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Posted to commits@flink.apache.org by tr...@apache.org on 2016/04/06 14:38:41 UTC
[2/7] flink-web git commit: Add CEP blog post
http://git-wip-us.apache.org/repos/asf/flink-web/blob/ebaf2975/content/news/2016/04/06/cep-monitoring.html
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+ <h1>Introducing Complex Event Processing (CEP) with Apache Flink</h1>
+
+ <article>
+ <p>06 Apr 2016 by Till Rohrmann (<a href="https://twitter.com/stsffap">@stsffap</a>)</p>
+
+<p>With the ubiquity of sensor networks and smart devices continuously collecting more and more data, we face the challenge to analyze an ever growing stream of data in near real-time.
+Being able to react quickly to changing trends or to deliver up to date business intelligence can be a decisive factor for a company’s success or failure.
+A key problem in real time processing is the detection of event patterns in data streams.</p>
+
+<p>Complex event processing (CEP) addresses exactly this problem of matching continuously incoming events against a pattern.
+The result of a matching are usually complex events which are derived from the input events.
+In contrast to traditional DBMSs where a query is executed on stored data, CEP executes data on a stored query.
+All data which is not relevant for the query can be immediately discarded.
+The advantages of this approach are obvious, given that CEP queries are applied on a potentially infinite stream of data.
+Furthermore, inputs are processed immediately.
+Once the system has seen all events for a matching sequence, results are emitted straight away.
+This aspect effectively leads to CEP’s real time analytics capability.</p>
+
+<p>Consequently, CEP’s processing paradigm drew significant interest and found application in a wide variety of use cases.
+Most notably, CEP is used nowadays for financial applications such as stock market trend and credit card fraud detection.
+Moreover, it is used in RFID-based tracking and monitoring, for example, to detect thefts in a warehouse where items are not properly checked out.
+CEP can also be used to detect network intrusion by specifying patterns of suspicious user behaviour.</p>
+
+<p>Apache Flink with its true streaming nature and its capabilities for low latency as well as high throughput stream processing is a natural fit for CEP workloads.
+Consequently, the Flink community has introduced the first version of a new <a href="https://ci.apache.org/projects/flink/flink-docs-master/apis/streaming/libs/cep.html">CEP library</a> with <a href="http://flink.apache.org/news/2016/03/08/release-1.0.0.html">Flink 1.0</a>.
+In the remainder of this blog post, we introduce Flink’s CEP library and we illustrate its ease of use through the example of monitoring a data center.</p>
+
+<h2 id="monitoring-and-alert-generation-for-data-centers">Monitoring and alert generation for data centers</h2>
+
+<center>
+<img src="/img/blog/cep-monitoring.svg" style="width:600px;margin:15px" />
+</center>
+
+<p>Assume we have a data center with a number of racks.
+For each rack the power consumption and the temperature are monitored.
+Whenever such a measurement takes place, a new power or temperature event is generated, respectively.
+Based on this monitoring event stream, we want to detect racks that are about to overheat, and dynamically adapt their workload and cooling.</p>
+
+<p>For this scenario we use a two staged approach.
+First, we monitor the temperature events.
+Whenever we see two consecutive events whose temperature exceeds a threshold value, we generate a temperature warning with the current average temperature.
+A temperature warning does not necessarily indicate that a rack is about to overheat.
+But whenever we see two consecutive warnings with increasing temperatures, then we want to issue an alert for this rack.
+This alert can then lead to countermeasures to cool the rack.</p>
+
+<h3 id="implementation-with-apache-flink">Implementation with Apache Flink</h3>
+
+<p>First, we define the messages of the incoming monitoring event stream.
+Every monitoring message contains its originating rack ID.
+The temperature event additionally contains the current temperature and the power consumption event contains the current voltage.
+We model the events as POJOs:</p>
+
+<div class="highlight"><pre><code class="language-java"><span class="kd">public</span> <span class="kd">abstract</span> <span class="kd">class</span> <span class="nc">MonitoringEvent</span> <span class="o">{</span>
+ <span class="kd">private</span> <span class="kt">int</span> <span class="n">rackID</span><span class="o">;</span>
+ <span class="o">...</span>
+<span class="o">}</span>
+
+<span class="kd">public</span> <span class="kd">class</span> <span class="nc">TemperatureEvent</span> <span class="kd">extends</span> <span class="n">MonitoringEvent</span> <span class="o">{</span>
+ <span class="kd">private</span> <span class="kt">double</span> <span class="n">temperature</span><span class="o">;</span>
+ <span class="o">...</span>
+<span class="o">}</span>
+
+<span class="kd">public</span> <span class="kd">class</span> <span class="nc">PowerEvent</span> <span class="kd">extends</span> <span class="n">MonitoringEvent</span> <span class="o">{</span>
+ <span class="kd">private</span> <span class="kt">double</span> <span class="n">voltage</span><span class="o">;</span>
+ <span class="o">...</span>
+<span class="o">}</span></code></pre></div>
+
+<p>Now we can ingest the monitoring event stream using one of Flink’s connectors (e.g. Kafka, RabbitMQ, etc.).
+This will give us a <code>DataStream<MonitoringEvent> inputEventStream</code> which we will use as the input for Flink’s CEP operator.
+But first, we have to define the event pattern to detect temperature warnings.
+The CEP library offers an intuitive <a href="https://ci.apache.org/projects/flink/flink-docs-master/apis/streaming/libs/cep.html#the-pattern-api">Pattern API</a> to easily define these complex patterns.</p>
+
+<p>Every pattern consists of a sequence of events which can have optional filter conditions assigned.
+A pattern always starts with a first event to which we will assign the name <code>“First Event”</code>.</p>
+
+<div class="highlight"><pre><code class="language-java"><span class="n">Pattern</span><span class="o">.<</span><span class="n">MonitoringEvent</span><span class="o">></span><span class="n">begin</span><span class="o">(</span><span class="s">"First Event"</span><span class="o">);</span></code></pre></div>
+
+<p>This pattern will match every monitoring event.
+Since we are only interested in <code>TemperatureEvents</code> whose temperature is above a threshold value, we have to add an additional subtype constraint and a where clause:</p>
+
+<div class="highlight"><pre><code class="language-java"><span class="n">Pattern</span><span class="o">.<</span><span class="n">MonitoringEvent</span><span class="o">></span><span class="n">begin</span><span class="o">(</span><span class="s">"First Event"</span><span class="o">)</span>
+ <span class="o">.</span><span class="na">subtype</span><span class="o">(</span><span class="n">TemperatureEvent</span><span class="o">.</span><span class="na">class</span><span class="o">)</span>
+ <span class="o">.</span><span class="na">where</span><span class="o">(</span><span class="n">evt</span> <span class="o">-></span> <span class="n">evt</span><span class="o">.</span><span class="na">getTemperature</span><span class="o">()</span> <span class="o">>=</span> <span class="n">TEMPERATURE_THRESHOLD</span><span class="o">);</span></code></pre></div>
+
+<p>As stated before, we want to generate a <code>TemperatureWarning</code> if and only if we see two consecutive <code>TemperatureEvents</code> for the same rack whose temperatures are too high.
+The Pattern API offers the <code>next</code> call which allows us to add a new event to our pattern.
+This event has to follow directly the first matching event in order for the whole pattern to match.</p>
+
+<div class="highlight"><pre><code class="language-java"><span class="n">Pattern</span><span class="o"><</span><span class="n">MonitoringEvent</span><span class="o">,</span> <span class="o">?></span> <span class="n">warningPattern</span> <span class="o">=</span> <span class="n">Pattern</span><span class="o">.<</span><span class="n">MonitoringEvent</span><span class="o">></span><span class="n">begin</span><span class="o">(</span><span class="s">"First Event"</span><span class="o">)</span>
+ <span class="o">.</span><span class="na">subtype</span><span class="o">(</span><span class="n">TemperatureEvent</span><span class="o">.</span><span class="na">class</span><span class="o">)</span>
+ <span class="o">.</span><span class="na">where</span><span class="o">(</span><span class="n">evt</span> <span class="o">-></span> <span class="n">evt</span><span class="o">.</span><span class="na">getTemperature</span><span class="o">()</span> <span class="o">>=</span> <span class="n">TEMPERATURE_THRESHOLD</span><span class="o">)</span>
+ <span class="o">.</span><span class="na">next</span><span class="o">(</span><span class="s">"Second Event"</span><span class="o">)</span>
+ <span class="o">.</span><span class="na">subtype</span><span class="o">(</span><span class="n">TemperatureEvent</span><span class="o">.</span><span class="na">class</span><span class="o">)</span>
+ <span class="o">.</span><span class="na">where</span><span class="o">(</span><span class="n">evt</span> <span class="o">-></span> <span class="n">evt</span><span class="o">.</span><span class="na">getTemperature</span><span class="o">()</span> <span class="o">>=</span> <span class="n">TEMPERATURE_THRESHOLD</span><span class="o">)</span>
+ <span class="o">.</span><span class="na">within</span><span class="o">(</span><span class="n">Time</span><span class="o">.</span><span class="na">seconds</span><span class="o">(</span><span class="mi">10</span><span class="o">));</span></code></pre></div>
+
+<p>The final pattern definition also contains the <code>within</code> API call which defines that two consecutive <code>TemperatureEvents</code> have to occur within a time interval of 10 seconds for the pattern to match.
+Depending on the time characteristic setting, this can either be processing, ingestion or event time.</p>
+
+<p>Having defined the event pattern, we can now apply it on the <code>inputEventStream</code>.</p>
+
+<div class="highlight"><pre><code class="language-java"><span class="n">PatternStream</span><span class="o"><</span><span class="n">MonitoringEvent</span><span class="o">></span> <span class="n">tempPatternStream</span> <span class="o">=</span> <span class="n">CEP</span><span class="o">.</span><span class="na">pattern</span><span class="o">(</span>
+ <span class="n">inputEventStream</span><span class="o">.</span><span class="na">keyBy</span><span class="o">(</span><span class="s">"rackID"</span><span class="o">),</span>
+ <span class="n">warningPattern</span><span class="o">);</span></code></pre></div>
+
+<p>Since we want to generate our warnings for each rack individually, we <code>keyBy</code> the input event stream by the <code>“rackID”</code> POJO field.
+This enforces that matching events of our pattern will all have the same rack ID.</p>
+
+<p>The <code>PatternStream<MonitoringEvent></code> gives us access to successfully matched event sequences.
+They can be accessed using the <code>select</code> API call.
+The <code>select</code> API call takes a <code>PatternSelectFunction</code> which is called for every matching event sequence.
+The event sequence is provided as a <code>Map<String, MonitoringEvent></code> where each <code>MonitoringEvent</code> is identified by its assigned event name.
+Our pattern select function generates for each matching pattern a <code>TemperatureWarning</code> event.</p>
+
+<div class="highlight"><pre><code class="language-java"><span class="kd">public</span> <span class="kd">class</span> <span class="nc">TemperatureWarning</span> <span class="o">{</span>
+ <span class="kd">private</span> <span class="kt">int</span> <span class="n">rackID</span><span class="o">;</span>
+ <span class="kd">private</span> <span class="kt">double</span> <span class="n">averageTemperature</span><span class="o">;</span>
+ <span class="o">...</span>
+<span class="o">}</span>
+
+<span class="n">DataStream</span><span class="o"><</span><span class="n">TemperatureWarning</span><span class="o">></span> <span class="n">warnings</span> <span class="o">=</span> <span class="n">tempPatternStream</span><span class="o">.</span><span class="na">select</span><span class="o">(</span>
+ <span class="o">(</span><span class="n">Map</span><span class="o"><</span><span class="n">String</span><span class="o">,</span> <span class="n">MonitoringEvent</span><span class="o">></span> <span class="n">pattern</span><span class="o">)</span> <span class="o">-></span> <span class="o">{</span>
+ <span class="n">TemperatureEvent</span> <span class="n">first</span> <span class="o">=</span> <span class="o">(</span><span class="n">TemperatureEvent</span><span class="o">)</span> <span class="n">pattern</span><span class="o">.</span><span class="na">get</span><span class="o">(</span><span class="s">"First Event"</span><span class="o">);</span>
+ <span class="n">TemperatureEvent</span> <span class="n">second</span> <span class="o">=</span> <span class="o">(</span><span class="n">TemperatureEvent</span><span class="o">)</span> <span class="n">pattern</span><span class="o">.</span><span class="na">get</span><span class="o">(</span><span class="s">"Second Event"</span><span class="o">);</span>
+
+ <span class="k">return</span> <span class="k">new</span> <span class="nf">TemperatureWarning</span><span class="o">(</span>
+ <span class="n">first</span><span class="o">.</span><span class="na">getRackID</span><span class="o">(),</span>
+ <span class="o">(</span><span class="n">first</span><span class="o">.</span><span class="na">getTemperature</span><span class="o">()</span> <span class="o">+</span> <span class="n">second</span><span class="o">.</span><span class="na">getTemperature</span><span class="o">())</span> <span class="o">/</span> <span class="mi">2</span><span class="o">);</span>
+ <span class="o">}</span>
+<span class="o">);</span></code></pre></div>
+
+<p>Now we have generated a new complex event stream <code>DataStream<TemperatureWarning> warnings</code> from the initial monitoring event stream.
+This complex event stream can again be used as the input for another round of complex event processing.
+We use the <code>TemperatureWarnings</code> to generate <code>TemperatureAlerts</code> whenever we see two consecutive <code>TemperatureWarnings</code> for the same rack with increasing temperatures.
+The <code>TemperatureAlerts</code> have the following definition:</p>
+
+<div class="highlight"><pre><code class="language-java"><span class="kd">public</span> <span class="kd">class</span> <span class="nc">TemperatureAlert</span> <span class="o">{</span>
+ <span class="kd">private</span> <span class="kt">int</span> <span class="n">rackID</span><span class="o">;</span>
+ <span class="o">...</span>
+<span class="o">}</span></code></pre></div>
+
+<p>At first, we have to define our alert event pattern:</p>
+
+<div class="highlight"><pre><code class="language-java"><span class="n">Pattern</span><span class="o"><</span><span class="n">TemperatureWarning</span><span class="o">,</span> <span class="o">?></span> <span class="n">alertPattern</span> <span class="o">=</span> <span class="n">Pattern</span><span class="o">.<</span><span class="n">TemperatureWarning</span><span class="o">></span><span class="n">begin</span><span class="o">(</span><span class="s">"First Event"</span><span class="o">)</span>
+ <span class="o">.</span><span class="na">next</span><span class="o">(</span><span class="s">"Second Event"</span><span class="o">)</span>
+ <span class="o">.</span><span class="na">within</span><span class="o">(</span><span class="n">Time</span><span class="o">.</span><span class="na">seconds</span><span class="o">(</span><span class="mi">20</span><span class="o">));</span></code></pre></div>
+
+<p>This definition says that we want to see two <code>TemperatureWarnings</code> within 20 seconds.
+The first event has the name <code>“First Event”</code> and the second consecutive event has the name <code>“Second Event”</code>.
+The individual events don’t have a where clause assigned, because we need access to both events in order to decide whether the temperature is increasing.
+Therefore, we apply the filter condition in the select clause.
+But first, we obtain again a <code>PatternStream</code>.</p>
+
+<div class="highlight"><pre><code class="language-java"><span class="n">PatternStream</span><span class="o"><</span><span class="n">TemperatureWarning</span><span class="o">></span> <span class="n">alertPatternStream</span> <span class="o">=</span> <span class="n">CEP</span><span class="o">.</span><span class="na">pattern</span><span class="o">(</span>
+ <span class="n">warnings</span><span class="o">.</span><span class="na">keyBy</span><span class="o">(</span><span class="s">"rackID"</span><span class="o">),</span>
+ <span class="n">alertPattern</span><span class="o">);</span></code></pre></div>
+
+<p>Again, we <code>keyBy</code> the warnings input stream by the <code>"rackID"</code> so that we generate our alerts for each rack individually.
+Next we apply the <code>flatSelect</code> method which will give us access to matching event sequences and allows us to output an arbitrary number of complex events.
+Thus, we will only generate a <code>TemperatureAlert</code> if and only if the temperature is increasing.</p>
+
+<div class="highlight"><pre><code class="language-java"><span class="n">DataStream</span><span class="o"><</span><span class="n">TemperatureAlert</span><span class="o">></span> <span class="n">alerts</span> <span class="o">=</span> <span class="n">alertPatternStream</span><span class="o">.</span><span class="na">flatSelect</span><span class="o">(</span>
+ <span class="o">(</span><span class="n">Map</span><span class="o"><</span><span class="n">String</span><span class="o">,</span> <span class="n">TemperatureWarning</span><span class="o">></span> <span class="n">pattern</span><span class="o">,</span> <span class="n">Collector</span><span class="o"><</span><span class="n">TemperatureAlert</span><span class="o">></span> <span class="n">out</span><span class="o">)</span> <span class="o">-></span> <span class="o">{</span>
+ <span class="n">TemperatureWarning</span> <span class="n">first</span> <span class="o">=</span> <span class="n">pattern</span><span class="o">.</span><span class="na">get</span><span class="o">(</span><span class="s">"First Event"</span><span class="o">);</span>
+ <span class="n">TemperatureWarning</span> <span class="n">second</span> <span class="o">=</span> <span class="n">pattern</span><span class="o">.</span><span class="na">get</span><span class="o">(</span><span class="s">"Second Event"</span><span class="o">);</span>
+
+ <span class="k">if</span> <span class="o">(</span><span class="n">first</span><span class="o">.</span><span class="na">getAverageTemperature</span><span class="o">()</span> <span class="o"><</span> <span class="n">second</span><span class="o">.</span><span class="na">getAverageTemperature</span><span class="o">())</span> <span class="o">{</span>
+ <span class="n">out</span><span class="o">.</span><span class="na">collect</span><span class="o">(</span><span class="k">new</span> <span class="nf">TemperatureAlert</span><span class="o">(</span><span class="n">first</span><span class="o">.</span><span class="na">getRackID</span><span class="o">()));</span>
+ <span class="o">}</span>
+ <span class="o">});</span></code></pre></div>
+
+<p>The <code>DataStream<TemperatureAlert> alerts</code> is the data stream of temperature alerts for each rack.
+Based on these alerts we can now adapt the workload or cooling for overheating racks.</p>
+
+<p>The full source code for the presented example as well as an example data source which generates randomly monitoring events can be found in <a href="https://github.com/tillrohrmann/cep-monitoring">this repository</a>.</p>
+
+<h2 id="conclusion">Conclusion</h2>
+
+<p>In this blog post we have seen how easy it is to reason about event streams using Flink’s CEP library.
+Using the example of monitoring and alert generation for a data center, we have implemented a short program which notifies us when a rack is about to overheat and potentially to fail.</p>
+
+<p>In the future, the Flink community will further extend the CEP library’s functionality and expressiveness.
+Next on the road map is support for a regular expression-like pattern specification, including Kleene star, lower and upper bounds, and negation.
+Furthermore, it is planned to allow the where-clause to access fields of previously matched events.
+This feature will allow to prune unpromising event sequences early.</p>
+
+
+ </article>
+ </div>
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http://git-wip-us.apache.org/repos/asf/flink-web/blob/ebaf2975/content/slides.html
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