In this article, I will share my experience with Cassandra and how you can manage big data in an effective way. Apache Cassandra is a high-performance, extremely scalable, fault-tolerant (i.e., no single point of failure), distributed non-relational database solution. But Cassandra differs from SQL and RDBMS in some important aspects. If, like me, you come from the world of SQL databases, it’s hard to understand Cassandra’s data concept. It took me several weeks to do so. So let’s see what is the difference. Continue reading “Manage Big Data With Apache Cassandra”
EJB Transaction Timeout in Wildfly
If you have long running transactions, in Wildfly it can happen that you run into a timeout durinng your processing EJB method. In this case you can change the default timeout from 5 minutes via the standalone.xml file:
<subsystem xmlns="urn:jboss:domain:transactions:4.0"> <core-environment> <process-id> <uuid/> </process-id> </core-environment> <recovery-environment socket-binding="txn-recovery-environment" status-socket-binding="txn-status-manager"/> <coordinator-environment default-timeout="1200"/> <object-store path="tx-object-store" relative-to="jboss.server.data.dir"/> </subsystem>
In this example I changed the coordinator-environment default-timeout to 20 minutes
An Alternative to Kubernetes
Kubernetes is an container-orchestration system which helps you to automate your deployment, scaling and management of containerized applications. Originally this platform was designed by Google and is today part of the Cloud Native Computing Foundation. Kubernetes is surely one of the major providers in the market of container operating systems.
But what many do not know, is the complexity of this platform if used in smaller projects. To understand this you need to know, that Kubernetes was designed for the operation of large cloud environments as they are operated by Google, Amazon or Microsoft. This means that with the help of Kubernetes you can not only manage one server, but hundreds of servers with thousands of services. For most projects, this power is superfluous. Continue reading “An Alternative to Kubernetes”
WWW Inventor Tim Berners-Lee Launches a Project to Save the Internet
The WWW Inventor Tim Berners-Lee Launches a new open platform called “Solid”. With Solid, users can share their data with others without having to surrender their sovereignty to a group. Users should be able to decide for themselves who can access the data and which apps will be used.
To solve the problem of how to control personal data, in Solid all data is stored in a so called Solid POD. This Solid POD can be in your house or workplace, or with an online Solid POD provider of your choice. Since you control your server you own your data. You’re free to move it at any time, without interruption of service.
In my opinion, this is the only sensible solution to return data control back to the user. I hope this project gets enough attention. Your data is too serious to ignore.
Use Docker Instead of Kubernetes
Today we are all talking about Containers and container based infrastructure. There is a lot of hype and noise about this topic. But what is this container technology? And how does it solve today problems?
I am using containers by myself and of course I am fascinated from this server technology. Containers can really simplify things. After more than 20 years in building server applications I have experienced many problems very closely.
I call it “server technology“, which may sound a little strange to some. Are containers not more of a cloud technology? And this is the one thing that really bothers me is this current hype. When I talk about containers many people think about this Kubernetes thing. And this was the impulse to write this article. Continue reading “Use Docker Instead of Kubernetes”
Docker Container Persistence
Today I found a very good article on DZone.com about how to manage persistence for statefull docker containers. The article is from StorageOS and gives a very good overview about the problems and requirements.
Read the full article here: https://dzone.com/refcardz/persistent-container-storage?chapter=1
XSLT 2.0 with Eclipse and Wildfly
Eclipse IDE provides a cool feature which allows you to execute XSL templates within the IDE. You just need to select the XSL file together with the XML file and choose from the context menu
Run As -> XSL Transformation
But for some reasons Eclipse is not supporting XSL 2.0 – which is standard in these days. So for example if you try to use xsl functions like ‘format-date-time’ or ‘replace’ this will not work. This is also true for Wilfly application server. So here is how to add XSLT 2.0 support for both – Eclipse and Wilffly
Eclipse IDE
You can install an XSLT 2.0 processor manually into your Eclipse IDE:
- Download the latest Saxon XSLT processor
- Unzip the package to get the saxon9he.jar file and place it into your workspace or some external folder
- In eclipse choose “Window > Preferences” then “XML > XSL > Java Processors > Add”
- Fill in a “Processor Name”, e.g. “Saxon XSLT 2.0”
- In field “Processor type” choose “Saxon (XSLT 2.0)”
- Choose “Add external jar” and choose your saxon jar, e.g. “saxon9he.jar”
- Confirm by clicking “OK”
Now you can use saxon for XSLT 2.0 transformations in Eclipse. You need just configure your Run As Configurations and select the option ‘use specific process‘ to select the newly added Saxon processor.
Wildfly Sever
Also wildfly server supports only XSL 1.0 per default. If you need XSL 2.0 in your application add the following maven dependency:
<!-- XSL 2.0 support-->
<dependency>
<groupId>net.sf.saxon</groupId>
<artifactId>Saxon-HE</artifactId>
<version>9.8.0-14</version>
</dependency>docker-compose Fails After Network Is Removed
Today I run into a strange problem concerning docker-compose. I have several stacks defined in my developer environment. For some reason I removed old networks with the command
docker network prune
After that I was no longer able to start my aplications with docker-compose up:
docker-compose up
Creating network "myapp_default" with the default driver
Starting myapp_app_1 …
Starting myapp-db_1 … error
ERROR: for myapp-db_1 Cannot start service myapp-db: network 656be42244ac96cd35bf7fb786
The problem was that docker-compose created a new default network, but this was not defined for the already existing containers. Containers always connect to networks using the network ID which is guaranteed to be unique. And this ID was now no longer valid.
One solution is to remove all existing containers maunally. A better solution is to shut down the conainers with the command
$ docker-compose down
This will remove the internal Network IDs and you can restart the containers again with
$ docker-compose up
An Alternative for the Google App Postman….
Until today I worked with the Rest-API Testing Tool Postman from Google. But this tool was making me more and more suspicious in the last time. For example, you are recently asked to sign in with a Google account. So it was time to lookout for an alternative. And finally I found Insomnia. It is open source and hosted on Github.
To install the tool on Linux/Debian run:
# Add to sources echo "deb https://dl.bintray.com/getinsomnia/Insomnia /" \ | sudo tee -a /etc/apt/sources.list.d/insomnia.list # Add public key used to verify code signature wget --quiet -O - https://insomnia.rest/keys/debian-public.key.asc \ | sudo apt-key add - # Refresh repository sources and install Insomnia sudo apt-get update sudo apt-get install insomnia
Maven on Debian failed with JDK 1.9 – ClassFormatError
Today I ran into a problem with Maven under Debian GNU/Linux 9 (stretch). My Debian has OpenJDK 8 as also OpenJDK 9 installed. OpenJDK 9 is my default java version. My Maven version is 3.3.9.
mvn -version Apache Maven 3.3.9 Maven home: /usr/share/maven Java version: 9-Debian, vendor: Oracle Corporation Java home: /usr/lib/jvm/java-9-openjdk-amd64 Default locale: de_DE, platform encoding: UTF-8 OS name: "linux", version: "4.9.0-6-amd64", arch: "amd64", family: "unix"
The problem is, that building one of my projects results in the following ClassFormat Error:
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-surefire-plugin:2.17:test (default-test) on project imixs-workflow-core: Execution default-test of goal org.apache.maven.plugins:maven-surefire-plugin:2.17:test failed: There was an error in the forked process [ERROR] java.lang.ClassFormatError: Absent Code attribute in method that is not native or abstract in class file javax/xml/bind/JAXBException [ERROR] at java.base/java.lang.ClassLoader.defineClass1(Native Method) [ERROR] at java.base/java.lang.ClassLoader.defineClass(ClassLoader.java:1007) [ERROR] at java.base/java.security.SecureClassLoader.defineClass(SecureClassLoader.java:174) [ERROR] at java.base/jdk.internal.loader.BuiltinClassLoader.defineClass(BuiltinClassLoader.java:801) [ERROR] at java.base/jdk.internal.loader.BuiltinClassLoader.findClassOnClassPathOrNull(BuiltinClassLoader.java:699) [ERROR] at java.base/jdk.internal.loader.BuiltinClassLoader.loadClassOrNull(BuiltinClassLoader.java:622) [ERROR] at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:580) [ERROR] at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:185) [ERROR] at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:496) [ERROR] at java.base/java.lang.Class.getDeclaredMethods0(Native Method) [ERROR] at java.base/java.lang.Class.privateGetDeclaredMethods(Class.java:3139) [ERROR] at java.base/java.lang.Class.getMethodsRecursive(Class.java:3280) [ERROR] at java.base/java.lang.Class.getMethod0(Class.java:3266) [ERROR] at java.base/java.lang.Class.getMethod(Class.java:2063) [ERROR] at org.apache.maven.surefire.util.ReflectionUtils.tryGetMethod(ReflectionUtils.java:57) [ERROR] at org.apache.maven.surefire.common.junit3.JUnit3TestChecker.isSuiteOnly(JUnit3TestChecker.java:64) [ERROR] at org.apache.maven.surefire.common.junit3.JUnit3TestChecker.isValidJUnit3Test(JUnit3TestChecker.java:59) [ERROR] at org.apache.maven.surefire.common.junit3.JUnit3TestChecker.accept(JUnit3TestChecker.java:54) [ERROR] at org.apache.maven.surefire.common.junit4.JUnit4TestChecker.accept(JUnit4TestChecker.java:52) [ERROR] at org.apache.maven.surefire.util.DefaultScanResult.applyFilter(DefaultScanResult.java:97) [ERROR] at org.apache.maven.surefire.junit4.JUnit4Provider.scanClassPath(JUnit4Provider.java:206) [ERROR] at org.apache.maven.surefire.junit4.JUnit4Provider.invoke(JUnit4Provider.java:103) [ERROR] at org.apache.maven.surefire.booter.ForkedBooter.invokeProviderInSameClassLoader(ForkedBooter.java:200) [ERROR] at org.apache.maven.surefire.booter.ForkedBooter.runSuitesInProcess(ForkedBooter.java:153) [ERROR] at org.apache.maven.surefire.booter.ForkedBooter.main(ForkedBooter.java:103) [ERROR] -> [Help 1]
The problem is a incompatibility of maven 3.3.9 with JDK 1.9. To solve this problem I switch to my OpenJDK 8 by setting the JAVA_HOME variable explicitly to JDK8 :
export JAVA_HOME=/usr/lib/jvm/java-8-openjdk-amd64/
After this change maven install works fine again in my projects.
To make the JAVA_HOME setting permanent follow this stepts.
1. find your preferred java version
ls -la /usr/lib/jvm/
2. edit the file /etc/profile and add the following line with the path to the JDK 8 you find before:
export JAVA_HOME="path to jdk8 that you found"
3. verify you maven installation
mvn -version
You maven should now be set to JDK8.
I hope this post will become obsolete in near future.