Page tree

This is an archive of the ONOS 1.1 wiki. For the current ONOS wiki, look here.

Skip to end of metadata
Go to start of metadata

Work-in-progress. Completed page will be linked into the Tutorials and Walkthroughs page.


This tutorial shows you how to incorporate tunable parameters into your component by making the link-flapping behavior of the NullLinkProvider from the Provider Tutorial configurable.

By completing this tutorial, you will understand:

  • The usage of @Property and @Modified annotations to add and use tunable parameters
  • The usage of configuration files to apply user configurations

While we use a Provider in this tutorial, the procedure described here is also applicable to applications.

As in the case of other tutorials, ${ONOS_ROOT} refers to the project root directory of ONOS, and ${KARAF_ROOT} refers to the installation location of Apache Karaf.


1. Modify the component POM file.

We use Component Contexts to pass configuration information to the component. The following should be added to the component's POM file, in this case, the Provider-specific pom.xml, in ${ONOS_ROOT}/providers/null/link :

Provider-specific pom.xml
    <!-- This is needed by ComponentContext, used for tunable configuration -->

2. Add support for configuration.

We make a few modifications to the NullLinkProvider:
// new imports
import static;

import org.osgi.service.component.ComponentContext;
import org.apache.felix.scr.annotations.Modified;
import java.util.Dictionary;

// ...<snip>...

public class NullLinkProvider extends AbstractProvider implements LinkProvider {

    private final Logger log = getLogger(getClass());   

    // The Manager serving as communication point between the ONOS core and this Provider
    @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
    protected LinkProviderRegistry providerRegistry;

    // The interface that defines how this Provider can interact with the core
    private LinkProviderService providerService;

    public NullLinkProvider() {
        // ProviderId is used by the core to identify this Provider
        // The schema "null" and FQDN of the Null southbound comprise this ID
        super(new ProviderId("null", "org.onosproject.provider.nil"));

    public void activate(ComponentContext context) {
        providerService = providerRegistry.register(this);

        // launch exactly one LinkDriver
        if (!modified(context)) {
  "Using defaults: flicker={}, eventRate={}",
                    FLICKER, DEFAULT_RATE);
            linkDriver.submit(new LinkDriver());

    public void deactivate(ComponentContext context) {
        // ...

    // The method called when configuration changes are made
    public boolean modified(ComponentContext context) {
        return false;
    // ...<snip>...

We note two features needed for configurability:

  • ComponentContext context : Used to pass around information read from a configuration file
  • @Modified : Annotation indicating that the modified() method should be called when configuration changes are made.

We call modified() from activate()so that the configuration file is read at module startup. Afterwards, the @modified annotation causes modified() to be called whenever the file is changed.

3. Annotate the tunable parameters.

The two tunable parameters for the NullLinkProvider are:

  • Enable/disable link flapping
  • Link flapping rate (in milliseconds)

Luckily, we had already defined the variables associated with these parameters, flicker and eventRate, so we annotate them (and change FLICKER to false):
// new imports
import org.apache.felix.scr.annotations.Property;

// ...<snip>...

public class NullLinkProvider extends AbstractProvider implements LinkProvider {

    // ...<snip>...

    // Default values for tunable parameters
    private static final boolean FLICKER = false;
    private static final int DEFAULT_RATE = 3000;
    @Property(name = "flicker", boolValue = FLICKER,
            label = "Setting to flap links")
    private boolean flicker = FLICKER;

    @Property(name = "eventRate", intValue = DEFAULT_RATE,
            label = "Duration between Link Event")
    private int eventRate = DEFAULT_RATE;
    // ...<snip>... 

4. Add file-parsing code.

Next, we implement modified() to parse out the values set for these parameters. - modified()
    public boolean modified(ComponentContext context) {
        // if there's no file, fall back to defaults
        if (context == null) {
  "No configs, using defaults: flicker={}, eventRate={}",
                    FLICKER, DEFAULT_RATE);
            return false;

        Dictionary<?, ?> properties = context.getProperties();
        boolean flickSetting;
        int newRate;

        // try to extract values keyed on the parameters' names
        try {
            String s = (String) properties.get("flicker");
            flickSetting = isNullOrEmpty(s) ? flicker : Boolean.valueOf(s.trim());
            s = (String) properties.get("eventRate");
            newRate = isNullOrEmpty(s) ? eventRate : Integer.valueOf(s.trim());
        } catch (Exception e) {
            flickSetting = flicker;
            newRate = eventRate;

        if (flicker != flickSetting) {
            flicker = flickSetting;

        // launch a LinkDriver with the new values, if they were changed
        if (flicker) {
            if (eventRate != newRate) {
                eventRate = newRate;
            linkDriver.submit(new LinkDriver());
  "Using settings: flicker={}, eventRate={}", flicker,
            return true;
        return false;

5. Create a configuration file.

The configurations associated with tunable components are named by the FQDN of the component. For example, the NullLinkProvider, this would be The files are added to different locations, depending on where you want to run ONOS:

  • ${ONOS_ROOT}/tools/package/etc/ , if you wan to package and deploy ONOS instances on remote machines or VMs
  • ${KARAF_ROOT}/etc/ , if you wish to launch ONOS locally on your machine

The contents of the file are simple, a list of parameter names and their values:

# Sample configurations for the NullLinkProvider.
# If enabled, generates LinkDetected and LinkVanished events
# to make the link appear to be flapping.
# flicker = true
# If enabled, sets the time between LinkEvent generation,
# in milliseconds.
# eventRate = 2000


We can now rebuild the Null Providers to test the configurability of this Provider.



  • No labels