Introduction

While working on a project for one of our customers I had to perform some testing that involved one of the WSO2 product family members, namely the Complex Event Processor (or CEP for short). While I already tested some of their products a while ago, I always did that on a Windows platform (for ease and personal preferences). But this time I had to integrate it with Graylog2 which was better run on a Linux environment anyway – and this came nicely packaged via a docker image! So I spinned up a shiny new CentOS 7 installation where running graylog was just a yum install -y docker and docker pull graylog2/allinone away … For WSO2 CEP installation things looked worse; the publisher only provided a ZIP download which I would have to extract to run the product. So I thought I’d go the extra mile and create a Dockerfile so I could run both applications nicely in parallel.

As I have never used docker before, I went quickly through their Tutorial and User Guide and gave it a try:

Step by step

1. I started of with a plain CentOS image by running docker pull centos and interactively running it docker run -i centos /bin/bash in order to test my modifications.

2. While I could download the required Oracle JDK or JRE 1.7 automatically, downloading the actual CEP product from WSO2 was not possible without interactively submitting some personal information before being redirected to the actual download link. So had to manually download it in advance and placed the ZIP into a subdirectory src (below the Dockerfile).

   1. Oracle JRE 1.7 was downloaded via wget (with the header option --header "Cookie: oraclelicense=accept-securebackup-cookie" to suppress the EULA confirmation dialogue) and extracted into /opt/jre-7-linux-x64 with a link to /opt/java. Export of JAVA_HOME and expansion of PATH was done in the recommended way via ENV (and interactively via export to be able to test the installation right away).

   2. As mentioned before downloading the actual CEP product was quite difficult to download automatically so I added it into the build process via the COPY src/wso2cep-3.1.0.zip /opt/src/wso2cep-3.1.0.zip command.

   3. After unzipping it via unzip -q /opt/src/wso2cep-3.1.0.zip -d /opt the only thing left was to test the installation by running /opt/wso2cep-3.1.0/bin/wso2server.sh (which would later become the CMD of the Dockerfile).

3. I then committed the changes to an intermediate image via docker commit abcd wso2cep-3.1.0 so I could test them prior to build. This step is optional. You can also just build the image and test it directly.

4. The actual Dockerfile for the build process was the only very short, consisting only of a few commands (mainly specifying the base image and setting the startup command): docker build -t wso2cep-3.1.0 .

   # Dockerfile to build WSO2 Complex Event Processor
   #
   # Copyright 2014 Ronald Rink, d-fens GmbH
   #
   # Licensed under the Apache License, Version 2.0 (the "License");
   # you may not use this file except in compliance with the License.
   # You may obtain a copy of the License at
   #
   # http://www.apache.org/licenses/LICENSE-2.0
   #
   # Build the container
   #       cd <path to Dockerfile>
   #       sudo docker build -t wso2cep-3.1.0 .
   #
   # Run a container using the built image
   #       sudo docker run -d -i -p 9443:9443 -t --name cep wso2cep-3.1.0
   #
   # Login to the running container
   #       sudo docker attach cep
   #
   # Exit from a attached container
   #       ^p^q (Ctrl+p and Ctrl+q)
   #
   
   # Use CentOS base image
   FROM centos
   
   # Maintainer
   MAINTAINER Ronald Rink <ronald.rink@d-fens.net>
   
   # Update system
   RUN yum update -y
   RUN yum install -y wget
   RUN yum install -y unzip
   RUN yum install -y tar
   
   ## Download and install Oracle JAVA JRE 1.7
   RUN cd /opt && wget -q --no-check-certificate --no-cookies --header "Cookie: oraclelicense=accept-securebackup-cookie" http://download.oracle.com/otn-pub/java/jdk/7/jre-7-linux-x64.tar.gz
   RUN cd /opt && tar -zxvf /opt/jre-7-linux-x64.tar.gz
   RUN rm /opt/jre-7-linux-x64.tar.gz
   RUN ln -s /opt/jre1.7.0 /opt/java
   ENV JAVA_HOME /opt/java
   ENV PATH ${PATH}:${JAVA_HOME}/bin
   
   # Install WSO2 CEP 3.1.0 (manually download it in advance and place it into a 'src' subdirectory below the 'Dockerfile')
   COPY src/wso2cep-3.1.0.zip /opt/src/wso2cep-3.1.0.zip
   RUN unzip -q /opt/src/wso2cep-3.1.0.zip -d /opt
   RUN rm /opt/src/wso2cep-3.1.0.zip
   
   # Set environment variables
   # HOME is already set correctly in centos image
   # ENV HOME /root
   
   WORKDIR /root
   
   CMD /opt/wso2cep-3.1.0/bin/wso2server.sh
   

5. After the build completed I tagged the image to include my username via docker tag wso2cep-3.1.0:latest dfch/wso2cep-3.1.0:latest …

6. … and pushed it to as a new repository dfch/wso2cep-3.1.0 with docker push dfch/wso2cep-3.1.0.
   Note: you have to first perform a docker login to be able to push the image. Caution: the passphrase is saved on the machine where you push. So be careful where you do that!

7. After running the image via docker run -d -t -i -p 9443:9443 --name cep dfch/wso2cep-3.1.0 I could launch a browser and login to the application:

Summary

• After a quick ramp up it was actually quite easy to build a docker image for the application. I am still not convinced if it is still better to integrate the binary into the image or to load it separately at start up time (which proved quite hard in in this case).

• Also I am not quite sure how ‘good’ versioning and maintenance can be applied to this image. Maybe it is best to build the complete application from source and not to use the ZIP download at all.

• You can use download the image from via docker pull dfch/wso2cep-3.1.0 and you can grab the Dockerfile from our GitHub account.

• As this is my first docker attempt (with a 4 hours learning head start), suggestions for improvement are very welcome!

UPDATE 2014-12-24 I also pushed some more images containing:

• WSO2 API Manager

• WSO2 Message Broker

• WSO2 Business Activity Monitor

• WSO2 Business Rules Server

Note

• When you run the image and assign it a name (as in the above example) you have to delete the container to be able to start it a second time (or you omit the --name option).

• The intermediate image wso2cep-3.1.0 can be deleted after the build process completes.

• Restarting the server takes quite some time

• If you want to expose more ports (like http or jms) you have to specify this in the docker run command separately.

• ‘Burning’ the application into the image certainly increases the file size considerably but also speeds up the start up time.

• Signing up to docker was very easy (as I already had a GitHub account).

• There is no docker cp equivalent for copying data from the host to the container, so using docker run -v host-path:container-path seems to be the easiest workaround.

• Not applying yum update -y will reduce the final image size by approx 150MB

• The dockerfile could be based on dockerfile / java so that an update to the java machine could be applied automatically (and to be able to choose between java versions, plus saving some space)