A short presentation for a Scala Meetup. EsterTech Esper and TypeSafe Akka were discussed in the context of Complex Event Processing.

1. COMPLEX EVENT PROCESSING:
FROM ESPER BACK TO AKKA
Alexander Solovyev
solovyov.a.g@gmail.com

2. DESCRIPTION OF THE PROBLEM
Complex Event Processing: a method of tracking and analyzing event
streams to identify meaningful patterns (such as opportunities or threats)
and respond to them as quickly as possible.
Example: changing of…
• …financial parameters of the client accounts
• e.g. margin level
• …application parameters / indicators like…
• heartbeats, status of connections
• memory/CPU activity etc.

3. ABOUT THE PROJECT IN A NUTSHELL
Monitoring Service
• built on Scala and Akka
• input - a stream of asynchronous events
• HTTP as a transport
• output - an alert or alerts in case of a problem

4. BASIC TECHNICAL REQUIREMENTS
• Scala, or Java, or whatever that can run on JVM
• in-process
• open-source
Nice to have:
• declarative DSL is a plus

5. AVAILABLE OPTIONS
• TIBCO StreamBase, Oracle CEP
• commercial
• Storm
• …not mature at the moment of the choice
• but now might be considered: has a Trident DSL etc.
• Apache Camel
• more about event routing & transformation
• albeit, http://camel.apache.org/cep.html
• EsperTech Esper
• meets all the formal requirements
• has a commercial support

6. OTHER INTERESTING CANDIDATES
• Akka Streams
• Drools Fusion
• Pivotal Real-Time Intelligence for Telcos (RTI4T)
• Spark Streaming

7. ESPER
Example: absence of heartbeats.
Esper Event Processing Language, a bit simplified query:
select * from pattern [
every Event_A -> (timer:interval(10 sec) and not Event_B)]
…then write a simple Esper event listener and we are done.
Isn’t it cute? J …wish it was so…

8. Margin Level alerting
if within last T seconds margin level is above a given limit during N seconds in
sum, than raise the margin level alert.
• At least three alert levels.
• No duplicates, no false positives.
MORE COMPLEX EXAMPLE

9. ESPER PITFALLS
• EPL has a steep learning curve
• has at least two dialects
• includes quite a few different built-in “views”, functions etc.
• documentation is a reference book plus a set of samples rather than a
tutorial
• Unit-testing of actors gets more complicated (due to different groups of
threads)
An impact on development, and which is even more important, on maintenance.

10. THE ESCAPE
Why wouldn’t just use the Akka framework?
• out-of-box event handling
• very cheap state: no need to think about thread synchronization etc.
• timers to introduce notation of time
Indeed this is more verbose, but we get simplicity in lieu.
P. S. Erlang experts often choose a similar approach for tasks like being
described above – applying of the actor model.

11. A NOTE FROM TYPESAFE
There are no technical blockers to use Akka and Esper together.
An appropriate template is provided:
• http://typesafe.com/activator/template/akka-with-esper

12. THANK YOU
…and your questions J