Author Archives: Jan Sipke

Installing a Storm cluster on CentOS hosts

Storm is a distributed, realtime computation system to reliably process unbounded streams of data. The following picture shows how data is processed in Storm: This tutorial will show you how to install Storm on a cluster of CentOS hosts. A … Continue reading

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Installing Apache Libcloud on CentOS

Apache Libcloud is a standard Python library that abstracts away differences among multiple cloud provider APIs. At the moment it can be used to manage four different kinds of cloud services: servers, storage, loadbalancers and DNS. Here are the steps … Continue reading

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Creating a Java WebStart (JNLP) application

Java WebStart, also called Java Network Launching Protocol (JNLP), allows you to launch Java applications directly from the internet using a webbrowser. In this article we will create a simple application and all configuration files necessary to launch it through … Continue reading

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Creating network diagrams with D3.js

D3.js is a JavaScript library for manipulating documents based on data. It can be used for all sorts of visualizations including network diagrams. In this article we will create a network diagram with nodes and directed links between them, visualized … Continue reading

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Grep lines before and after matched line

The command grep is really useful for finding matches of a certain word in files or streams. However, until recently I didn’t know how to display lines before and after the matched line(s). Let’s say we have a file named … Continue reading

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Temperature graphs

In a previous article we looked at remote measurement of temperature and humidity. Now it is time to show the results of the temperature measurements. First a recap of the setup: Three remote temperature and humidity sensors are located in … Continue reading

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Measuring temperature and humidity with a JeeNode

In a previous article we looked at the Arduino. Now we will look at an (almost) Arduino compatible clone, the JeeNode. It is a bit smaller and cheaper than the original version and operates at 3.3V instead of 5V. This … Continue reading

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Programming the Arduino ethernet shield

The Arduino is an open-source electronics prototyping platform based on flexible, easy-to-use hardware and software. It features an IDE that allows you to program the Arduino using a standard USB cable. Several shields exist that extend the functionality of the … Continue reading

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Model View Controller (MVC) with JSP and JSTL

In this article we will create a small web application that uses the Model View Controller (MVC) pattern with Java Server Pages (JSP) and JSP Standard Template Library (JSTL). A container like Tomcat is needed to run this combination. Thanks … Continue reading

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Changing CPU and memory settings on XenServer VMs

You can change the CPU and memory settings of XenServer virtual machines using the API. XenServer allows you to set the priority of the virtual machine CPU (called weight), set a limit on the amount of CPU the virtual machine … Continue reading

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