[jira] [Created] (CURATOR-457) Configuring service discovery paths

["Aleksander Melnichnikov (JIRA)" <ji...@apache.org>]

Aleksander Melnichnikov created CURATOR-457:
-----------------------------------------------

             Summary: Configuring service discovery paths
                 Key: CURATOR-457
                 URL: https://issues.apache.org/jira/browse/CURATOR-457
             Project: Apache Curator
          Issue Type: Improvement
            Reporter: Aleksander Melnichnikov
            Assignee: Jordan Zimmerman


Right now paths for services in service discovery hardcoded to pattern: */\{basePath} /\{serviceName}/\{instanceId}.* And that's impossible to configure paths this way:  */\{basePathPart1} /\{serviceName}/**

{basePathPart2}

**/\{instanceId}.* 

For example:
 If basePath = */base1/base2/base3*, serviceName = *serviceName*, instanceId - *serviceId*
 then path will be */**base1**/**base2**/**base3**/**serviceName**/**serviceId*, that can't be configured like this: */**base1**/**base2/serviceName**/**base3**/**serviceId.*

Because of strong encapsulation in ServiceDiscoveryImpl class (package private method modifiers)
{code:java}
@VisibleForTesting
String pathForName(String name) 
{ 
    return ZKPaths.makePath(basePath, name); 
}
@VisibleForTesting 
String pathForInstance(String name, String id)
{ 
   return ZKPaths.makePath(pathForName(name), id);
}
{code}
So, can we rethink visibility modifiers or add some extendable entity which would be responsible for constructing paths? 

For example:

Create interface
{code:java}
/**
 * A constructor which constructs path to services for service discovering
 */
public interface DiscoveryPathConstructor
{
    /**
     * Return the path where all service names registered
     * @return basePath
     */
    String getBasePath();

    /**
     * Return the path where all instances of service registered
     * @param name service name
     * @return path to service instances
     */
    String getPathForInstances(String name);

    /**
     * Return the path where concrete instance registered
     * @param name service name
     * @param id concrete instance id
     * @return path to concrete instance
     */
    String getPathForInstance(String name, String id);
}
{code}

And make a constructor and field in ServiceDiscoveryImpl:

{code:java}
    private final DiscoveryPathConstructor pathConstructor;
  /**
     * @param client the client
     * @param pathConstructor constructor for instances path
     * @param serializer serializer for instances (e.g. {@link JsonInstanceSerializer})
     * @param thisInstance instance that represents the service that is running. The instance will get auto-registered
     * @param watchInstances if true, watches for changes to locally registered instances
     */
    public ServiceDiscoveryImpl(CuratorFramework client, DiscoveryPathConstructor pathConstructor, InstanceSerializer<T> serializer,
                                ServiceInstance<T> thisInstance, boolean watchInstances)
    {
        this.watchInstances = watchInstances;
        this.client = Preconditions.checkNotNull(client, "client cannot be null");
        this.serializer = Preconditions.checkNotNull(serializer, "serializer cannot be null");
        this.pathConstructor = Preconditions.checkNotNull(pathConstructor, "pathConstructor cannot be null");
        if ( thisInstance != null )
        {
            Entry<T> entry = new Entry<T>(thisInstance);
            entry.cache = makeNodeCache(thisInstance);
            services.put(thisInstance.getId(), entry);
        }
    }
{code}

You can view commit in my fork of framework, if that's ok - I can make a pull request. 
https://github.com/Me1kaa/curator/commit/6e6a34db7d71a84e3a53d284fc94e1fe2e3c10d8




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