Installing Node Exporter on Linux
In OpenNMS Horizon 28+ is now a PrometheusCollector available. It scrapes the metrics from the provided exporter pages and allows to add data collections. As of speaking today it is not 100% feature complete, scraping data types like histograms is not implemented yet. If you want to play around here is a quick way to get the Linux Node_Exporter installed. The following steps are executed in a root shell with sudo -i. Continue reading
Hardening SSH for audit
Running a server in the public requires some additional work. Especially if you want management access via SSH for Ansible or if you want break stuff manually with fiddeling around :) You can run an SSH audit of your public server using https://www.sshaudit.com. This section here is a very condensed way to get an A rating. Just use strong host key for authentication of the host # file: /etc/ssh/sshd_config HostKey /etc/ssh/ssh_host_ed25519_key HostKey /etc/ssh/ssh_host_rsa_key Delete existing keys and re-generate the RSA and ED25519 keys Continue reading
UCARP and High Availability
If you have ever played with BSD you probably ran into CARP. It allows you to build a high available service which is provided by two physical servers behind a virtual shared IP address. The CARP nodes define a master and a backup system. A master serves the content and if the master crashes, the backup system takes over automatically the virtual IP (VIP) and the client won’t notice. Disclaimer: You should be aware this setup will not share load and increase your network throughput. Continue reading
Docker build and cache invalidation
Right now I’m working with my work mates @opennms integrating the docker image building in our CI/CD environment. We build our container image based on CentOS and we noticed the caching doesn’t work for ${reasons}. Running a docker build -t myimage . ended up always in installing packages from the official yum repositories even we haven’t changed anything in the Dockerfile. To understand things better, I went back to drawing board and started with a simple example and rebuilding things step by step to understand when gets the docker build cache unnecessarily invalidated. Continue reading
Docker, Java, Signals and Pid 1
Running a Java application in a container seems to be very easy. The devil is in the details and I want to shed some light on the PID 1 problem when you run Java applications in containers. In a general running applications in containers should not have any state so you just don’t care, but reality is different forces you to have to. Signals are used to a running process to behave in a certain ways. Continue reading
SSL and Java
Running applications with a current Java is not a big deal thanks Let’s Encrypt. This article describes what happens if you want to authenticate your OpenNMS against LDAP using SSL with a self-certified certificate. First of all I assume you have confiured verything so you can authenticate against LDAP in plaintext and you got a role mapping as you wanted it. If not you can have a look here. So the naive approach would be, just changing the line in your activeDirectory. Continue reading
Send notifications with Signal
In some cases it is nice to have notifications from OpenNMS in a separate channel on a smartphone and you don’t want to pay for SMS. Here is a tutorial where I use Signal using the signal-cli. This Howto will describe how to download the latest signal-cli tool, link it to your existing Signal account and how to configure OpenNMS to use it as a notification target. You should have already an OpenNMS Horizon or Meridian running and you need a Signal account with the Signal app installed and configured on your smartphone. Continue reading
Everyone can change it and why you shouldn't
Open Source software is great. If there is something you don’t like, you can at least - try to change it. A lot of Open Source software out there is not primarily used by private people. There are many companies who provide professional services around Open Source software. Some of them try to enhance the appearance with custom User Interfaces, their company logo to fit their own Corporate Identity. There are several motivations, mostly they want to be distinguished on the marked or need some easy to maintain little customization which allows their sales guys easier to sell a project and not using the software from the community projects website. Continue reading