readme.md

CKA Exam Quick Pointers

Table of Contents

1. Kubernetes Important Components
2. Important Kubernetes Directories
3. Kubernetes Important Commands
4. Kubectl Output Customization
5. Important Vim Commands
6. Important Grep Options
7. Important Systemd Commands

Kubernetes Important Components:

• API Server

  • Port: 6443
  • Description: Serves the Kubernetes API and is the central management entity for the cluster's operations and communications.

• etcd

  • Ports: 2379 (client requests), 2380 (peer communication)
  • Description: Key-value store for all cluster data, acting as Kubernetes' backing store for all cluster state and data.

• Scheduler

  • Description: Watches for newly created Pods with no assigned node and selects a node for them to run on.

• Controller Manager

  • Port: 10252
  • Description: Runs controller processes such as node controller, endpoints controller, and namespace controller.

• Kubelet

  • Port: 10250
  • Description: Agent running on each node, ensuring containers are running in a Pod as intended.

  Kube-proxy

  • Description: Manages network rules on nodes to allow network communication to Pods.

Important Kubernetes Directories

~/.kube/config

• Path: ~/.kube/config
• Description: This is the default location for a user's kubeconfig file, which stores the cluster connection and access information. It allows kubectl and other Kubernetes client tools to communicate with the Kubernetes cluster. The file contains details such as cluster definitions, user credentials, and context for switching between clusters.
• Management:
  • Use kubectl config commands to view, modify, and manage your kubeconfig settings.
  • Merge multiple kubeconfig files by setting the KUBECONFIG environment variable to a list of file paths to aggregate configuration from those files.

/etc/kubernetes/

• Description: The main configuration directory for Kubernetes components.
• Key Subdirectories:
  • /etc/kubernetes/manifests/: Contains static pod manifests for starting control plane components as static pods.
  • /etc/kubernetes/pki/: Stores the Certificate Authority (CA) and other TLS certificates for securing cluster communication.

/var/lib/kubelet/

• Description: The primary directory used by the kubelet.
• Key Subdirectories:
  • /var/lib/kubelet/pods/: Data about pods managed by the kubelet, including volumes and configuration.
  • /var/lib/kubelet/pki/: Contains the kubelet's private key and certificate.

/var/lib/etcd/

• Description: Default directory for etcd data storage.
• Key Points: Contains the etcd database with all Kubernetes cluster state.

/var/log/

• Description: Contains log files for Kubernetes components and the container runtime.
• Key Subdirectories:
  • /var/log/kube-apiserver.log: Logs from the Kubernetes API server.
  • /var/log/kube-scheduler.log: Logs from the Kubernetes scheduler.
  • /var/log/kube-controller-manager.log: Logs from the Kubernetes controller manager.
  • /var/log/kubelet.log: Logs from the kubelet service.
  • /var/log/containers/: Logs for containers managed by Kubernetes.

/etc/cni/net.d/

• Description: Where CNI plugin configurations are stored.

Kubernetes Important Commands

Resource Management

Command	Description	Example Usage
create	Create a resource from a file or from stdin.	kubectl create -f <config-file>
delete	Delete resources by names, file, or types.	kubectl delete pod <pod-name>
apply	Apply a configuration change to a resource from a file.	kubectl apply -f <config-file>
replace	Replace a resource by filename or stdin.	kubectl replace -f <config-file>
patch	Update field(s) of a resource.	kubectl patch deployment <name> -p '{"spec":{"replicas":5}}'
edit	Edit the specified resource with the default editor.	kubectl edit deployment/<deployment-name>

Resource Inspection and Debugging

Command	Description	Example Usage
get	List resources.	kubectl get <resource-name>
describe	Show detailed information about a specific resource.	kubectl describe <resource-type>/<resource-name>
logs	Print the logs for a container in a pod.	kubectl logs <pod-name>
exec	Execute a command inside a container in a pod.	kubectl exec -it <pod-name> -- /bin/bash
top	Display resource (CPU/Memory/Storage) usage.	kubectl top nodes

Configuration and Security

Command	Description	Example Usage
config set-context	Change the current context's namespace or user.	kubectl config set-context --current --namespace=<namespace>
config get-contexts	Display list of contexts.	kubectl config get-contexts
config use-context	Switch to use a different context.	kubectl config use-context <context-name>
config view	Show merged kubeconfig settings.	kubectl config view
config set-credentials	Set a user entry in kubeconfig.	kubectl config set-credentials <user-name> --token=<token>
auth can-i	Check whether the current user can perform a given action.	kubectl auth can-i create deployments

Deployment Management

Command	Description	Example Usage
scale	Scale a deployment to a specified number of replicas.	kubectl scale deployment/<name> --replicas=<num>
expose	Expose a pod, deployment, or service as a new Kubernetes service.	kubectl expose deployment/<name> --type=LoadBalancer --port=8080
rollout status	Show the rollout status of a deployment.	kubectl rollout status deployment/<name>
rollout restart	Restart a deployment.	kubectl rollout restart deployment/<name>
set image	Update the image of a container of a pod or selected set of pods.	kubectl set image deployment/<name> <container>=<image>

Node Management

Command	Description	Example Usage
cordon	Mark a node as unschedulable.	kubectl cordon <node-name>
uncordon	Mark a node as schedulable.	kubectl uncordon <node-name>
drain	Prepare a node for maintenance, evicting pods gracefully.	kubectl drain <node-name> --ignore-daemonsets
taint	Update the taints on a node.	kubectl taint nodes <node-name> key=value:NoSchedule

Kubectl Output Customization

Output Type	Specific Example
Custom Columns	kubectl get pods -o=custom-columns=NAME:.metadata.name,STATUS:.status.phase --sort-by=.metadata.creationTimestamp
JSON Path	kubectl config view --kubeconfig=my-kube-config -o jsonpath="{.contexts[?(@.context.user=='aws-user')].name}"

Important Vim Commands

Command	Description
i	Enter insert mode before the current cursor position.
a	Enter insert mode after the current cursor position.
v	Enter visual mode (character selection).
V	Enter visual line mode (line selection).
Ctrl + v	Enter visual block mode (block selection).
:w	Save the file but don't exit Vim.
:wq or :x	Save the file and exit Vim.
:q	Quit Vim (fails if there are unsaved changes).
:q!	Quit Vim and discard any changes.
dd	Delete the current line (cut).
yy	Yank (copy) the current line.
p	Paste the clipboard content after the cursor.
P	Paste the clipboard content before the cursor.
u	Undo the last operation.
Ctrl + r	Redo the last undone operation.
/	Search forward for a pattern.
?	Search backward for a pattern.
n	Repeat the last search in the same direction.
N	Repeat the last search in the opposite direction.
:%s/old/new/g	Replace all occurrences of old with new throughout the file. Any delimiter can be used, e.g., :%s#old#new#g.
:noh	Remove search highlighting.
gg	Go to the first line of the document.
G	Go to the last line of the document.
:set nu	Turn on line numbering.
:set nonu	Turn off line numbering.

Important Grep Options

Option	Description
-i	Ignore case distinctions in both the pattern and input files.
-v	Invert the sense of matching, to select non-matching lines.
-r	Recursively search subdirectories listed.
-n	Print the line number of each matching line.
--color=auto	Highlight matching strings. Automatically shows colors when outputting to terminal.
-A <number>	Print <number> lines of trailing context after matching lines.
-B <number>	Print <number> lines of leading context before matching lines.

Important Systemd Commands

Command	Description
systemctl daemon-reload	Reloads the systemd manager configuration to read any changes.
systemctl start <service>	Starts a specific service.
systemctl stop <service>	Stops a specific service.
systemctl restart <service>	Restarts a specific service.
systemctl status <service>	Displays the status of a specific service.
systemctl enable <service>	Enables a service to start at boot.
systemctl disable <service>	Disables a service from starting at boot.
systemctl is-enabled <service>	Checks if a service is enabled to start on boot.
systemctl is-active <service>	Checks if a service is currently active.
systemctl list-units --type=service --state=running	Lists all running units of type service.
journalctl -u <service>	Displays the journal logs for a specific service.
journalctl -f	Tails the journal logs in real-time.

Note: In the commands above, <service> can be specified with or without the .service suffix (e.g., kubelet or kubelet.service). Including .service is optional and used for more clarity, especially in scripts or when different unit types with the same name exist.