On cloud hosting it is usually possible to connect machines with a VPN, so that it looks as if all of them were in a real physical subnet. At Amazon and Google this is called Virtual Private Cloud (VPC) and Microsoft calls it Virtual Network (VNet). Google also tells us that in their case it is implemented using Andromeda. I’m currently trying to perform these actions on a VM playground. The idea is to do a fun hobby project and to learn more about networking and Linux tooling.

Recently, I wanted to play around a bit with hosting services in VMs. Let’s imagine we want to host a service for a customer, but the service is so simple that a physical server would be overkill. Still, the server should look like a physical server to the user. For a VM to be transparent to the user, it needs to have a public IP address and should be exposed to the public internet like a real server would. If our VM would use the IP address of the host machine, we could only serve each port once and thus multiple customers would not be able to host services on the same port at the same time (except it is handled on the host in another way, e.g. by DNS name). This is of course unsatisfactory.

Today, while playing around with the zones and firewalls in my OpenWRT router, I accidentally bricked it. It would not accept any traffic from LAN anymore. It did not respond to HTTP requests, nor to SSH, nor to ping.

Es gibt wieder mal einen Überblick zu einem Modul der Fernuni Hagen von mir. Diesmal, weil das Modul “Algorithmische Geometrie” sehr umfrangreiche Themen abdeckt, meine Zeit bei der Vorbereitung aber etwas knapp war. Deshalb habe ich wieder darauf gesetzt, mit einem Blog-Eintrag einen Überblick über das gesamte Skript zu erlangen.

In this article I will show you how you can do long-term monitoring of stock prices with Grafana and get alerts when your stocks rise above or fall below a certain threshold. This can help you to keep an eye on your stocks even if you do not want to check the charts every day.