Kubernetes: Difference between revisions

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==Getting Started==

===Background===

Kubernetes runs applications across nodes which are physical or virtual machines.

Kubernetes runs applications across '''nodes''' which are (physical or virtual) Linux machines.

Each node contains a kubelet process, a container runtime (typically containerd), and any running pods.

Pods contain resources needed to host your application including volumes and containers.

'''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.

Typically you will want one container per pod since deployments scale by creating multiple pods.

A '''deployment''' is a rule which spawns and manages pods.

A '''service''' is a networking rule which allows connecting to pods.

In addition to standard Kubernetes objects, '''operators''' watch for and allow you to instantiate custom resources (CR).

==Kubeadm Administration==

Notes on administering kubernetes clusters.

Kuberenetes has many parts and administration is very tedious which is why K3S exists. I'd recommend against using kubeadm for a homelab.

===Installation===

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</syntaxhighlight>

}}

===Certificates===

[https://kubernetes.io/docs/tasks/administer-cluster/kubeadm/kubeadm-certs/ Certificate Management with kubeadm]

Kubernetes requires several TLS certificates which are automatically generated by Kubeadm.

These expire in one year but are automatically renewed whenever you upgrade your cluster with <code>kubeadm upgrade apply</code>

To renew the certificates manually, run <code>kubeadm certs renew all</code> and restart your control plane services.

Note that if you lets the certificates expire, you will need to setup kubectl again.

Issues connecting with etcd

I ran into this when trying to kubeadm upgrade

;context deadline exceeded remote error: tls: bad certificate

Kubeadm stores etcd certificates in <code>/etc/kubernetes/pki/etcd/</code>.

Follow this to generate new certificates: https://github.com/etcd-io/etcd/issues/9785#issuecomment-432438748

You will need to create a temporary files for ca-config.json and server.json to generate new keys.

Make sure in the server.json to set the key algo to "rsa" and size to 2048. In the same file, set your CN to 127.0.0.1 and the hosts to [127.0.0.1, your local IP].

;cannot validate certificate for 127.0.0.1 because it doesn't contain any IP SANs

This means your hosts in server.json is not correct when you generated the new keys.

===Pods per node===

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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.

===Changing Master Address===

See https://ystatit.medium.com/how-to-change-kubernetes-kube-apiserver-ip-address-402d6ddb8aa2

==kubectl==

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kubectl run busybox-shell --rm -i --tty --image odise/busybox-curl -- sh

</syntaxhighlight>

==Deployments==

In most cases, you will use deployments to provision pods.

Deployments internally use replicasets to create multiple identical pods.

This is great for things such as webservers or standalone services which are not stateful.

In most cases, you can stick a service in front which will round-robin requests to different pods in your deployment.

{{hidden | Example Deployment |

apiVersion: apps/v1

kind: Deployment

metadata:

labels:

app: nextcloud

spec:

replicas: 1

selector:

matchLabels:

pod-label: nextcloud-app-pod

template:

metadata:

labels:

pod-label: nextcloud-app-pod

spec:

containers:

- name: nextcloud

image: public.ecr.aws/docker/library/nextcloud:stable

ports:

- containerPort: 80

env:

- name: MYSQL_HOST

value: nextcloud-db-service

- name: MYSQL_DATABASE

value: nextcloud

- name: MYSQL_USER

valueFrom:

secretKeyRef:

key: username

- name: MYSQL_PASSWORD

valueFrom:

secretKeyRef:

key: password

volumeMounts:

- name: nextcloud-app-storage

mountPath: /var/www/html

volumes:

- name: nextcloud-app-storage

persistentVolumeClaim:

claimName: nextcloud-app-pvc

</syntaxhighlight>

}}

==StatefulSets==

[https://kubernetes.io/docs/tutorials/stateful-application/basic-stateful-set/ StatefulSets basics]

Stateful sets are useful when you need a fixed number of pods with stable identities such as databases.

Pods created by stateful sets have a unique number suffix which allows you to query a specific pod.

Typically, you will want to use a headless service (i.e. without ClusterIP) to give local dns records to each service.

In most cases, you will want to look for a helm chart instead of creating your own stateful sets.

==Services==

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Services handle networking.

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

For self-hosted/bare metal clusters, 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.

* LoadBalancer - Creates a clusterip+nodeport and tells the loadbalancer to create an IP and route it to the nodeport.

** On bare-metal ~~deployments~~ you will need to install a loadbalancer such as metallb.

** On bare-metal clusters you will need to install a loadbalancer such as metallb.

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

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==Ingress==

[https://kubernetes.io/docs/concepts/services-networking/ingress/ Ingress | Kubernetes]

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

An ingress is an http endpoint. This configures an ingress controller which is a load-balancer or reverse-proxy pod that integrates with Kubernetes.

A common ingress controller is [https://github.com/kubernetes/ingress-nginx ingress-nginx] which is maintained by the Kubernetes team. Alternatives include [https://docs.nginx.com/nginx-ingress-controller/installation/installing-nic/installation-with-helm/ nginx-ingress] [https://doc.traefik.io/traefik/providers/kubernetes-ingress/ traefik], [https://haproxy-ingress.github.io/ haproxy-ingress], and [https://kubernetes.io/docs/concepts/services-networking/ingress-controllers/ others].

===Installing ingress-nginx===

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type: LoadBalancer

loadBalancerIP: 192.168.1.3

externalTrafficPolicy: Local

config:

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# Then you can simply add the following annotations to your ingresses to protect them:

#:<syntaxhighlight lang="yaml">

nginx.ingress.kubernetes.io/auth-url: "~~https~~://oauth2proxy.~~davidl~~.me/oauth2/[email protected]"

nginx.ingress.kubernetes.io/auth-url: "http://oauth2proxy.default.svc.cluster.local/oauth2/[email protected]"

nginx.ingress.kubernetes.io/auth-signin: "https://oauth2proxy.davidl.me/oauth2/start?rd=$scheme://$host$request_uri"

</syntaxhighlight>

;Additional things to look into

* Pomerium

* Keycloak

** https://www.talkingquickly.co.uk/webapp-authentication-keycloak-OAuth2-proxy-nginx-ingress-kubernetes

* Authelia - only supports username/password as the first factor

* Authentik - tried this but had too complicated and buggy for me.

If you use Cloudflare, you can also use Cloudflare access, though make sure you prevent other sources from accessing the service directly.

==Autoscaling==

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===Scale to 0===

[https://stackoverflow.com/questions/64133011/scale-down-kubernetes-deployments-to-0-and-scale-back-to-original-number-of-repl reference]

If you wish to restart your cluster, you can scale your deployments and stateful sets down to 0 and then scale them back up after.

If you wish to restart all nodes of your cluster, you can scale your deployments and stateful sets down to 0 and then scale them back up after.

# Annotate existing deployments and statefulsets with replica count.

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==Helm==

Helm is a method for deploying ~~application~~ using premade kubernetes manifest templates known as helm charts.

Helm is a method for deploying applications using premade kubernetes manifest templates known as helm charts.

~~Rather than writing your own manifest or copying a manifest from elsewhere~~, you ~~can use helm charts which create and install kubernetes manifests~~.

Helm charts abstract away manifests, allowing you to focus on only the important configuration values.

Manifests can also be composed into other manifests for applications which require multiple microservices.

[https://artifacthub.io/ https://artifacthub.io/] allows you to search for helm charts others have made.

[https://github.com/bitnami/charts bitnami/charts] contains helm charts for many popular applications.

===Usage===

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# Install the application using helm.

#:<pre>helm upgrade --install $NAME $CHARTNAME -f values.yaml [--version $VERSION]</pre>

===Troubleshooting===

Sometimes, Kubernetes will deprecate APIs, preventing it from managing existing helm releases.

The [https://github.com/helm/helm-mapkubeapis mapkubeapis] helm plugin can help resolve some of these issues.

==Variants==

===minikube===

[https://minikube.sigs.k8s.io/docs/ minikube] is a tool to quickly set up a local Kubernetes ~~cluster~~ on your PC.

[https://minikube.sigs.k8s.io/docs/ minikube] is a tool to quickly set up a local Kubernetes dev environment on your PC.

===kind===

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===k3s===

[https://k3s.io/ k3s] is a lighter-weight Kubernetes by Rancher Labs.

It includes Flannel CNI and Traefik Ingress Controller.

==KubeVirt==

KubeVirt allows you to run virtual machines ~~with vGPU support~~ on your Kubernetes cluster.

KubeVirt allows you to run virtual machines on your Kubernetes cluster.

==Resources==

* [https://kubernetes.io/docs/tutorials/kubernetes-basics/ Kubernetes Basics]

* [https://www.udemy.com/course/certified-kubernetes-administrator-with-practice-tests/ Certified Kubernetes Administrator (CKA) with Practice Tests (~$15)]

* [https://yolops.net/k8s-dualstack-cilium.html https://yolops.net/k8s-dualstack-cilium.html]

@@ Line 5: / Line 5: @@
 ==Getting Started==
 ===Background===
-Kubernetes runs applications across nodes which are physical or virtual machines.<br>
+Kubernetes runs applications across '''nodes''' which are (physical or virtual) Linux machines.<br>
 Each node contains a kubelet process, a container runtime (typically containerd), and any running pods.<br>
-Pods contain resources needed to host your application including volumes and containers.<br>
+'''Pods''' contain resources needed to host your application including volumes and containers.<br>
-Typically you will want one container per pod since deployments scale by creating multiple pods.
+Typically you will want one container per pod since deployments scale by creating multiple pods.<br>
+A '''deployment''' is a rule which spawns and manages pods.<br>
+A '''service''' is a networking rule which allows connecting to pods.
+In addition to standard Kubernetes objects, '''operators''' watch for and allow you to instantiate custom resources (CR).
+==Kubeadm Administration==
+Notes on administering kubernetes clusters.
+Kuberenetes has many parts and administration is very tedious which is why K3S exists. I'd recommend against using kubeadm for a homelab.
 ===Installation===
@@ Line 190: / Line 199: @@
 </syntaxhighlight>
 }}
+===Certificates===
+[https://kubernetes.io/docs/tasks/administer-cluster/kubeadm/kubeadm-certs/ Certificate Management with kubeadm]
+Kubernetes requires several TLS certificates which are automatically generated by Kubeadm.
+These expire in one year but are automatically renewed whenever you upgrade your cluster with <code>kubeadm upgrade apply</code>
+To renew the certificates manually, run <code>kubeadm certs renew all</code> and restart your control plane services.
+Note that if you lets the certificates expire, you will need to setup kubectl again.
+Issues connecting with etcd
+I ran into this when trying to kubeadm upgrade
+;context deadline exceeded remote error: tls: bad certificate
+Kubeadm stores etcd certificates in <code>/etc/kubernetes/pki/etcd/</code>.
+Follow this to generate new certificates: https://github.com/etcd-io/etcd/issues/9785#issuecomment-432438748
+You will need to create a temporary files for ca-config.json and server.json to generate new keys.
+Make sure in the server.json to set the key algo to "rsa" and size to 2048. In the same file, set your CN to 127.0.0.1 and the hosts to [127.0.0.1, your local IP].
+;cannot validate certificate for 127.0.0.1 because it doesn't contain any IP SANs
+This means your hosts in server.json is not correct when you generated the new keys.
 ===Pods per node===
@@ Line 196: / Line 226: @@
 You may increase this up to a limit of 255 with the default networking subnet.<br>
 For reference, GCP GKE uses 110 pods per node and AWS EKS uses 250 pods per node.
+===Changing Master Address===
+See https://ystatit.medium.com/how-to-change-kubernetes-kube-apiserver-ip-address-402d6ddb8aa2
 ==kubectl==
@@ Line 254: / Line 287: @@
 kubectl run busybox-shell --rm -i --tty --image odise/busybox-curl -- sh
 </syntaxhighlight>
+==Deployments==
+In most cases, you will use deployments to provision pods.<br>
+Deployments internally use replicasets to create multiple identical pods.<br>
+This is great for things such as webservers or standalone services which are not stateful.
+In most cases, you can stick a service in front which will round-robin requests to different pods in your deployment.
+{{hidden | Example Deployment |
+<syntaxhighlight lang="yaml">
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: nextcloud-app
+  labels:
+    app: nextcloud
+spec:
+  replicas: 1
+  selector:
+    matchLabels:
+      pod-label: nextcloud-app-pod
+  template:
+    metadata:
+      labels:
+        pod-label: nextcloud-app-pod
+    spec:
+      containers:
+        - name: nextcloud
+          image: public.ecr.aws/docker/library/nextcloud:stable
+          ports:
+            - containerPort: 80
+          env:
+            - name: MYSQL_HOST
+              value: nextcloud-db-service
+            - name: MYSQL_DATABASE
+              value: nextcloud
+            - name: MYSQL_USER
+              valueFrom:
+                secretKeyRef:
+                  name: nextcloud-db-credentials
+                  key: username
+            - name: MYSQL_PASSWORD
+              valueFrom:
+                secretKeyRef:
+                  name: nextcloud-db-credentials
+                  key: password
+          volumeMounts:
+            - name: nextcloud-app-storage
+              mountPath: /var/www/html
+      volumes:
+        - name: nextcloud-app-storage
+          persistentVolumeClaim:
+            claimName: nextcloud-app-pvc
+</syntaxhighlight>
+}}
+==StatefulSets==
+[https://kubernetes.io/docs/tutorials/stateful-application/basic-stateful-set/ StatefulSets basics]<br>
+Stateful sets are useful when you need a fixed number of pods with stable identities such as databases.<br>
+Pods created by stateful sets have a unique number suffix which allows you to query a specific pod.<br>
+Typically, you will want to use a headless service (i.e. without ClusterIP) to give local dns records to each service.
+In most cases, you will want to look for a helm chart instead of creating your own stateful sets.
 ==Services==
@@ Line 259: / Line 354: @@
 Services handle networking.
-For self-hosted/bare metal deployments, there are two types of services.
+For self-hosted/bare metal clusters, 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.
 * LoadBalancer - Creates a clusterip+nodeport and tells the loadbalancer to create an IP and route it to the nodeport.
-** On bare-metal deployments you will need to install a loadbalancer such as metallb.
+** On bare-metal clusters you will need to install a loadbalancer such as metallb.
 By default, ClusterIP is provided by <code>kube-proxy</code> and performs round-robin load-balancing to pods.<br>
@@ Line 289: / Line 384: @@
 ==Ingress==
 [https://kubernetes.io/docs/concepts/services-networking/ingress/ Ingress | Kubernetes]<br>
-Ingress is equivalent to having a load-balancer / reverse-proxy pod with a NodePort service.
+An ingress is an http endpoint. This configures an ingress controller which is a load-balancer or reverse-proxy pod that integrates with Kubernetes.
+A common ingress controller is [https://github.com/kubernetes/ingress-nginx ingress-nginx] which is maintained by the Kubernetes team. Alternatives include [https://docs.nginx.com/nginx-ingress-controller/installation/installing-nic/installation-with-helm/ nginx-ingress] [https://doc.traefik.io/traefik/providers/kubernetes-ingress/ traefik], [https://haproxy-ingress.github.io/ haproxy-ingress], and [https://kubernetes.io/docs/concepts/services-networking/ingress-controllers/ others].
 ===Installing ingress-nginx===
@@ Line 329: / Line 426: @@
      type: LoadBalancer
      loadBalancerIP: 192.168.1.3
+    externalTrafficPolicy: Local
    config:
@@ Line 389: / Line 487: @@
 # Then you can simply add the following annotations to your ingresses to protect them:
 #:<syntaxhighlight lang="yaml">
-nginx.ingress.kubernetes.io/auth-url: "https://oauth2proxy.davidl.me/oauth2/[email protected]"
+nginx.ingress.kubernetes.io/auth-url: "http://oauth2proxy.default.svc.cluster.local/oauth2/[email protected]"
 nginx.ingress.kubernetes.io/auth-signin: "https://oauth2proxy.davidl.me/oauth2/start?rd=$scheme://$host$request_uri"
 </syntaxhighlight>
+;Additional things to look into
+* Pomerium
+* Keycloak
+** https://www.talkingquickly.co.uk/webapp-authentication-keycloak-OAuth2-proxy-nginx-ingress-kubernetes
+* Authelia - only supports username/password as the first factor
+* Authentik - tried this but had too complicated and buggy for me.
+If you use Cloudflare, you can also use Cloudflare access, though make sure you prevent other sources from accessing the service directly.
 ==Autoscaling==
@@ Line 486: / Line 593: @@
 ===Scale to 0===
 [https://stackoverflow.com/questions/64133011/scale-down-kubernetes-deployments-to-0-and-scale-back-to-original-number-of-repl reference]<br>
-If you wish to restart your cluster, you can scale your deployments and stateful sets down to 0 and then scale them back up after.
+If you wish to restart all nodes of your cluster, you can scale your deployments and stateful sets down to 0 and then scale them back up after.
 <syntaxhighlight lang="bash">
 # Annotate existing deployments and statefulsets with replica count.
@@ Line 504: / Line 611: @@
 ==Helm==
-Helm is a method for deploying application using premade kubernetes manifest templates known as helm charts.<br>
+Helm is a method for deploying applications using premade kubernetes manifest templates known as helm charts.<br>
-Rather than writing your own manifest or copying a manifest from elsewhere, you can use helm charts which create and install kubernetes manifests.<br>
+Helm charts abstract away manifests, allowing you to focus on only the important configuration values.<br>
 Manifests can also be composed into other manifests for applications which require multiple microservices.
+[https://artifacthub.io/ https://artifacthub.io/] allows you to search for helm charts others have made.<br>
+[https://github.com/bitnami/charts bitnami/charts] contains helm charts for many popular applications.
 ===Usage===
@@ Line 514: / Line 624: @@
 # Install the application using helm.
 #:<pre>helm upgrade --install $NAME $CHARTNAME -f values.yaml [--version $VERSION]</pre>
+===Troubleshooting===
+Sometimes, Kubernetes will deprecate APIs, preventing it from managing existing helm releases.<br>
+The [https://github.com/helm/helm-mapkubeapis mapkubeapis] helm plugin can help resolve some of these issues.
 ==Variants==
 ===minikube===
-[https://minikube.sigs.k8s.io/docs/ minikube] is a tool to quickly set up a local Kubernetes cluster on your PC.
+[https://minikube.sigs.k8s.io/docs/ minikube] is a tool to quickly set up a local Kubernetes dev environment on your PC.
 ===kind===
@@ Line 523: / Line 637: @@
 ===k3s===
 [https://k3s.io/ k3s] is a lighter-weight Kubernetes by Rancher Labs.
+It includes Flannel CNI and Traefik Ingress Controller.
 ==KubeVirt==
 {{main | KubeVirt}}
-KubeVirt allows you to run virtual machines with vGPU support on your Kubernetes cluster.
+KubeVirt allows you to run virtual machines on your Kubernetes cluster.
 ==Resources==
 * [https://kubernetes.io/docs/tutorials/kubernetes-basics/ Kubernetes Basics]
 * [https://www.udemy.com/course/certified-kubernetes-administrator-with-practice-tests/ Certified Kubernetes Administrator (CKA) with Practice Tests (~$15)]
+* [https://yolops.net/k8s-dualstack-cilium.html https://yolops.net/k8s-dualstack-cilium.html]