </feature>
----

===== Dependency

A bundle can be flagged as being a dependency, using the `dependency` attribute set to true on the `<bundle/>` element.

This information can be used by resolvers to compute the full list of bundles to be installed.

==== Dependent features

A feature can depend to a set of other features:

----
  <feature name="my-project" version="1.0.0">
    <feature>other</feature>
    <bundle start-level="80" start="false">mvn:com.mycompany.myproject/myproject-dao</bundle>
    <bundle start-level="85" start="false">mvn:com.mycompany.myproject/myproject-service</bundle>
  </feature>
----

When the `my-project` feature will be installed, the `other` feature will be automatically installed as well.

It's possible to define a version range for a dependent feature:

----
<feature name="spring-dm">
  <feature version="[2.5.6,4)">spring</feature>
  ...
</feature>
----

The feature with the highest version available in the range will be installed.

If a single version is specified, the range will be considered open-ended.

If nothing is specified, the highest available will be installed.

To specify an exact version, use a closed range such as `[3.1,3.1]`.

===== Feature prerequisites

Prerequisite feature is special kind of dependency. If you will add `prerequisite` attribute to dependant feature tag then it will force installation and also activation of bundles in dependant feature before installation of actual feature. This may be handy in case if bundles enlisted in given feature are not using pre installed URL such `wrap` or `war`.

==== Feature configurations

The `<config/>` element in a feature XML allows a feature to create and/or populate a configuration (identified by a configuration PID).

----
<config name="com.foo.bar">
  myProperty = myValue
</config>
----

The `name` attribute of the `<config/>` element corresponds to the configuration PID (see the [Configuration section|configuration] for details).

The installation of the feature will have the same effect as dropping a file named `com.foo.bar.cfg` in the `etc` folder.

The content of the `<config/>` element is a set of properties, following the key=value standard.

==== Feature configuration files

Instead of using the `<config/>` element, a feature can specify `<configfile/>` elements.

----
<configfile finalname="/etc/myfile.cfg" override="false">URL</configfile>
----

Instead of directly manipulating the Apache Karaf configuration layer (as when using the `<config/>` element), the
`<configfile/>` element takes directly a file specified by a URL, and copy the file in the location specified by the
`finalname` attribute.

If not specified, the location is relative from the `KARAF_BASE` variable. It's also possible to use variable like
${karaf.home}, ${karaf.base}, ${karaf.etc}, or even system properties.

For instance:

----
<configfile finalname="${karaf.etc}/myfile.cfg" override="false">URL</configfile>
----

If the file is already present at the desired location it is kept and the deployment of the configuration file is skipped,
as a already existing file might contain customization. This behaviour can be overriden by `override` set to true.

The file URL is any URL supported by Apache Karaf (see the [Artifacts repositories and URLs|urls] of the user guide for details).

===== Requirements

A feature can also specify expected requirements. The feature resolver will try to satisfy the requirements. For that, it checks
the features and bundles capabilities and will automatically install the bundles to satisfy the requirements.

For instance, a feature can contain:

----
<requirement>osgi.ee;filter:=&quot;(&amp;(osgi.ee=JavaSE)(!(version&gt;=1.8)))&quot;</requirement>
----

The requirement specifies that the feature will work by only if the JDK version is not 1.8 (so basically 1.7).

The features resolver is also able to refresh the bundles when an optional dependency is satisfy, rewiring the optional import.

==== Commands

===== `feature:repo-list`

The `feature:repo-list` command lists all registered features repository:

----
karaf@root()> feature:repo-list
Repository               | URL
--------------------------------------------------------------------------------------
org.ops4j.pax.cdi-0.12.0 | mvn:org.ops4j.pax.cdi/pax-cdi-features/0.12.0/xml/features
org.ops4j.pax.web-4.1.4  | mvn:org.ops4j.pax.web/pax-web-features/4.1.4/xml/features
standard-4.0.0           | mvn:org.apache.karaf.features/standard/4.0.0/xml/features
enterprise-4.0.0         | mvn:org.apache.karaf.features/enterprise/4.0.0/xml/features
spring-4.0.0             | mvn:org.apache.karaf.features/spring/4.0.0/xml/features
----

Each repository has a name and the URL to the features XML.

Apache Karaf parses the features XML when you register the features repository URL (using `feature:repo-add` command
or the FeatureMBean as described later). If you want to force Apache Karaf to reload the features repository URL (and
so update the features definition), you can use the `-r` option:

----
karaf@root()> feature:repo-list -r
Reloading all repositories from their urls

Repository               | URL
--------------------------------------------------------------------------------------
org.ops4j.pax.cdi-0.12.0 | mvn:org.ops4j.pax.cdi/pax-cdi-features/0.12.0/xml/features
org.ops4j.pax.web-4.1.4  | mvn:org.ops4j.pax.web/pax-web-features/4.1.4/xml/features
standard-4.0.0           | mvn:org.apache.karaf.features/standard/4.0.0/xml/features
enterprise-4.0.0         | mvn:org.apache.karaf.features/enterprise/4.0.0/xml/features
spring-4.0.0             | mvn:org.apache.karaf.features/spring/4.0.0/xml/features
----

===== `feature:repo-add`

To register a features repository (and so having new features available in Apache Karaf), you have to use the
`feature:repo-add` command.

The `feature:repo-add` command requires the `name/url` argument. This argument accepts:

* a feature repository URL. It's an URL directly to the features XML file. Any URL described in the [Artifacts repositories and URLs section|urls]
 of the user guide is supported.
* a feature repository name defined in the `etc/org.apache.karaf.features.repos.cfg` configuration file.

The `etc/org.apache.karaf.features.repos.cfg` defines a list of "pre-installed/available" features repositories:

----
################################################################################
#
#    Licensed to the Apache Software Foundation (ASF) under one or more
#    contributor license agreements.  See the NOTICE file distributed with
#    this work for additional information regarding copyright ownership.
#    The ASF licenses this file to You 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
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#       http://www.apache.org/licenses/LICENSE-2.0
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#    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.
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################################################################################

#
# This file describes the features repository URL
# It could be directly installed using feature:repo-add command
#
enterprise=mvn:org.apache.karaf.features/enterprise/LATEST/xml/features
spring=mvn:org.apache.karaf.features/spring/LATEST/xml/features
cellar=mvn:org.apache.karaf.cellar/apache-karaf-cellar/LATEST/xml/features
cave=mvn:org.apache.karaf.cave/apache-karaf-cave/LATEST/xml/features
camel=mvn:org.apache.camel.karaf/apache-camel/LATEST/xml/features
camel-extras=mvn:org.apache-extras.camel-extra.karaf/camel-extra/LATEST/xml/features
cxf=mvn:org.apache.cxf.karaf/apache-cxf/LATEST/xml/features
cxf-dosgi=mvn:org.apache.cxf.dosgi/cxf-dosgi/LATEST/xml/features
cxf-xkms=mvn:org.apache.cxf.services.xkms/cxf-services-xkms-features/LATEST/xml
activemq=mvn:org.apache.activemq/activemq-karaf/LATEST/xml/features
jclouds=mvn:org.apache.jclouds.karaf/jclouds-karaf/LATEST/xml/features
openejb=mvn:org.apache.openejb/openejb-feature/LATEST/xml/features
wicket=mvn:org.ops4j.pax.wicket/features/LATEST/xml/features
hawtio=mvn:io.hawt/hawtio-karaf/LATEST/xml/features
pax-cdi=mvn:org.ops4j.pax.cdi/pax-cdi-features/LATEST/xml/features
pax-jdbc=mvn:org.ops4j.pax.jdbc/pax-jdbc-features/LATEST/xml/features
pax-jpa=mvn:org.ops4j.pax.jpa/pax-jpa-features/LATEST/xml/features
pax-web=mvn:org.ops4j.pax.web/pax-web-features/LATEST/xml/features
pax-wicket=mvn:org.ops4j.pax.wicket/pax-wicket-features/LATEST/xml/features
ecf=http://download.eclipse.org/rt/ecf/latest/site.p2/karaf-features.xml
decanter=mvn:org.apache.karaf.decanter/apache-karaf-decanter/LATEST/xml/features
----

You can directly provide a features repository name to the `feature:repo-add` command. For install, to install PAX JDBC, you can do:

----
karaf@root()> feature:repo-add pax-jdbc
Adding feature url mvn:org.ops4j.pax.jdbc/pax-jdbc-features/LATEST/xml/features
----

When you don't provide the optional `version` argument, Apache Karaf installs the latest version of the features repository available.
You can specify a target version with the `version` argument:

----
karaf@root()> feature:repo-add pax-jdbc 1.3.0
Adding feature url mvn:org.ops4j.pax.jdbc/pax-jdbc-features/1.3.0/xml/features
----

Instead of providing a features repository name defined in the `etc/org.apache.karaf.features.repos.cfg` configuration file,
you can directly provide the features repository URL to the `feature:repo-add` command:

----
karaf@root()> feature:repo-add mvn:org.ops4j.pax.jdbc/pax-jdbc-features/1.3.0/xml/features
Adding feature url mvn:org.ops4j.pax.jdbc/pax-jdbc-features/1.3.0/xml/features
----

By default, the `feature:repo-add` command just registers the features repository, it doesn't install any feature.
If you specify the `-i` option, the `feature:repo-add` command registers the features repository and installs all
features described in this features repository:

----
karaf@root()> feature:repo-add -i pax-jdbc
----

===== `feature:repo-refresh`

Apache Karaf parses the features repository XML when you register it (using `feature:repo-add` command or the FeatureMBean).
If the features repository XML changes, you have to indicate to Apache Karaf to refresh the features repository to load the changes.

The `feature:repo-refresh` command refreshes the features repository.

Without argument, the command refreshes all features repository:

----
karaf@root()> feature:repo-refresh
Refreshing feature url mvn:org.ops4j.pax.cdi/pax-cdi-features/0.12.0/xml/features
Refreshing feature url mvn:org.ops4j.pax.web/pax-web-features/4.1.4/xml/features
Refreshing feature url mvn:org.apache.karaf.features/standard/4.0.0/xml/features
Refreshing feature url mvn:org.apache.karaf.features/enterprise/4.0.0/xml/features
Refreshing feature url mvn:org.apache.karaf.features/spring/4.0.0/xml/features
----

Instead of refreshing all features repositories, you can specify the features repository to refresh, by providing the URL
or the features repository name (and optionally version):

----
karaf@root()> feature:repo-refresh mvn:org.apache.karaf.features/standard/4.0.0/xml/features
Refreshing feature url mvn:org.apache.karaf.features/standard/4.0.0/xml/features
----

----
karaf@root()> feature:repo-refresh pax-jdbc
Refreshing feature url mvn:org.ops4j.pax.jdbc/pax-jdbc-features/LATEST/xml/features
----

===== `feature:repo-remove`

The `feature:repo-remove` command removes a features repository from the registered ones.

The `feature:repo-remove` command requires an argument:

* the features repository name (as displayed in the repository column of the `feature:repo-list` command output)
* the features repository URL (as displayed in the URL column of the `feature:repo-list` command output)

----
karaf@root()> feature:repo-remove org.ops4j.pax.jdbc-1.3.0
----

----
karaf@root()> feature:repo-remove mvn:org.ops4j.pax.jdbc/pax-jdbc-features/1.3.0/xml/features
----

By default, the `feature:repo-remove` command just removes the features repository from the registered ones: it doesn't
uninstall the features provided by the features repository.

If you use `-u` option, the `feature:repo-remove` command uninstalls all features described by the features repository:

----
karaf@root()> feature:repo-remove -u org.ops4j.pax.jdbc-1.3.0
----

===== `feature:list`

The `feature:list` command lists all available features (provided by the different registered features repositories):

----
Name                          | Version                          | Required | State       | Repository               | Description
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------
pax-cdi                       | 0.12.0                           |          | Uninstalled | org.ops4j.pax.cdi-0.12.0 | Provide CDI support
pax-cdi-1.1                   | 0.12.0                           |          | Uninstalled | org.ops4j.pax.cdi-0.12.0 | Provide CDI 1.1 support
pax-cdi-1.2                   | 0.12.0                           |          | Uninstalled | org.ops4j.pax.cdi-0.12.0 | Provide CDI 1.2 support
pax-cdi-weld                  | 0.12.0                           |          | Uninstalled | org.ops4j.pax.cdi-0.12.0 | Weld CDI support
pax-cdi-1.1-weld              | 0.12.0                           |          | Uninstalled | org.ops4j.pax.cdi-0.12.0 | Weld CDI 1.1 support
pax-cdi-1.2-weld              | 0.12.0                           |          | Uninstalled | org.ops4j.pax.cdi-0.12.0 | Weld CDI 1.2 support
pax-cdi-openwebbeans          | 0.12.0                           |          | Uninstalled | org.ops4j.pax.cdi-0.12.0 | OpenWebBeans CDI support
pax-cdi-web                   | 0.12.0                           |          | Uninstalled | org.ops4j.pax.cdi-0.12.0 | Web CDI support
pax-cdi-1.1-web               | 0.12.0                           |          | Uninstalled | org.ops4j.pax.cdi-0.12.0 | Web CDI 1.1 support
...
----

If you want to order the features by alphabetical name, you can use the `-o` option:

----
karaf@root()> feature:list -o
Name                          | Version                          | Required | State       | Repository               | Description
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------
deltaspike-core               | 1.2.1                            |          | Uninstalled | org.ops4j.pax.cdi-0.12.0 | Apache Deltaspike core support
deltaspike-data               | 1.2.1                            |          | Uninstalled | org.ops4j.pax.cdi-0.12.0 | Apache Deltaspike data support
deltaspike-jpa                | 1.2.1                            |          | Uninstalled | org.ops4j.pax.cdi-0.12.0 | Apache Deltaspike jpa support
deltaspike-partial-bean       | 1.2.1                            |          | Uninstalled | org.ops4j.pax.cdi-0.12.0 | Apache Deltaspike partial bean support
pax-cdi                       | 0.12.0                           |          | Uninstalled | org.ops4j.pax.cdi-0.12.0 | Provide CDI support
pax-cdi-1.1                   | 0.12.0                           |          | Uninstalled | org.ops4j.pax.cdi-0.12.0 | Provide CDI 1.1 support
pax-cdi-1.1-web               | 0.12.0                           |          | Uninstalled | org.ops4j.pax.cdi-0.12.0 | Web CDI 1.1 support
pax-cdi-1.1-web-weld          | 0.12.0                           |          | Uninstalled | org.ops4j.pax.cdi-0.12.0 | Weld Web CDI 1.1 support
pax-cdi-1.1-weld              | 0.12.0                           |          | Uninstalled | org.ops4j.pax.cdi-0.12.0 | Weld CDI 1.1 support
pax-cdi-1.2                   | 0.12.0                           |          | Uninstalled | org.ops4j.pax.cdi-0.12.0 | Provide CDI 1.2 support
...
----

By default, the `feature:list` command displays all features, whatever their current state (installed or not installed).

Using the `-i` option displays only installed features:

----
karaf@root()> feature:list -i
Name            | Version | Required | State   | Repository     | Description
-------------------------------------------------------------------------------------------------------------------
aries-proxy     | 4.0.0   |          | Started | standard-4.0.0 | Aries Proxy
aries-blueprint | 4.0.0   | x        | Started | standard-4.0.0 | Aries Blueprint
feature         | 4.0.0   | x        | Started | standard-4.0.0 | Features Support
shell           | 4.0.0   | x        | Started | standard-4.0.0 | Karaf Shell
shell-compat    | 4.0.0   | x        | Started | standard-4.0.0 | Karaf Shell Compatibility
deployer        | 4.0.0   | x        | Started | standard-4.0.0 | Karaf Deployer
bundle          | 4.0.0   | x        | Started | standard-4.0.0 | Provide Bundle support
config          | 4.0.0   | x        | Started | standard-4.0.0 | Provide OSGi ConfigAdmin support
diagnostic      | 4.0.0   | x        | Started | standard-4.0.0 | Provide Diagnostic support
instance        | 4.0.0   | x        | Started | standard-4.0.0 | Provide Instance support
jaas            | 4.0.0   | x        | Started | standard-4.0.0 | Provide JAAS support
log             | 4.0.0   | x        | Started | standard-4.0.0 | Provide Log support
package         | 4.0.0   | x        | Started | standard-4.0.0 | Package commands and mbeans
service         | 4.0.0   | x        | Started | standard-4.0.0 | Provide Service support
system          | 4.0.0   | x        | Started | standard-4.0.0 | Provide System support
kar             | 4.0.0   | x        | Started | standard-4.0.0 | Provide KAR (KARaf archive) support
ssh             | 4.0.0   | x        | Started | standard-4.0.0 | Provide a SSHd server on Karaf
management      | 4.0.0   | x        | Started | standard-4.0.0 | Provide a JMX MBeanServer and a set of MBeans in
wrap            | 0.0.0   | x        | Started | standard-4.0.0 | Wrap URL handler
----

===== `feature:install`

The `feature:install` command installs a feature.

It requires the `feature` argument. The `feature` argument is the name of the feature, or the name/version of the feature.
If only the name of the feature is provided (not the version), the latest version available will be installed.

----
karaf@root()> feature:install eventadmin
----

We can simulate an installation using `-t` or `--simulate` option: it just displays what it would do, but it doesn't do it:

----
karaf@root()> feature:install -t -v eventadmin
Adding features: eventadmin/[4.0.0,4.0.0]
No deployment change.
  Managing bundle:
    org.apache.felix.metatype / 1.0.12
----

You can specify a feature version to install:

----
karaf@root()> feature:install eventadmin/4.0.0
----

By default, the `feature:install` command is not verbose. If you want to have some details about actions performed by the `feature:install`
command, you can use the `-v` option:

----
karaf@root()> feature:install -v eventadmin
Adding features: eventadmin/[4.0.0,4.0.0]
No deployment change.
Done.
----

If a feature contains a bundle which is already installed, by default, Apache Karaf will refresh this bundle.
Sometime, this refresh can cause issue to other running applications. If you want to disable the auto-refresh of installed
bundles, you can use the `-r` option:

----
karaf@root()> feature:install -v -r eventadmin
Adding features: eventadmin/[4.0.0,4.0.0]
No deployment change.
Done.
----

You can decide to not start the bundles installed by a feature using the `-s` or `--no-auto-start` option:

----
karaf@root()> feature:install -s eventadmin
----

===== `feature:start`

By default, when you install a feature, it's automatically installed. However, you can specify the `-s` option to the `feature:install` command.

As soon as you install a feature (started or not), all packages provided by the bundles defined in the feature will be available, and can be used for
the wiring in other bundles.

When starting a feature, all bundles are started, and so, the feature also exposes the services.

===== `feature:stop`

You can also stop a feature: it means that all services provided by the feature will be stop and removed from the service registry. However, the packages
are still available for the wiring (the bundles are in resolved state).

===== `feature:uninstall`

The `feature:uninstall` command uninstalls a feature. As the `feature:install` command, the `feature:uninstall` command
requires the `feature` argument. The `feature` argument is the name of the feature, or the name/version of the feature.
If only the name of the feature is provided (not the version), the latest version available will be installed.

----
karaf@root()> feature:uninstall eventadmin
----

The features resolver is involved during feature uninstallation: transitive features installed by the uninstalled feature can be uninstalled
themselves if not used by other feature.

==== Deployer

You can "hot deploy" a features XML by dropping the file directly in the `deploy` folder.

Apache Karaf provides a features deployer.

When you drop a features XML in the deploy folder, the features deployer does:
* register the features XML as a features repository
* the features with `install` attribute set to "auto" will be automatically installed by the features deployer.

For instance, dropping the following XML in the deploy folder will automatically install feature1 and feature2, whereas
feature3 won't be installed:

----
<?xml version="1.0" encoding="UTF-8"?>
<features name="my-features" xmlns="http://karaf.apache.org/xmlns/features/v1.3.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:schemaLocation="http://karaf.apache.org/xmlns/features/v1.3.0 http://karaf.apache.org/xmlns/features/v1.3.0">

    <feature name="feature1" version="1.0" install="auto">
        ...
    </feature>

    <feature name="feature2" version="1.0" install="auto">
        ...
    </feature>

    <feature name="feature3" version="1.0">
        ...
    </feature>

</features>
----

==== JMX FeatureMBean

On the JMX layer, you have a MBean dedicated to the management of the features and features repositories: the FeatureMBean.

The FeatureMBean object name is: `org.apache.karaf:type=feature,name=*`.

===== Attributes

The FeatureMBean provides two attributes:

* `Features` is a tabular data set of all features available.
* `Repositories` is a tabular data set of all registered features repositories.

The `Repositories` attribute provides the following information:

* `Name` is the name of the features repository.
* `Uri` is the URI to the features XML for this repository.
* `Features` is a tabular data set of all features (name and version) provided by this features repository.
* `Repositories` is a tabular data set of features repositories "imported" in this features repository.

The `Features` attribute provides the following information:

* `Name` is the name of the feature.
* `Version` is the version of the feature.
* `Installed` is a boolean. If true, it means that the feature is currently installed.
* `Bundles` is a tabular data set of all bundles (bundles URL) described in the feature.
* `Configurations` is a tabular data set of all configurations described in the feature.
* `Configuration Files` is a tabular data set of all configuration files described in the feature.
* `Dependencies` is a tabular data set of all dependent features described in the feature.

===== Operations

* `addRepository(url)` adds the features repository with the `url`. The `url` can be a `name` as in the `feature:repo-add` command.
* `addRepository(url, install)` adds the features repository with the `url` and automatically installs all bundles if `install` is true. The `url` can be a `name` like in the `feature:repo-add` command.
* `removeRepository(url)` removes the features repository with the `url`. The `url` can be a `name` as in the `feature:repo-remove` command.
* `installFeature(name)` installs the feature with the `name`.
* `installFeature(name, version)` installs the feature with the `name` and `version`.
* `installFeature(name, noClean, noRefresh)` installs the feature with the `name` without cleaning the bundles in case of failure, and without refreshing already installed bundles.
* `installFeature(name, version, noClean, noRefresh) ` installs the feature with the `name` and `version` without cleaning the bundles in case of failure, and without refreshing already installed bundles.
* `uninstallFeature(name)` uninstalls the feature with the `name`.
* `uninstallFeature(name, version)` uninstalls the feature with the `name` and `version`.

===== Notifications

The FeatureMBean sends two kind of notifications (on which you can subscribe and react):

* When a feature repository changes (added or removed).
* When a feature changes (installed or uninstalled).
