Kubernetes

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Useful

alias: 

alias k="kubectl"
alias ks="kubectl --namespace kube-system"                                          # Kubernetes Events
alias ke="kubectl get events --sort-by='{.lastTimestamp}'"                          # Kubernetes System stuff
alias kse="kubectl --namespace kube-system get events --sort-by='{.lastTimestamp}'" # Kubernetes Systems Events

dump all : 

kubectl get all --export=true -o yaml

( namespace kube-system not dumped )

list form: 

k get pods
k get rs # replica set
k get rc # replication controller

what are all the things ? 

kubectl api-resources

event sorted by time 

kubectl get events --sort-by=.metadata.creationTimestamp

what storage classes does my cluster support? 

k get storageclass

how are pod spread out over nodes: 

k describe node | grep -E '(^Non-t|m |^Name)' | more

( doesn't scale well, no indication of )

what deployments should be on what instance groups: 

kubectl get deploy --all-namespaces -o=jsonpath='{range .items[*]}{.metadata.name}{"\t"}{..nodeSelector}{"\n"}{end}' |sort

or the other way round ( ig first ) 

kubectl get deploy --all-namespaces -o=jsonpath='{range .items[*]}{..nodeSelector}{"\t"}{.metadata.name}{"\n"}{end}' |sort

if you used kops to deploy the cluster then nodes are labes with their instance groups, you can be more specific like this: 

k describe node -l kops.k8s.io/instancegroup=<instance group name> | grep -E '(^Non-t|m |^Name)' | more

how many nods in each instance group? ( tested under kops ) 

for i in `kops get ig 2>/dev/null| grep -v NAME | awk '{print $1}'`
do
echo $i
kubectl get nodes -l kops.k8s.io/instancegroup=$i
done

how many pods per node: 

k get pod -o wide | grep -v NAME | awk '{print $8}' | sort | uniq -c | sort -rn

k get pod --all-namespaces -o wide | grep -v NAME | awk '{print $8}' | sort | uniq -c | sort -rn

audit: who tried to do what? 

ks get pod | grep kube-apiserver-ip

ks logs $podname

who tried to scale unsuccessfully? 

ks logs $podname | grep scale | grep cloud | awk '$8!=200{print $0}'

Where is the service account token that I gave this pod?

It's in here: /var/run/secrets/kubernetes.io/serviceaccount/token

Scripting Scaling

Manually edit the replicas of a deployment from within the same namespace, but in a different pod:

  1. give the actor pod a service account ( possibly via it's deployment ).
  2. create a Role as below.
  3. create the RoleBinding to connect the ServiceAccount to the Role.

Now you have: Pod -> Deployment -> ServiceAccount -> RoleBinding -> Role

Now the Pod has permission to do what it needs. Very similar to AWS's "IAM Role" where you give an instance a role that has the permissions that it needs to operate.

Note that in this case "ClusterRole" and ClusterRoleBinding are not required. It's all namespaced to the namespace that your deployment is in. In this case: "default". 

export API_URL="https://${KUBERNETES_SERVICE_HOST}:${KUBERNETES_SERVICE_PORT}/${KUBE_ENDPOINT}"
export TOKEN=`cat /var/run/secrets/kubernetes.io/serviceaccount/token`
export CURL_CA_BUNDLE=/var/run/secrets/kubernetes.io/serviceaccount/ca.crt

curl \
 -H 'Accept: application/json' \
 -H "Authorization: Bearer $TOKEN" \
 $API_URL \
 > scale.json
# edit scale.json, set replicas to 4
curl -X PUT \
 -d@scale.json \
 -H 'Content-Type: application/json' \
 -H "Authorization: Bearer $TOKEN" \
 $API_URL

CURL_CA_BUNDLE - kubenerets is it's own CA, and presennts to each pod a ca bundle that makes ssl "in" the cluster valid.

This was the role that did it. FIXME: pare it down 

apiVersion: rbac.authorization.k8s.io/v1
kind: Role
metadata:
  name: kube-cloudwatch-autoscaler
  labels:
    app: kube-cloudwatch-autoscaler
rules:
- apiGroups:
  - ""
  resources:
  - nodes
  verbs:
  - list
- apiGroups:
  - apps
  resources:
  - deployments
  - deployments.apps
  - deployments.apps/scale
  - "*/scale"
  verbs:
  - get
  - update
  - patch
  - put
- apiGroups:
  - ""
  resources:
  - configmaps
  verbs:
  - get
  - create

On patching

There are a couple of way to change an object. 

export TOKEN=`cat /var/run/secrets/kubernetes.io/serviceaccount/token`
export CURL_CA_BUNDLE=/var/run/secrets/kubernetes.io/serviceaccount/ca.crt

1. dump whole "thing" , make change post object back ( as above ) GET -> PUT 

curl \
 -v \
 -H 'Accept: application/json' \
 -H "Authorization: Bearer $TOKEN" \
 $API_URL \
 > scale.json
# edit scale.json, set replicas to 4
curl -X PUT \
 -d@scale.json \
 -H 'Content-Type: application/json' \
 -H "Authorization: Bearer $TOKEN" \
 $API_URL

2. terse PATCH 

curl -sS \
 -X 'PATCH' \
 -H "Authorization: Bearer ${TOKEN}" \
 -H 'Content-Type: application/merge-patch+json' \
 $API_URL \
 -d '{"spec": {"replicas":  1}}'

3. old / full PATCH ?

reference: https://stackoverflow.com/questions/41792851/manage-replicas-count-for-deployment-using-kubernetes-api ( 1 year 8 months old at tie of _this_ writing )

Careful, compare:

BORKEN! 

PAYLOAD='[{"op":"replace","path":"/spec/replicas","value":"3"}]'
curl \
 -X PATCH \
 -d ${PAYLOAD} \
 -H 'Content-Type: application/json-patch+json' \
 -H "Authorization: Bearer ${TOKEN}" \
 $API_URL

WERKS! 

curl \
 -X PATCH \
 -d '[{"op":"replace","path":"/spec/replicas","value":3}]' \
 -H 'Content-Type: application/json-patch+json' \
 -H "Authorization: Bearer ${TOKEN}" \
 $API_URL

Closely: 

-d '[{"op":"replace","path":"/spec/replicas","value":"3"}]'  <- broken
-d '[{"op":"replace","path":"/spec/replicas","value":3}]' <- works

Template Examples

list images by pod: 

kubectl get pods --all-namespaces -o=jsonpath='{range .items[*]}{"\n"}{.metadata.name}{":\t"}{range .spec.containers[*]}{.image}{", "}{end}{end}{"\n"}'

list images by deploy 

kubectl get deploy -o=jsonpath='{range .items[*]}{"\n"}{.metadata.name}{":\t"}{range .spec.template.spec.containers[*]}{.image}{", "}{end}{end}{"\n"}'

list all deploy cpu nd mem requet: 

kubectl get deploy -o=jsonpath='{range .items[*]}{"\n"}{.metadata.name}{":\t"}{range .spec.template.spec.containers[*]}{.resources.requests.cpu}{", "}{.resources.requests.memory}{end}{end}{"\n"}'

list nodeslectors for all deploys: 

kubectl get deploy -o=jsonpath='{range .items[*]}{"\n"}{.metadata.name}{":\t"}{.spec.template.spec.nodeSelector}{end}{"\n"}'

all nodes by their condition statuses: 

kubectl get nodes -o=jsonpath='{range .items[*]}{@.metadata.name}:{"\n"}{range @.status.conditions[*]}{"\t"}{@.type}={@.status};{"\n"}{end}{end}{"\n"}'

Note the double loop.

examine the resource requesnt and limit for all deploys: 

kubectl get deploy -o=jsonpath='{range .items[*]}{@.metadata.name}{range @.spec.template.spec.containers[*]}{@.resources.request.cpu}{@.resources.request.memory}{@.resources.limits.cpu}{@.resources.limits.memory}{"\n"}{end}{end}{"\n"}'


WIP

metrics

wget "$(kubectl config view -o jsonpath='{range .clusters[*]}{@.cluster.server}{"\n"}{end}')"

Troubleshooting

look at logs:

put this in a deployment so that you can exec into a failing pod and see what it's upto: 

       command: ["/bin/sh"]
       args: ["-c", "while true; do date; sleep 10;done"]

Practices and Guidlines

  • Do not use replication controllers, instead use replica sets
  • when changing the shape of the cluster , number and type of instance groups , you will use kops edit ig <ig name> , but don't for get to update the cluster-autoscaler config ( ks edit deploy cluster-autoscaler )

Cgroup / slice errors

https://github.com/kubernetes/kubernetes/issues/56850

log message: 

Sep 18 21:32:37 ip-10-10-37-50 kubelet[1681]: E0918 21:32:37.901058    1681 summary.go:92] Failed to get system container stats for "/system.slice/docker.service": failed to get cgroup stats for "/system.slice/docker.service": failed to get container info for "/system.slice/docker.service": unknown container "/system.slice/docker.service"

MAAS ubuntu

https://stripe.com/blog/operating-kubernetes

https://cloudplatform.googleblog.com/2018/05/Kubernetes-best-practices-Setting-up-health-checks-with-readiness-and-liveness-probes.html

https://medium.com/@adriaandejonge/moving-from-docker-to-rkt-310dc9aec938

https://coreos.com/rkt/docs/latest/rkt-vs-other-projects.html#rkt-vs-docker

https://hackernoon.com/docker-containerd-standalone-runtimes-heres-what-you-should-know-b834ef155426?gi=3c7edac0b22d


Security

Todo / read:

References and Reading

Replica set versus Replication controller
https://www.mirantis.com/blog/kubernetes-replication-controller-replica-set-and-deployments-understanding-replication-options/
Publishing services - service types
https://kubernetes.io/docs/concepts/services-networking/service/#publishing-services-service-types
Kuberenetes the hard way
https://github.com/kelseyhightower/kubernetes-the-hard-way

HPA broken

Blue is test

Blue env: 

Client Version: v1.12.2
Server Version: v1.10.6

Prod env: 

Client Version: v1.12.2
Server Version: v1.9.8

In prod HPAs work. When I ask for them I see: 

NAME                        REFERENCE                              TARGETS   MINPODS   MAXPODS   REPLICAS   AGE
adjust                      Deployment/adjust                      0%/70%    1         5         1          1d
web-admin                   Deployment/web-admin                   0%/70%    1         3         1          2h

In blue env they don't work, I see: 

NAME                        REFERENCE                              TARGETS   MINPODS   MAXPODS   REPLICAS   AGE
adjust                      Deployment/adjust                      <unknown>/70%    1         5         1          1d
web-admin                   Deployment/web-admin                   <unknown>/70%    1         3         1          2h

in Kubernetes events we see: 

HorizontalPodAutoscaler Warning FailedGetResourceMetric horizontal-pod-autoscaler unable to get metrics for resource cpu: no metrics returned from resource metrics API

Note that the metrics server is running in kube-system, but there are no repo files for that in /third-party" in prod.

In blue we store all metrics-server related files in /thirdpary/metrics-server ( taken from git@github.com:kubernetes-incubator/metrics-server.git )

In prod the deployment has: 

      - command:
        - /metrics-server
        - --source=kubernetes.summary_api:''

In blue this seemed to do the trick 

          - /metrics-server
          - --kubelet-preferred-address-types=InternalIP
          - --kubelet-insecure-tls

Cluster Scaling

ks get configmap cluster-autoscaler-status -o yaml


https://github.com/kubernetes/autoscaler/blob/master/cluster-autoscaler/FAQ.md

Steps to move hardware around

In this case we are removing the last node from an instance group and then removing the instance group.

Reference: https://kubernetes.io/docs/concepts/architecture/nodes/

1. Cordon the node 

k cordon ip-xx-xx-xx-xx.region.compute.internal

No new pods will be deployed here.

2. drain ( move pods here to somewhere else ) 

k drain ip-xx-xx-xx-xx.region.compute.internal

You may need to add "--ignore-daemonsets" if you have daemonsets running ( data dog , localredis )

You may need to "--delete-local-data" if you have a metrics server on this node. BE CAREFUL. You will loose metrics, but probably you have an "out of cluster" place where metrics are stored ( datadog, elastic search, etc )

3. remove the nodegroup from the autoscaler: 

ks edit deploy cluster-autoscaler

4. tell kops to delete the instance group. 

kops delete ig myig

at this point the vms will be shut down. 

k get nodes

Kubeadm way

1. light up some instances:

if you are using amzn linux you can cloud-init like this: 

yum_repos:
    # The name of the repository
    kubernetes:
        # Any repository configuration options
        # See: man yum.conf
        #
        # This one is required!
        baseurl: https://packages.cloud.google.com/yum/repos/kubernetes-el7-x86_64
        enabled: true
        gpgcheck: true
        gpgkey:
         - https://packages.cloud.google.com/yum/doc/yum-key.gpg
         - https://packages.cloud.google.com/yum/doc/rpm-package-key.gpg
        name: kubernetes


packages:
 - curl
 - git 
 - iproute-tc 
 - jq
 - kubeadm
 - kubectl
 - kubelet
 - lsof
 - mlocate
 - ntp 
 - screen
 - strace
 - sysstat
 - tcpdump
 - telnet
 - traceroute
 - tree
 - unzip
 - wget

runcmd:
  - [ /usr/bin/updatedb ]
  - [ 'amazon-linux-extras', 'install', 'docker', '-y' ]
  - [ 'setenforce', '0']
  - [ 'systemctl', 'enable', 'docker']
  - [ 'systemctl', 'start', 'docker' ]
  - [ 'systemctl', 'enable', 'kubelet']
  - [ 'systemctl', 'start', 'kubelet' ]

write_files:
  - content: |
      net.bridge.bridge-nf-call-ip6tables = 1
      net.bridge.bridge-nf-call-iptables = 1
    path: /etc/sysctl.d/k8s.conf
    permissions: '0755'
    owner: root:root
  - content: |
      SERVER=$(/usr/bin/aws ec2 describe-tags --region us-east-1 --filters "Name=resource-id,Values=$(wget -q -O - http://169.254.169.254/latest/meta-data/instance-id)" "Name=key,Values=Name" --query 'Tags[*].Value' --output text)
      PRIVATE_IP=$(curl http://169.254.169.254/latest/meta-data/local-ipv4)
      # if hostname was set this would work, but hostname is not set
      # sed -i "s/^\(HOSTNAME\s*=\s*\).*$/\1$SERVER/" /etc/sysconfig/network
      echo "HOSTNAME=$SERVER" >> /etc/sysconfig/network
      echo "$PRIVATE_IP $SERVER" >> /etc/hosts
      echo "$SERVER" > /etc/hostname
      hostname $SERVER
    path: /root/sethostname.sh
    permissions: '0755'
    owner: root:root

on the first instance, do a 

kubeadm init

and save the output.

run that output on the other instances.

boom! a kubernets cluster...

what is it missing ?

  • your app
  • logging
  • monitoring
  • dashboard

taints

Still learning about this . 

kubectl get nodes -o json | jq .items[].spec.taints

Kubernetes dashboard

get the token for the service account to loggin to the web ui: 

ks get secret `ks get sa kubernetes-dashboard -o=jsonpath='{.secrets[0].name}'` -o=jsonpath='{.data.token}' | base64 -d ; echo

Kubernetes Quiz Links

  1. Pods

https://kodekloud.com/p/practice-test-kubernetes-ckad-pods

  1. ReplicaSets

https://kodekloud.com/p/practice-test-kubernetes-ckad-replicasets

  1. Deployments

https://kodekloud.com/p/practice-test-kubernetes-ckad-deployments

  1. Namespaces

https://kodekloud.com/p/practice-test-kubernetes-ckad-namespaces

  1. Commands and Arguments

https://kodekloud.com/p/practice-test-kubernetes-ckad-commands-and-arguments

  1. ConfigMaps

https://kodekloud.com/p/practice-test-kubernetes-ckad-configmaps

  1. Secrets

https://kodekloud.com/p/practice-test-kubernetes-ckad-secrets

  1. Security Contexts

https://kodekloud.com/p/practice-test-kubernetes-ckad-security-contexts

  1. Service Accounts

https://kodekloud.com/p/practice-test-kubernetes-ckad-service-account

  1. Taints and Tolerations

https://kodekloud.com/p/practice-test-kubernetes-ckad-taints-tolerations

  1. Node Affinity

https://kodekloud.com/p/practice-test-kubernetes-ckad-node-affinity

  1. Multi-Container Pods

https://kodekloud.com/p/practice-test-kubernetes-ckad-multicontainer-pods

  1. Readiness and Liveness Probes

https://kodekloud.com/p/practice-test-kubernetes-ckad-readiness-probes

  1. Container Logging

https://kodekloud.com/p/practice-test-kubernetes-ckad-logging

  1. Monitoring

https://kodekloud.com/p/practice-test-kubernetes-ckad-monitoring

  1. Labels & Selectors

https://kodekloud.com/p/practice-test-kubernetes-ckad-labels-and-selectors

  1. Rolling Updates And Rollbacks

https://kodekloud.com/p/practice-test-kubernetes-ckad-rolling-updates-and-rollbacks

  1. Services

https://kodekloud.com/p/kubernetes-for-beginners-services-493847859


Also See

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