Much to my surprise, starting from the last week Kubernetes became the part of my job description. It’s no longer something just interesting to try, I actually have to understand it now. And as you probably could tell from my older k8s post, I’m not quite there. The post sort of builds a logical example (containerized web server) but something just doesn’t click.
I was trying to understand what’s missing, and it seems like the problem is in the tooling. You see, there’re two and a half ways to run something in Kubernetes. One is through ad-hoc commands, like
kubectl run or
kubectl expose. They are simple, but they also skip few important concepts happening in the background, so the whole picture stays unclear. Continue reading “Dissecting Kubernetes example”
Imagine your distributed app has two kinds of services:
db. Both of them are replicated for higher availability, live on different hosts, go online and offline whenever they like. So, here’s a question: how do
Obvious solution would be to come up with some sort of reliable key-value storage, and whenever service comes online, it would register itself with the address in the store. But what happens when service goes offline? It probably could notify the store just before that, but c’mon, it’s internet: things can go offline without any warning. OK, then we could implement some sort of service health checks to ensure that they are still available… By the way, did you notice how quickly the simple idea of using external store for service discovery started to become a reasonably large infrastructure project?
Service discovery is something very hard to do. But we don’t have to – there’re tools for that, and Consul is one of them. Continue reading “Using Consul for Service Discovery”
How do you usually configure an app? Over the decades our industry came up with multiple approaches, like providing command line arguments, various config files, registry settings and environment variables. Even hardcoding certain options into the app itself also works sometimes. Whenever we need to reconfigure the app we’d just go to its host, change a setting or two, and the job is done.
And now imagine a challenge: you have a cluster of services that come and go, they have different versions and locations, and you need to reconfigure all of them. How would you do that?
Continue reading “Using Consul Key-Value Store for Service Configuration”
ZeroMQ is small, fast and very easy to use messaging library, which works equally well both within the same process and over the network. Despite being written in C++, it has bindings for most of the languages you can come up with. And it’s free. Hurrah!
Working with ZeroMQ resembles working with TCP/UDP sockets. In fact, ZeroMQ endpoints are called sockets. You create one, bind it or connect to certain address, and then magic begins… But let’s see some code first and dive into the details as we go. Continue reading “Inter-service messaging with ZeroMQ and Node.js”