Kubernetes

From David's Wiki
Revision as of 03:25, 19 September 2021 by David (talk | contribs) (→‎Resources)
\( \newcommand{\P}[]{\unicode{xB6}} \newcommand{\AA}[]{\unicode{x212B}} \newcommand{\empty}[]{\emptyset} \newcommand{\O}[]{\emptyset} \newcommand{\Alpha}[]{Α} \newcommand{\Beta}[]{Β} \newcommand{\Epsilon}[]{Ε} \newcommand{\Iota}[]{Ι} \newcommand{\Kappa}[]{Κ} \newcommand{\Rho}[]{Ρ} \newcommand{\Tau}[]{Τ} \newcommand{\Zeta}[]{Ζ} \newcommand{\Mu}[]{\unicode{x039C}} \newcommand{\Chi}[]{Χ} \newcommand{\Eta}[]{\unicode{x0397}} \newcommand{\Nu}[]{\unicode{x039D}} \newcommand{\Omicron}[]{\unicode{x039F}} \DeclareMathOperator{\sgn}{sgn} \def\oiint{\mathop{\vcenter{\mathchoice{\huge\unicode{x222F}\,}{\unicode{x222F}}{\unicode{x222F}}{\unicode{x222F}}}\,}\nolimits} \def\oiiint{\mathop{\vcenter{\mathchoice{\huge\unicode{x2230}\,}{\unicode{x2230}}{\unicode{x2230}}{\unicode{x2230}}}\,}\nolimits} \)

Kubernetes, also known as K8s, is a container orchestration service by Google.
It supposedly has a harder learning curve than docker-swarm but is heavily inspired by Google's internal borg system.

Getting Started

Background

Kubernetes runs applications across nodes which are physical or virtual machines.
Each node contains a kubelet process, a container runtime, and possibly one or more pods.
Pods contain resources needed to host your application including volumes and containers.
Typically you will want one container per pod since deployments scale by creating multiple pods.

Installation

For local development, you can install minikube.
Otherwise, install kubeadm.

kubeadm

kubeadm install

Install Commands
Control Plane Init
Add worker nodes
Notes

Pods per node

How to increase pods per node
By default, Kubernetes allows 110 pods per node.
You may increase this up to a limit of 255 with the default networking subnet.
For reference, GCP GKE uses 110 pods per node and AWS EKS uses 250 pods per node.

kubectl

In general you will want to create a .yaml manifest and use apply, create, or delete to manage your resources.

nodes

kubectl get nodes

pods

kubectl get pods
kubectl describe pods

# Access a port on a pod
kubectl port-forward <pod> <localport:podport>

deployment

kubectl get deployments
kubectl logs $POD_NAME
kubectl exec -it $POD_NAME -- bash

# For one-off deployments of an image.
kubectl create deployment <name> --image=<image> [--replicas=1]

proxy

kubectl proxy

service

Services handle routing to your pods.

kubectl get services

kubectl expose deployment/<name> --type=<type> --port <port>
kubectl describe services/<name>

run

https://gc-taylor.com/blog/2016/10/31/fire-up-an-interactive-bash-pod-within-a-kubernetes-cluster

# Throw up a ubuntu container
kubectl run my-shell --rm -i --tty --image ubuntu -- bash
kubectl run busybox-shell --rm -i --tty --image odise/busybox-curl -- sh

Services

Documentation

Services handle networking.
For self-hosted/bare metal deployments, there are two types of services.

  • ClusterIP - This creates an IP address on the internal cluster which nodes and pods on the cluster can access. (Default)
  • NodePort - This exposes the port on every node. It implicitly creates a ClusterIP and every node will route to that. This allows access from outside the cluster.
  • ExternalName - uses a CNAME record. Primarily for accessing other services from within the cluster.

On managed deployments (e.g. AWS EKS, GKE) you also have

  • LoadBalancer - fires up the provider's load balancer

By default, ClusterIP is provided by kube-proxy and performs round-robin load-balancing to pods.

Ingress

Ingress | Kubernetes
Ingress is equivalent to having a load-balancer / reverse-proxy pod with a NodePort service.

Installing an Ingress Controller

See ingress-nginx to deploy an ingress controller.

Autoscaling

Horizontal Autoscale Walkthrough
Horizontal Pod Autoscaler

You will need to install metrics-server.
For testing, you may need to allow insecure tls.

Accessing External Services

access mysql on localhost
To access services running outside of your kubernetes cluster, including services running directly on a node, you need to add an endpoint and a service.

Example

Devices

Generic devices

See https://gitlab.com/arm-research/smarter/smarter-device-manager
and https://github.com/kubernetes/kubernetes/issues/7890#issuecomment-766088805

Intel GPU

See https://github.com/intel/intel-device-plugins-for-kubernetes/tree/main/cmd/gpu_plugin

After adding the gpu plugin, add the following to your deployment.

apiVersion: apps/v1
kind: Deployment
spec:
  template:
    spec:
      containers:
          resources:
            limits:
              gpu.intel.com/i915: 1

Variants

minikube

minikube is a tool to quickly set up a local Kubernetes cluster on your PC.

kind

k3s

k3s is a lighter-weight Kubernetes by Rancher Labs.

Resources