Sometimes you need to test if a network connection works without actually using the intended client program. Normally you would use a tool like telnet or nc to do this, e.g. $ telnet www.google.com 80 Trying 172.217.20.68… Connected to www.google.com. Escape character is ‘^]’. or $ nc -z -v -w5 www.google.com 80 Connection to www.google.com […]
Author Archives: admin
PV Display
PV Display is an Android app to view data on the PV Output website. You can view live solar panel data and browse through historical data. The data is presented in five different tabs in both graphical and tabular form. It works in portrait mode: And in landscape mode: […]
Enable HTTPS on Jenkins
Jenkins uses HTTP by default. You can enable HTTPS by performing a couple of steps. You need to acquire an SSL certificate and corresponding key for a domain that is under your control, and tell Jenkins that it needs to use these resources. Jenkins needs a password store to be able to use your SSL […]
Enable HTTPS on Gitlab
The Gitlab self-hosted application uses HTTP by default. You can enable HTTPS by performing a couple of steps. You need to acquire an SSL certificate and corresponding key for a domain that is under your control, and tell Gitlab that it needs to use these resources. Create a directory which will hold the certificate and […]
Monitoring hosts with CollectD, InfluxDB and Grafana
In this article we will install a monitoring solution on CentOS 7 consisting of CollectD, InfluxDB and Grafana. The first step is to install CollectD: yum -y install epel-release yum -y install collectd At the time of writing, this resulted in the installation of CollectD version 5.5.0. If you are using an older version of […]
Linux network auto shutdown from APC UPS
The APC Smart-UPS series of UPS devices allows you to power servers and switches when there is a power failure in the grid. When the UPS is running on batteries, you want your servers to be notified and properly shutdown. This article shows how you can accomplish that. We use the APC Smart-UPS X2200, with […]
Serialize and deserialize a list of polymorphic objects with GSON
GSON is a great Java library for serializing and deserializing objects to and from JSON strings. When you have a list of polymorphic objects you want to serialize and deserialize, things get a bit more difficult. You have to tell GSON which type of object you expect when deserializing. When you have a list of […]
Applying Innovative IT Modelling Methods to Low-level Grid Information for DSO Operations
I presented a paper called Applying Innovative IT Modelling Methods to Low-level Grid Information for DSO Operations at the PowerTech Eindhoven 2015 conference. Distribution system operators will gather an increasing amount of electricity data from the lower level of the grid to be able to cope with several challenges, such as an increase of distributed, […]
Dynamically Scaling Apache Storm for the Analysis of Streaming Data
I presented a paper called Dynamically Scaling Apache Storm for the Analysis of Streaming Data at the 1st International Conference on Big Data Service (IEEE BigDataService 2015). Stream processing platforms allow applications to analyse incoming data continuously. Several use cases exist that make use of these capabilities, ranging from monitoring of physical infrastructures to pre selecting […]
Installing CoreOS on a XenServer VM
This guide can be used to install CoreOS on a XenServer VM. We will use PXE to boot a fresh VM, SSH into the box, run the install script, fix an issue with kexec not being available on XenServer, and rebooting into the installed CoreOS machine. We start with the creation of suitable configuration files […]