OpenEBS: Create persistent storage in your Charmed Kubernetes cluster

I previously wrote a blog about using StorageOS as persistent storage solution for Kubernetes here. StorageOS is dependent on etcd. I was having difficulties getting etcd up again after a reboot. Since I wanted to get a storage solution working quickly and not focus too much on external dependencies so I decided to give OpenEBS a try. In this blog I'll describe a developer installation on Charmed Kubernetes (the environment described here). I used openebs-jiva-default as storage class. This is unsuitable for production scenario's. OpenEBS also provides cStor. Most of the development effort goes there. cStor however requires a mounted block device. I have not tried this yet in my environment.

StorageOS: Create persistent storage in your Charmed Kubernetes cluster

If you want to experiment with a multi node Kubernetes cluster locally as a developer, you need a distributed persistent storage solution to approximate real production scenario's. StorageOS is one of those solutions. In this blog I describe a developer installation StorageOS. For production scenario's check out the best practices mentioned on the StorageOS site.

Charmed Kubernetes on KVM using MAAS and juju

Coming to this solution was a journey. I was looking for a Kubernetes installation which was easy to deploy and cleanup on my own laptop (I didn't want to have to pay for a hosted solution). I did want a solution which was more or less production like because I wanted to be able to play with storage solutions and deal with cluster challenges / loadbalancers. Things I couldn't do easily on environments like Minikube and Microk8s. Also, since I was running on a single piece of hardware, I needed a virtualization technology. Each one of them comes with their own challenges. On some of them it is difficult to get storage solutions to work, for example LXC/LXD (an alternative to Docker). Some of them come with networking challenges like Hyper-V and some of them just don't perform well like VirtualBox. I also needed a solution to provide some form of automation to create/destroy/access my virtual environments. A long list of requirements and this is what I ended up with. A production-like environment which is quick to create, destroy or reset, running on my laptop with easy management tools.

Quick and easy: A multi-node Kubernetes cluster on CentOS 7 + QEMU/KVM (libvirt)

Kubernetes is a popular container orchestration platform. As a developer understanding the environment in which your application is going to run is important since this can help you use available services of the platform and fix issues.

There are several options to run Kubernetes locally to get some experience with Kubernetes as developer. For example Minikube, MicroK8s and MiniShift. These options however are not representative for a real environment. They for example usually do not have master and slave nodes. Running locally requires quite different configuration compared to running multiple nodes in VMs. Think for example about how to deal with storage and a container registry which you want to share over the different nodes. Installing a full blown environment requires a lot of work and resources. Using a cloud service usually is not free and you usually have less to no control over the environment Kubernetes is running in.

In this blog I'll describe a 'middle way'. Get an easy to manage small multi node Kubernetes environment running in different VMs. You can use this environment for example to learn what the challenges of clusters are and how to deal with them efficiently.

It uses the work done here with some minor additions to get a dashboard ready.

Spring: Blocking vs non-blocking: R2DBC vs JDBC and WebFlux vs Web MVC

Spring Framework version 5, released in Sept 2017, introduced Spring WebFlux. A fully reactive stack. In Dec 2019 Spring Data R2DBC, a reactive relational database driver was released. In this blog post I'll show that at high concurrency, WebFlux and R2DBC perform better. They have better response times and higher throughput. As additional benefits, they use less memory and CPU per request processed and when leaving out JPA in case of R2DBC, your fat JAR becomes a lot smaller. At high concurrency using WebFlux and R2DBC is a good idea!

The size of Docker images containing OpenJDK 11.0.6

When running Java applications in containers, you need to be careful with your resources. If you're not careful with layering your images (for example using Google's Jib), you can quickly get into disk-space issues, especially when your base image and/or application gets updated regularly. One of the ways you can save resources is by using small base images. In this blog post I determined the uncompressed size of several base images containing OpenJDK 11.0.6 which are available on Docker Hub.

Secure browsing using a local SOCKS proxy server (on desktop or mobile) and an always free OCI compute instance as SSH server

Oracle provides several services as 'always free'. In contrast to Azure and Amazon, these include compute instances which remain 'forever' free to use. Although there are some limitations on CPU, disk, network resources, these instances are ideal to use as a remote SSH server and with a little effort a connection target for a locally running SOCKS proxy server. When you configure a browser to use that SOCKS proxy, your web traffic will be send through a secure channel (SSH tunnel) towards the OCI instance and the OCI instance will appear as your browsers client IP for remote sites you visit.

An SSH server in combination with a locally running SOCKS proxy server allows you to browse the internet more securely from for example public Wifi hotspots by routing your internet traffic through a secure channel via a remote server. If you combine this with DNS over HTTPS, which is currently at least available in Firefox and Chrome, it will be more difficult for other parties to analyse your traffic. Also it allows you to access resources from a server outside of a company network which can have benefits for example if you want to check how a company hosted service looks to a customer from the outside. Having a server in a different country as a proxy can also have benefits if certain services are only available from a certain country (a similar benefit as using a VPN or using Tor) or as a means to circumvent censorship.

Do check what is allowed in your company, by your ISP and is legal within your country before using such techniques though. I of course don't want you to do anything illegal and blame me for it ;)