Kubernetes Getting Started
The basic you need to know when starting with Kubernetes.
Kubernetes provides a form of orchestration for your containers.
Assumptions
A Knowloedge of containers.
Through The History
Kubernetes is a open source code, that was created in 2014 by Google, using Golang. Now it’s maintained by Cloud Native Computing Foundation.
There is a paper of Google from 2015, talking about Google using Borg and Kubernetes. https://research.google/pubs/pub43438/
Another name to Kubernetes is K8S
K ubernete s
Kubernetes Component Architecture
Interesting to Know
Kubernetes support more container runtimes than just Docker
Container Runtime Interface (CRI)
- CRI-O
- Docker
- containerd
- Podman
Kubernetes Objects
There are some Kubernetes objects that you can create via yaml on your cluster.
Namespaces
These objects are a virtual separation of the deployments, services, and another objects on your cluster.
Ingress
Exposes HTTP and HTTPS to services on cluster.
Service
Provides access to your cluster. It can be ClusterIP, NodePort and LoadBalancer.
Service registry are based on DNS, so it creates a DNS for each service running.
Pod
Retains one or more containers
Deployment
It controls how Kubernetes will create pods, in terms of versions, enabling rollout and rollback, scalling, etc.
StatefulSet
Manage pods like Deployment, but with state of volumes.
ReplicaSet
It keeps the desired pods running
HorizontalAutoScaler
It scales the pods based on CPU and memory
PersistentVolume
Volume that maps volume on pod externally
DaemonSet
It makes all nodes, or some of them, run a particular pod
Job
Some command line script or similar
CronJob
It creates Job and schedules it
Hands on
apiVersion: v1
kind: Service
metadata:
name: my-nginx-svc
labels:
app: nginx
spec:
type: NodePort
ports:
- port: 80
targetPort: 80
nodePort: 30000
selector:
app: nginx
---
apiVersion: apps/v1
kind: Deployment
metadata:
name: my-nginx
labels:
app: nginx
spec:
replicas: 3
selector:
matchLabels:
app: nginx
template:
metadata:
labels:
app: nginx
spec:
containers:
- name: nginx
image: nginxdemos/hello:latest
ports:
- containerPort: 80
kubectl is the command line tool that we use to send the commands
Get all namespaces
kubectl get namespace
And, an alias to namespace here on K8S is ns, so you achieve the same thing using this other command below
kubectl get ns
Getting HorizontalAutoScaler
kubectl get horizontalpodautoscaler
And again, there is an alias, it’s hpa
Get pods within the namespace
kubectl -n <namespace> get pod
Scaling deployment horizontally
kubectl -n <namespace> scale --replicas=<desired_pods> deployment <deployment_name>
Get services
kubectl -n <namespace> get service
The alias is svc
See the logs
kubectl -n <namespace> logs pods/<running_pod>
See the logs in real time (“continuous tail”)
kubectl -n <namespace> logs -f pods/<running_pod>
You can also see the log from all the pods, filtering by label, like this
kubectl -n <namespace> logs -l app=<my_app_label>
Enter running pod
kubectl -n <namespace> exec --stdin --tty <running_pod> -- /bin/bash
To exit the pod, just type
exit
Deleting things
You can delete the pod using
kubectl -n <namespace> delete pod <running_pod>
Or even delete a deployment, using
kubectl -n <namespace> delete deployment <some_deployment>
Cluster Monitoring with Istio and Kiali
Downloading istioctl
curl -L https://istio.io/downloadIstio | sh -
cd istio-1.13.0
export PATH=$PWD/bin:$PATH
Installing
istioctl install --set profile=demo -y
Istio uses Envoy as sidecars
Injecting Envoy sidecar
kubectl label namespace default istio-injection=enabled
Result