How to Start Sling with the Kickstarter

About this How-To

What we'll explore:

  • We'll start Sling with the Kickstart Launcher (a.k.a the kickstarter) and explore the Feature Model

What you should know:

  • Skill Level: Beginner
  • Environment: Windows/Unix
  • Time: 20 minutes


In order to follow this how-to you'll need the following on your computer:

  • Java 8
  • Bash shell

What's the Kickstarter

Prior to the Kickstarter, the Sling application was assembled into an uber JAR using the Provisioning Model. The JAR file was fairly large in size and weighed in at ~70MB. If the Sling application required a new bundle, the uber JAR would have to be rebuilt. The Kickstarter was designed to solve this problem as well as streamline the application packaging process.

The Kickstarter provides a method to start Sling using a new application packaging/assembly approach known as the Feature Model. By default, the Kickstarter is configured with a minimum set of feature definitions to produce a lightweight Sling application. If additional customization is required, simply define additional features based on your requirements. Any additional features will then be pulled from a Maven repository.

How does the Kickstarter work

The Kickstarter uses the Feature Model Launcher to start a Sling instance. It sets up a control port to manage the instance and provides default values to start Sling. The Feature Launcher then downloads the necessary dependencies and installs them into the OSGi container.

Let's try this out!

Step 1: Download the Kickstarter

At the time of this writing, the latest Kickstarter version was 0.0.2. Adjust the commands below to reflect the version you downloaded.

Visit the Apache Sling Downloads page and download the Kickstart Project bundle.

Then, create a working directory for the Kickstarter and copy the bundle to this location. You can name this directory anything you like.

$ mkdir kickstarter
$ cd kickstarter
$ cp /some/download/path/ .

Step 2: Start Sling with the Kickstarter

Make sure nothing is listening on port 8080 as this port will be used by Sling.

Run the Kickstarter to start Sling.

$ java -jar

Next, open a browser and visit http://localhost:8080/.

  • The Kickstarter will take some time to start the first time since the Feature Model needs to populate your local Maven repository with any missing artifacts.
  • If you run into any issues, try re-running the Kickstarter with the -v option.

Step 3: Start using Sling

Click the Login link and log in with admin/admin.

Step 4: Check the status of Sling

Open a new terminal window and navigate to the same Kickstarter working directory that was used to start Sling.

Now, run the Kickstarter JAR again with the status command to view the current status of your Sling instance.

$ java -jar status

If your Sling instance is running, you should see output similar to this:

Sent 'status' to / OK
Terminate VM, status: 0

If your sling instance is not running, you should see:

No Apache Sling running at /
Terminate VM, status: 3

Step 5: Stop Sling with the Kickstater

Run the Kickstarter JAR again and specify the stop command.

$ java -jar stop

Alternatively, you can stop Sling by hitting <CTRL+C>.

Mission Accomplished

What we learned:

  • We successfully started Sling with the Kickstarter and had our first glimpse of the Feature Model.

Did we succeed in making you more curious about the world of Feature Models? If you stay with us, you'll learn how to customize Sling by creating your own Feature Models.

If you still want to learn a bit more about the Kickstarter, stay on this page and keep reading.

A couple additional things to explore

Kickstarter commands and options

The generalized command for the Kickstarter is as follows:

$ java -jar <jarfile> [options] [command]

It supports three commands: stop, start and status as well as a number of options. For a full list of available options, run the Kickstarter with the -h option.

Short Option Long Option Description
-a --address=<address> Address to bind to (default
-af --additionalFeature=<additionalFeature> Define additional feature files. Use multiple options for multiple features.
-c --slingHome=<slingHome> Sling context directory (default sling).
-D --define=<key=value> Sets property key to value. This is different than the -D JVM option. This must come after the jar filename.
-f --logFile=<logFile> Log file or "-" for stdout (default logs/error.log).
-h --help Display usage.
-i --launcherHome=<launcherHome> Launcher home directory (default launcher).
-j --control=<controlAddress> Host and port to use for control connection. Format [host:]port.
-l --logLevel=<logLevel> Initial log level (0..4, FATAL, ERROR, WARN, INFO, DEBUG).
-n --noShutdownHook Don't install the shutdown hook.
-p --port=<port> Port to listen to (default 8080).
-r --context=<contextPath> Root servlet context path for the HTTP service (default /).
-s --mainFeature=<mainFeatureFile> Main feature file (file path or URL). This will replace the default file used by Sling.
-v --verbose Start the launcher with additional information.

For compatibility, most of the options are the same as the Sling Starter project. The options below are specific to the Kickstarter.

  • -s: Replaces the main default Sling feature with your own Feature Model.
  • -af: Defines additional Feature Models (use multiple -af options for multiple features).

Start Sling using --mainFeature

The real power of the Kickstarter can be seen when you specify your own Feature Model. As an example, let's re-run the Kickstarter and specify an external Feature Model.

We'll start by moving into our kickstarter workspace. Then, we'll Stop Sling if it's still running. Next, remove the old conf and launcher directories so that we can start a clean Sling instance. Extract the Sling 12 Feature Model file from the Kickstarter JAR. Lastly, start Sling using the Feature Model JSON file.

$ cd kickstarter
$ java -jar stop
$ rm -rf conf launcher
$ jar -xf feature-sling12.json
$ java -jar --mainFeature=feature-sling12.json

If you're curious, take a peak at the Feature Model for Sling 12 by opening feature-sling12.json in your favorite editor.

- ( How to Start Sling with the Kickstarter )