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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DDevelopment & Design

Using WsLite in practice

TL;DR

There is a example working GitHub project which covers unit testing and request/response logging when using WsLite.

Why Groovy WsLite ?

I’m a huge fan of Groovy WsLite project for calling SOAP web services. Yes, in a real world you have to deal with those - big companies have huge amount of “legacy” code and are crazy about homogeneous architecture - only SOAP, Java, Oracle, AIX…

But I also never been comfortable with XFire/CXF approach of web service client code generation. I wrote a bit about other posibilites in this post. With JAXB you can also experience some freaky classloading errors - as Tomek described on his blog. In a large commercial project the “the less code the better” principle is significant. And the code generated from XSD could look kinda ugly - especially more complicated structures like sequences, choices, anys etc.

Using WsLite with native Groovy concepts like XmlSlurper could be a great choice. But since it’s a dynamic approach you have to be really careful - write good unit tests and log requests. Below are my few hints for using WsLite in practice.

Unit testing

Suppose you have some invocation of WsLite SOAPClient (original WsLite example):

def getMothersDay(long _year) {
    def response = client.send(SOAPAction: action) {
       body {
           GetMothersDay('xmlns':'http://www.27seconds.com/Holidays/US/Dates/') {
              year(_year)
           }
       }
    }
    response.GetMothersDayResponse.GetMothersDayResult.text()
}

How can the unit test like? My suggestion is to mock SOAPClient and write a simple helper to test that builded XML is correct. Example using great SpockFramework: 

void setup() {
   client = Mock(SOAPClient)
   service.client = client
}

def "should pass year to GetMothersDay and return date"() {
  given:
      def year = 2013
  when:
      def date = service.getMothersDay(year)
  then:
      1 * client.send(_, _) >> { Map params, Closure requestBuilder ->
            Document doc = buildAndParseXml(requestBuilder)
            assertXpathEvaluatesTo("$year", '//ns:GetMothersDay/ns:year', doc)
            return mockResponse(Responses.mothersDay)
      }
      date == "2013-05-12T00:00:00"
}

This uses a real cool feature of Spock - even when you mock the invocation with “any mark” (_), you are able to get actual arguments. So we can build XML that would be passed to SOAPClient's send method and check that specific XPaths are correct:

void setup() {
    engine = XMLUnit.newXpathEngine()
    engine.setNamespaceContext(new SimpleNamespaceContext(namespaces()))
}

protected Document buildAndParseXml(Closure xmlBuilder) {
    def writer = new StringWriter()
    def builder = new MarkupBuilder(writer)
    builder.xml(xmlBuilder)
    return XMLUnit.buildControlDocument(writer.toString())
}

protected void assertXpathEvaluatesTo(String expectedValue,
                                      String xpathExpression, Document doc) throws XpathException {
    Assert.assertEquals(expectedValue,
            engine.evaluate(xpathExpression, doc))
}

protected Map namespaces() {
    return [ns: 'http://www.27seconds.com/Holidays/US/Dates/']
}

The XMLUnit library is used just for XpathEngine, but it is much more powerful for comparing XML documents. The NamespaceContext is needed to use correct prefixes (e.g. ns:GetMothersDay) in your Xpath expressions.

Finally - the mock returns SOAPResponse instance filled with envelope parsed from some constant XML:

protected SOAPResponse mockResponse(String resp) {
    def envelope = new XmlSlurper().parseText(resp)
    new SOAPResponse(envelope: envelope)
}

Request and response logging

The WsLite itself doesn’t use any logging framework. We usually handle it by adding own sendWithLogging method:

private SOAPResponse sendWithLogging(String action, Closure cl) {
    SOAPResponse response = client.send(SOAPAction: action, cl)
    log(response?.httpRequest, response?.httpResponse)
    return response
}

private void log(HTTPRequest request, HTTPResponse response) {
    log.debug("HTTPRequest $request with content:\n${request?.contentAsString}")
    log.debug("HTTPResponse $response with content:\n${response?.contentAsString}")
}

This logs the actual request and response send through SOAPClient. But it logs only when invocation is successful and errors are much more interesting… So here goes withExceptionHandler method:

private SOAPResponse withExceptionHandler(Closure cl) {
    try {
        cl.call()
    } catch (SOAPFaultException soapEx) {
        log(soapEx.httpRequest, soapEx.httpResponse)
        def message = soapEx.hasFault() ? soapEx.fault.text() : soapEx.message
        throw new InfrastructureException(message)
    } catch (HTTPClientException httpEx) {
        log(httpEx.request, httpEx.response)
        throw new InfrastructureException(httpEx.message)
    }
}
def send(String action, Closure cl) {
    withExceptionHandler {
        sendWithLogging(action, cl)
    }
}

XmlSlurper gotchas

Working with XML document with XmlSlurper is generally great fun, but is some cases could introduce some problems. A trivial example is parsing an id with a number to Long value:

def id = Long.valueOf(edit.'@id' as String)

The Attribute class (which edit.'@id' evaluates to) can be converted to String using as operator, but converting to Long requires using valueOf.

The second example is a bit more complicated. Consider following XML fragment:

<edit id="3">
   <params>
      <param value="label1" name="label"/>
      <param value="2" name="param2"/>
   </params>
   <value>123</value>
</edit>
<edit id="6">
   <params>
      <param value="label2" name="label"/>
      <param value="2" name="param2"/>
   </params>
   <value>456</value>
</edit>

We want to find id of edit whose label is label1. The simplest solution seems to be:

def param = doc.edit.params.param.find { it['@value'] == 'label1' }
def edit = params.parent().parent()

But it doesn’t work! The parent method returns multiple edits, not only the one that is parent of given param…

Here’s the correct solution:

doc.edit.find { edit ->
    edit.params.param.find { it['@value'] == 'label1' }
}

Example

The example working project covering those hints could be found on GitHub.