DDevelopment & Design

TouK Nussknacker – using Apache Flink made easier for analysts and business

  • bympr
  • September 4, 2017
  • 2 minute read

Few weeks ago we (TouK) revealed on Github our latest open source project – Nussknacker. What is it and why should you care?

Why?

First, some history: more than year ago one of our clients decided it’s high time for Real Time Marketing. They had pretty large data streams and lots of ideas for marketing campaigns, so one of the key success factors was the ability to process the data fast. We prepared a POC based on Apache Flink and it turned out that it’s really great piece of technology – fast and accurate.

There was just one problem – how to write and customize processes? Flink, as many modern stream processing engines, provides rich and friendly DSL, both in Java and Scala. But for our client that was not really enough. See, they are enterprise that do not employ developers – they have many decent, competent analysts who know the business and SQL – but not Java or (Heaven forbid…) Scala.

Nussknacker to the rescue!

So we decided to create a simple process designer for them. It looks more or less like this:

You draw a diagram, fill in the details (like filter expressions – “#input.usageData > 0” or SMS/mail content), then you press the Deploy button and voilà – your brand new process in running on Flink cluster!

Of course first somebody (that is, developer) has to prepare data sources (most probably Kafka topics), design data model (POJOs or case classes) and implement actions – like sending emails or sending some events to another Kafka topic. But once a model of data and external services are defined, an analyst can define and deploy processes all by him/herself.

More features

Sounds a bit scary to let your users run stream processes with GUI? Bad filter conditions can have serious performance implications if you deal with streams of tens of thousands of events per second… That’s why we let user test their diagrams first – each test case can be generated by sample of real data coming from e.g. Kafka and then run in Flink sandbox mini-cluster.

We have also many more features that make working with Nussknacker and Flink easier: subprocesses, versioning, generating PDF documentation, migration between environments and last but certainly not least – integration with InfluxDB/Grafana to provide detailed insight into how process is doing:

Where can I use it?

What are Nussknacker use cases? Our main deployments deal with RTM (Real Time Marketing). One of our clients started with RTM and then found out that Nussknacker is also great choice for fraud detection in real time. Industries we are working with include telcos, banks and media companies. We are also thinking about other possibilities – for example IoT.

Sounds cool?

If you are interested in easy access for semi-technical analysts to streaming data – give Nussknacker a try!

You can find the code at Github: https://github.com/touk/nussknacker, we also have a nice, Docker-based quickstart: https://touk.github.io/nussknacker/Quickstart.html.

And if you are coming to Flink Forward next week in Berlin – join me on Wednesday afternoon to hear more – <a href="https://berlin.flink-forward.org/kb_sessions/touk-nussknacker-creating-flink-jobs-with-gui/"https://berlin.flink-forward.org/kb_sessions/touk-nussknacker-creating-flink-jobs-with-gui/.

In next days/weeks we’ll post more information on TouK blog both on Nussknacker architecture and internals and on interesting use cases – stay tuned :)

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Easy fraud detection in Nigerian bank with TouK Nussknacker

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DDevelopment & Design

Phonegap / Cordova and cross domain ssl request problem on android.

In one app I have participated, there was a use case:
  • User fill up a form.
  • User submit the form.
  • System send data via https to server and show a response.
During development there wasn’t any problem, but when we were going to release production version then some unsuspected situation occurred. I prepare the production version accordingly with standard flow for Android environment:
  • ant release
  • align
  • signing
During conduct tests on that version, every time I try to submit the form, a connection error appear. In that situation, at the first you should check whitelist in cordova settings. Every URL you want to connect to, must be explicit type in: 
res/xml/cordova.xml
If whitelist looks fine, the error is most likely caused by inner implementation of Android System. The Android WebView does not allow by default self-signed SSL certs. When app is debug-signed the SSL error is ignored, but if app is release-signed connection to untrusted services is blocked.



Workaround


You have to remember that secure connection to service with self-signed certificate is risky and unrecommended. But if you know what you are doing there is some workaround of the security problem. Behavior of method 
CordovaWebViewClient.onReceivedSslError
must be changed.


Thus add new class extended CordovaWebViewClient and override ‘onReceivedSslError’. I strongly suggest to implement custom onReceiveSslError as secure as possible. I know that the problem occours when app try connect to example.domain.com and in spite of self signed certificate the domain is trusted, so only for that case the SslError is ignored. 

public class MyWebViewClient extends CordovaWebViewClient {

   private static final String TAG = MyWebViewClient.class.getName();
   private static final String AVAILABLE_SLL_CN 
                               = "example.domain.com";

   public MyWebViewClient(DroidGap ctx) {
       super(ctx);
   }

   @Override
   public void onReceivedSslError(WebView view, 
                                  SslErrorHandler handler, 
                                  android.net.http.SslError error) {

       String errorSourceCName = error.getCertificate().
                                  getIssuedTo().getCName();

       if( AVAILABLE_SLL_CN.equals(errorSourceCName) ) {
           Log.i(TAG, "Detect ssl connection error: " + 
                       error.toString() + 
                       „ so the error is ignored”);

           handler.proceed();
           return;
       }

       super.onReceivedSslError(view, handler, error);
   }
}
Next step is forcing yours app to  use custom implementation of WebViewClient. 

public class Start extends DroidGap
{
   private static final String TAG = Start.class.getName();

   @Override
   public void onCreate(Bundle savedInstanceState)
   {
       super.onCreate(savedInstanceState);
       super.setIntegerProperty("splashscreen", R.drawable.splash);
       super.init();

       MyWebViewClient myWebViewClient = new MyWebViewClient(this);
       myWebViewClient.setWebView(this.appView);

       this.appView.setWebViewClient(myWebViewClient);
       
       // yours code

   }
}
That is all ypu have to do if minSdk of yours app is greater or equals 8. In older version of Android there is no class 
android.net.http.SslError
So in class MyCordovaWebViewClient class there are errors because compliator doesn’t see SslError class. Fortunately Android is(was) open source, so it is easy to find source of the class. There is no inpediments to ‘upgrade’ app and just add the file to project. I suggest to keep original packages. Thus after all operations the source tree looks like:

Class SslError placed in source tree. 
 Now the app created in release mode can connect via https to services with self-signed SSl certificates.
DDevelopment & Design

Using Eclipse snippets for faster JUnit test creation (with Mockito!)

I'm using this snippet to create a template of new unit test method supporting BDD mockito tests. This is a good example for adding static imports to a class from snippets.@${testType:newType(org.junit.Test)}public void should${testname}() { ${staticIm...I'm using this snippet to create a template of new unit test method supporting BDD mockito tests. This is a good example for adding static imports to a class from snippets.@${testType:newType(org.junit.Test)}public void should${testname}() { ${staticIm...