Kubernetes Cheat Sheet| Mirantis (2023)

FAQs

What is Kubernetes cheat sheet? ›

Kubernetes is an open-source platform used to automate deployment and to scale containers across clusters of hosts providing container-centric infrastructure. It is a container orchestrator. It can run a Linux container. Become a master of DevOps by taking up this online instructor-led DevOps Training in London!

To resolve it, double check the pod specification and ensure that the repository and image are specified correctly. If this still doesn't work, there may be a network issue preventing access to the container registry. Look in the describe pod text file to obtain the hostname of the Kubernetes node.

The most basic command for viewing Kubernetes objects via kubectl is get . If you run kubectl get <resource-name> you will get a listing of all resources in the current namespace. If you want to get a specific resource, you can use kubectl get <resource-name> <object-name> .

While Docker is a container runtime, Kubernetes is a platform for running and managing containers from many container runtimes. Kubernetes supports numerous container runtimes including Docker, containerd, CRI-O, and any implementation of the Kubernetes CRI (Container Runtime Interface).

Kubectl controls the Kubernetes Cluster. It is one of the key components of Kubernetes which runs on the workstation on any machine when the setup is done. It has the capability to manage the nodes in the cluster. Kubectl commands are used to interact and manage Kubernetes objects and the cluster.

The kubelet works in terms of a PodSpec. A PodSpec is a YAML or JSON object that describes a pod. The kubelet takes a set of PodSpecs that are provided through various mechanisms (primarily through the apiserver) and ensures that the containers described in those PodSpecs are running and healthy.

So what exactly does ImagePullBackOff mean? The status ImagePullBackOff means that a Pod couldn't start, because Kubernetes couldn't pull a container image. The 'BackOff' part means that Kubernetes will keep trying to pull the image, with an increasing delay ('back-off').

Check the syslog and other container logs to see if this was caused by any of the issues we mentioned as causes of CrashLoopBackoff (e.g., locked or missing files). If not, then the problem could be with one of the third-party services. To verify this, you'll need to use a debugging container.

Overview. By default, GKE allows up to 110 Pods per node on Standard clusters, however Standard clusters can be configured to allow up to 256 Pods per node. Autopilot clusters have a maximum of 32 Pods per node.

How many containers can you run in a pod? ›

Remember that every container in a pod runs on the same node, and you can't independently stop or restart containers; usual best practice is to run one container in a pod, with additional containers only for things like an Istio network-proxy sidecar.

The key thing about pods is that when a pod does contain multiple containers, all of them are always run on a single worker node—it never spans multiple worker nodes, as shown in figure 3.1.

Kubectl stands for “Kubernetes Command-line interface”. It is a command-line tool for the Kubernetes platform to perform API calls. Kubectl is the main interface that allows users to create (and manage) individual objects or groups of objects inside a Kubernetes cluster.

Docker is still as popular as any container runtime in enterprise IT right now, but not for much longer. Kubernetes' Docker deprecation announcement has put Docker on a defined path towards irrelevancy in the enterprise space. It's a big changing of the guard, but don't view this as the end of Docker as a whole.

When it comes to learning Docker or Kubernetes first and you ask yourself do I need to learn Docker before Kubernetes? The answer is that you should instead learn about containerization engines.

You can decide to use Kubernetes without Docker, or even Docker without Kubernetes for that matter (but we advise you to use it for different purposes than running containers). Still, even though Kubernetes is a rather extensive tool, you will have to find a good container runtime for it – one that has implemented CRI.

Checking the logs of a running pod

All that you need to do to do that is to run the following command: kubectl logs nginx-7d8b49557c-c2lx9.

What is helm in Kubernetes? ›

Helm is a package manager for Kubernetes that makes it easy to take applications and services that are either highly repeatable or used in multiple scenarios and deploy them to a typical K8s cluster.

Pods always run on Nodes. A Node is a worker machine in Kubernetes and may be a VM or a physical machine, depending on the cluster. Each Node runs Pods and is managed by the Master. On a Node you can have multiple pods.

👍 Efficient resource usage

This includes, for example, the master nodes — a Kubernetes cluster typically has 3 master nodes, and if you have only a single cluster, you need only 3 master nodes in total (compared to 30 master nodes if you have 10 Kubernetes clusters).

kubectl is the command-line interface (CLI) tool for working with a Kubernetes cluster. Kubelet is the technology that applies, creates, updates, and destroys containers on a Kubernetes node.

If kubectl get pods shows that your pod status is ImagePullBackOff or ErrImagePull, this means that the pod could not run because it could not pull the image.

During the deployment of an application to a Kubernetes cluster, you'll typically want one or more images to be pulled from a Docker registry. In the application's manifest file you specify the images to pull, the registry to pull them from, and the credentials to use when pulling the images.

If a Pod is scheduled to a node that then fails, the Pod is deleted; likewise, a Pod won't survive an eviction due to a lack of resources or Node maintenance. Kubernetes uses a higher-level abstraction, called a controller, that handles the work of managing the relatively disposable Pod instances.

You can see them by simply putting --previous flag along with your kubectl logs ... cmd.

A Kubernetes cluster consists of the control plane and the worker nodes. To shrink this footprint, some projects have tried to strip nonessential elements out of Kubernetes to create a slimmed-down version.

How many Kubernetes masters do I need? ›

However, in case of Kubernetes HA environment, these important components are replicated on multiple masters(usually three masters) and if any of the masters fail, the other masters keep the cluster up and running.

A vSphere Pod is a VM with a small footprint that runs one or more Linux containers. Each vSphere Pod is sized precisely for the workload that it accommodates and has explicit resource reservations for that workload. It allocates the exact amount of storage, memory, and CPU resources required for the workload to run.

A Pod is is the smallest deployable unit that can be deployed and managed by Kubernetes. In other words, if you need to run a single container in Kubernetes, then you need to create a Pod for that container. At the same time, a Pod can contain more than one container, if these containers are relatively tightly coupled.

Workloads use metadata resources, which are the objects used to configure the behavior of other resources within the cluster. Workloads will eventually run a container, but to run a container, you will need to run a Pod. It is possible to create a Pod as a standalone object.

As the official documentation puts it: “A pod (as in a pod of whales or pea pod) is a group of one or more containers, with shared storage/network resources, and a specification for how to run the containers.” So, in the simplest terms possible, a pod is the mechanism for how a container actually gets turned “on” in ...

Pods are simply the smallest unit of execution in Kubernetes, consisting of one or more containers, each with one or more application and its binaries. Nodes are the physical servers or VMs that comprise a Kubernetes Cluster.

A Pod can communicate with another Pod by directly addressing its IP address, but the recommended way is to use Services. A Service is a set of Pods, which can be reached by a single, fixed DNS name or IP address. In reality, most applications on Kubernetes use Services as a way to communicate with each other.

Worker nodes are generally more powerful than master nodes because they have to run hundreds of clusters on them. However, master nodes hold more significance because they manage the distribution of workload and the state of the cluster.

Kubectl get pods

This command lists pods on the Kubernetes cluster. This command works for all types of Kubernetes resources: pods, services, deployments, cronjobs, events, ingresses, etc. We can also add parameters: --all-namespaces : List all resources of all namespaces.

To find the cluster IP address of a Kubernetes pod, use the kubectl get pod command on your local machine, with the option -o wide . This option will list more information, including the node the pod resides on, and the pod's cluster IP. The IP column will contain the internal cluster IP address for each pod.

How do I get container logs in Kubernetes? ›

You can see the logs of a particular container by running the command kubectl logs <container name> . Here's an example for Nginx logs generated in a container. If you want to access logs of a crashed instance, you can use –previous . This method works for clusters with a small number of containers and instances.

The name Kubernetes originates from Greek, meaning helmsman or pilot. K8s as an abbreviation results from counting the eight letters between the "K" and the "s". Google open-sourced the Kubernetes project in 2014.

It's true that most conventional PaaS platforms have disappeared. Yet if you look at Kubernetes, the massively popular open-source orchestrator, PaaS is alive and well. In many ways, Kubernetes is basically just PaaS by another name (and with less vendor lock-in).

A pod is the smallest execution unit in Kubernetes. A pod encapsulates one or more applications. Pods are ephemeral by nature, if a pod (or the node it executes on) fails, Kubernetes can automatically create a new replica of that pod to continue operations.

For example, Kubernetes may run 10 containers with a memory request value of 1 GB on a node with 10 GB memory. However, if these containers have a memory limit of 1.5 GB, some of the pods may use more than the minimum memory, and then the node will run out of memory and need to kill some of the pods.

One CPU, in Kubernetes, is equivalent to: 1 AWS vCPU. 1 GCP Core. 1 Azure vCore. 1 Hyperthread on a bare-metal Intel processor with Hyperthreading.

Kubernetes uses memory requests to determine on which node to schedule the pod. For example, on a node with 8 GB free RAM, Kubernetes will schedule 10 pods with 800 MB for memory requests, five pods with 1600 MB for requests, or one pod with 8 GB for request, etc.

Kubernetes is a portable, extensible, open source platform for managing containerized workloads and services, that facilitates both declarative configuration and automation. It has a large, rapidly growing ecosystem. Kubernetes services, support, and tools are widely available.

With that out of the way, Kubernetes is an open source container orchestration system that is portable, extensible, and not only allows you to deploy those containers to a scalable cluster, but it can be used (with the addition of other tools) to completely automate the orchestration of your containerized applications.

There are four types of Kubernetes services — ClusterIP , NodePort , LoadBalancer and ExternalName .

How easy is Kubernetes? ›

Kubernetes is the standard in container orchestration and deployment management. Kubernetes can be difficult to learn for someone only familiar with traditional hosting and development environments.

The primary options you can choose instead of Kubernetes are: Container as a Service (CaaS)—services like AWS Fargate and Azure Container Instances, which allow you to manage containers at scale without the complex orchestration capabilities provided by Kubernetes.

Among the reasons why Kubernetes has been so widely adopted are flexibility and lack of fragmentation. Kubernetes may not be perfect, but there's no denying that a lot of people love it. Indeed, Kubernetes provides orchestration for more than three-quarters of containerized applications today.

Kubernetes (also known as k8s or “kube”) is an open source container orchestration platform that automates many of the manual processes involved in deploying, managing, and scaling containerized applications.

The Kubernetes server runs locally within your Docker instance, is not configurable, and is a single-node cluster. It runs within a Docker container on your local system, and is only for local testing.

Remember that every container in a pod runs on the same node, and you can't independently stop or restart containers; usual best practice is to run one container in a pod, with additional containers only for things like an Istio network-proxy sidecar.

Pods are simply the smallest unit of execution in Kubernetes, consisting of one or more containers, each with one or more application and its binaries. Nodes are the physical servers or VMs that comprise a Kubernetes Cluster.

The Kubernetes Platform contains control over the resources related to Storage and Compute. These resources are regarded as Objects, and it contains 8 Key objects.

Kubernetes objects are entities that are used to represent the state of the cluster. An object is a “record of intent” – once created, the cluster does its best to ensure it exists as defined. This is known as the cluster's “desired state.”