If, at any point, you’re considering creating a containerized application, then Kubernetes is the platform that instantly comes to mind. As the world’s leading containerized application platform, this is one of the most comprehensive ecosystems that developers can turn to, with their full documentation, a litany of tools, and advanced monitoring tools putting them ahead of the rest.
One huge part of what makes Kubernetes so effective to use is that it has comprehensive health monitoring tools. Kubernetes health checks cover a range of different functions, with distinct probes testing systems through various methods. These probes have one sole purpose – to double-check if your application is running correctly and is ready to process traffic.
Although extremely useful, many new developers that are just getting started in the world of Kubernetes aren’t sure how health checks work. With this in mind, we’ve created this beginner’s guide, introducing you to what health checks are, how probes work, and the overall state of your system.
Let’s get right into it.
What Are Health Checks in Kubernetes?
Within Kubernetes, to ensure that a specific container within a pod is ready to process traffic and perform all of its intended functions, the platform provides what are known as health checks. These mechanisms, also generally known as probes, are performed by Kubelet, helping to determine if a pod or container needs to restart or whether it’s ready to receive traffic.
In general, there are two types of health checks that are performed:
- Liveness – The liveness function, as you may have assumed from the title of this health check, allows a developer to establish if an application is dead or alive. This probe will assess the condition of the platform, removing the pod and replacing it if it is dead. If the pod is recognized as alive, then it will be left without any edits or changes being made. This check ensures that no dead pods are still used within the process, ensuring that only alive pods receive requests from your service.
- Readiness – An application doesn’t necessarily run 24/7, especially within the common Kubernetes ecosystem that could have thousands of different aspects all on the go at the same time. If you power up your service, any of the containers that are involved in the process will be pinged and will then start to get ready. However, to ensure that traffic isn’t sent before the app has actually started, Kubernetes has a readiness probe. This mechanism double checks that an app is ready, sending feedback to the server and telling it to hold off from delivering any requests until the app is in a completely functional state.
From these two health check mechanisms, Kubernetes will be able to establish if your system is running correctly, helping you to ensure that your system is always running correctly and at 100% functionality.
Are all Health Check Probes the Same Within Kubernetes?
While liveness and readiness are the two main mechanisms that are tested, they are not actually tested in the same way every single time. Within these two mechanisms, you can use three different health check probes.
The three probe types that will actively test both liveness and readiness are:
- HTTP – Anything to do with HTTP will always be the first type of probe that you turn to, as it is most effective within the largest majority of situations. Kubernetes will ping a specific path, hoping to get a response between the 200-350 range. If the response falls in this range, then the app is marked as completely healthy, with any response outside this range being unhealthy.
- TCP – A TCP probe attempts to establish a connection to a specified port within the Kubernetes container. If the probe does indeed establish the intended connection, then it’s working correctly; on the other hand, if it cannot, then the container is marked as unhealthy.
- Command – Command is the simplest of the three types, with Kubernetes sending a line of command code within a container. If the command returns a ‘0’, then the container is running correctly and will be marked as a healthy container. If anything else is returned, or nothing at all is received back, then the container will be marked as unhealthy, allowing you to conduct further analysis.
These checks are vital to ensure that your system is running correctly, with Kubernetes’ in-system health checks being one of the easiest ways of establishing the efficiency of your system. When you perform more checks, you’re able to create a foolproof system that will have a much higher uptime.
Why are Probes Important Within Kubernetes Health Checks?
Kubernetes systems can grow to be massive ecosystems, spanning across many servers and totaling thousands of different apps, nodes, and pods in total. Part of running a containerized system is that you have a lot of different moving parts to manage at once. While you have the final product output as a measure of the holistic success of your system, that does little to tell you about smaller sections.
As independent parts work to create a holistic whole within Kubernetes, probes allow you to test the state of these segmented parts. By using probes, you can see which components have failed, which are overloaded, or which are still initializing and aren’t yet ready.
With this information, you’re able to see your system’s health on an individual level, promoting a much healthier system in the long run.
With a comprehensive monitoring system in place, it’s no surprise that Kubernetes is able to provide such an extensive level of assessment for apps within your ecosystem. Expanding across several test methods and available information, Kubernetes will use a variety of different probes to assess the stability and activity of your system.
Using these monitoring tools will allow you to take control of your system, finding errors and ensuring that you have a near-perfect internal system balance. By focusing on testing and monitoring, you’re able to improve your app’s uptime and create a better overall final product.
Follow Techdee for more!