CKA : 2. K8s Core Concepts
Node-Controller monitor each node, with heart-bit every 5 seconds. With grace period of 40 seconds, the controller declared that the node is unreachable. After 5 min, the pods of unhealthy nodes are scheduled on other node.
Kubelet is not deployed by kubeadm
without pod, we need to create network between application container and sidecar container. We need to create volume and share with both containers. We need to monitor both containers.
Pycharm editor has very good support for YAML
- Audo indentation
- at bottom status bar, the format of present line in complete tree of YAML.
- off course syntax color highlighting.
Replicaset has selector. so it will take care of pods created earlier also.
Replica controller does not have selector->mathLabels
Replicaset selector choose from set of value
Replica controller choose pod when key, value matches.
After a pod of RS reached to ImagePullBackOff stage, even if you correct image name at RS.yaml file. no impact. you need to delete all pods of RS. RS will create new pod using correct image.
In the RS, these two values should be identical
spec->selector->matchLabels
spec->template->metadata-labels
RS and deployment has same YAML file. Deployment creates RS and RS creates pod.
To change namespace in kubectl the command is:
k config set-context $(k config current-context) --namespace=dev
ResourceQuota is for namespace.
Deployment should be created with "k create deployment" command then set replica count with "k scale" command.
Scheduler consider following values from YAML
- affinity / anti-affinity
- nodeSelector
- taints / tolerations
- reservations / limits
Kubelet is not deployed by kubeadm
without pod, we need to create network between application container and sidecar container. We need to create volume and share with both containers. We need to monitor both containers.
Pycharm editor has very good support for YAML
- Audo indentation
- at bottom status bar, the format of present line in complete tree of YAML.
- off course syntax color highlighting.
Replicaset has selector. so it will take care of pods created earlier also.
Replica controller does not have selector->mathLabels
Replicaset selector choose from set of value
Replica controller choose pod when key, value matches.
After a pod of RS reached to ImagePullBackOff stage, even if you correct image name at RS.yaml file. no impact. you need to delete all pods of RS. RS will create new pod using correct image.
In the RS, these two values should be identical
spec->selector->matchLabels
spec->template->metadata-labels
RS and deployment has same YAML file. Deployment creates RS and RS creates pod.
To change namespace in kubectl the command is:
k config set-context $(k config current-context) --namespace=dev
ResourceQuota is for namespace.
Deployment should be created with "k create deployment" command then set replica count with "k scale" command.
Scheduler consider following values from YAML
- affinity / anti-affinity
- nodeSelector
- taints / tolerations
- reservations / limits
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