Kubernetes Pods

Introduction 
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* group of 1 or more containers 

* pod names are also DNS names within kubernetes clusters 

  format of pod name: <replica-set name>-<hash> 

 

Sample Manifests 

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Basic
Specifying node selection	apiVersion: v1  kind: Pod  metadata:    name: cuda-test  spec:    containers:      - name: cuda-test        image: "k8s.gcr.io/cuda-vector-add:v0.1"        resources:          limits:            nvidia.com/gpu: 1    nodeSelector:      accelerator: nvidia-tesla-p100

 

Tutorials 

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Listing pod names	kubectl get pods --selector=job-name=pi --output=jsonpath='{.items[*].metadata.name}'
Basic Pod	apiVersion: v1  kind: Pod  metadata:    name: myapp-pod    labels:    app: myapp  spec:    containers:    - name: myapp-container      image: busybox      command: ['sh', '-c', 'echo Hello Kubernetes! && sleep 3600']    Using local host path as volume mounts    apiVersion: v1  kind: Pod  metadata:    name: ftp  spec:    containers:    - name: logstash      image: myfiles:v1      ports:      - containerPort: 21        name: ftp      volumeMounts:      - name: ftp        mountPath: /var/ftp/pub    volumes:    - name: ftp      hostPath:        path: /home/john/local/ftp_files
Defining environment  variable for a container	apiVersion: v1  kind: Pod  metadata:    name: envar-demo    labels:    purpose: demonstrate-envars  spec:    containers:    - name: envar-demo-container      image: gcr.io/google-samples/node-hello:1.0      env:      - name: DEMO_GREETING        value: "Hello from the environment"      - name: DEMO_FAREWELL        value: "Such a sweet sorrow"
Using initcontainer	apiVersion: v1  kind: Pod  metadata:    name: myapp-pod    labels:    app: myapp  spec:    containers:    - name: myapp-container      image: busybox      command: ['sh', '-c', 'echo The app is running! && sleep 3600']    initContainers:    - name: init-myservice      image: busybox      command: ['sh', '-c', 'until nslookup myservice; do echo waiting for myservice; sleep 2; done;']    - name: init-mydb      image: busybox      command: ['sh', '-c', 'until nslookup mydb; do echo waiting for mydb; sleep 2; done;']
Using emtyDir as volume	apiVersion: v1  kind: Pod  metadata:    name: test-pd  spec:    containers:    - image: k8s.gcr.io/test-webserver      name: test-container      volumeMounts:      - mountPath: /cache        name: cache-volume    volumes:    - name: cache-volume      emptyDir: {}
Exposing UDP port	[...]  spec:    containers:    - name: logstash      image: myfiles:v1      ports:      - containerPort: 514        protocol: UDP        name: syslog  [...]
Running container  as different user	apiVersion: v1  kind: Pod  metadata:    name: security-context-demo  spec:    securityContext:    runAsUser: 1000    fsGroup: 2000    volumes:    - name: sec-ctx-vol        emptyDir: {}    containers:    - name: sec-ctx-demo      image: gcr.io/google-samples/node-hello:1.0  [...]
Adding arguments	- name: logstash          image: docker.elastic.co/logstash/logstash-oss:6.2.3          args:          - "--pipeline.batch.size=500"
Executing commands on pod startup and shutdown	apiVersion: v1  kind: Pod  metadata:    name: lifecycle-demo  spec:    containers:    - name: lifecycle-demo-container      image: nginx      lifecycle:        postStart: # --> no guarantee that this will be executed before container's entrypoint          exec:            command: ["/bin/sh", "-c", "echo Hello from the postStart handler > /usr/share/message"]        preStop:          exec:            command: ["/usr/sbin/nginx","-s","quit"]
Adding resource requests/limit	[...]          volumeMounts:          - name: mariadbdata            mountPath: /var/lib/mysql          ports:            - containerPort: 3306              name: mariadb          resources:            requests:              cpu: 1              memory: 2Gi            limits:              cpu: 2              memory: 4Gi        volumes:  [...]    https://kubernetes.io/docs/concepts/configuration/manage-compute-resources-container/#resource-requests-and-limits-of-pod-and-container
Adding hostAliases on pods	apiVersion: v1  kind: Pod  metadata:    name: hostaliases-pod  spec:    restartPolicy: Never    hostAliases:    - ip: "127.0.0.1"      hostnames:      - "foo.local"      - "bar.local"    - ip: "10.1.2.3"      hostnames:      - "foo.remote"      - "bar.remote"    containers:    - name: cat-hosts      image: busybox      command:      - cat      args:      - "/etc/hosts"
Adding command and arguments	apiVersion: v1  kind: Pod  metadata:    name: command-demo    labels:      purpose: demonstrate-command  spec:    containers:    - name: command-demo-container      image: debian      command: ["printenv"]      args: ["HOSTNAME", "KUBERNETES_PORT"]    restartPolicy: OnFailure
Get only pod names	kubectl get pods --template '{{range .items}}{{.metadata.name}}{{"\n"}}{{end}}'  kubectl get po -o name
Delete all pods in a namespace	kubectl -n namespace_name delete po `kubectl get pods -o go-template --template '{{range .items}}{{.metadata.name}}{{"\n"}}{{end}}'`
Running as specific user	spec:    securityContext:      runAsUser: 1000    containers:    [...]