Kubernetes.md

Kubernetes

Kubernetes Architecture Overview

                   +--------------------+
                   |   Control Plane    |
                   |   (Master Node)    |
                   +--------------------+
                   |  API Server        |
                   |  Scheduler         |
                   |  Controller Manager|
                   |  etcd (key store)  |
                   +--------------------+
                            |
        -----------------------------------------------
        |                       |                     |
+----------------+   +----------------+       +----------------+
|  Worker Node 1 |   | Worker Node 2  |       |  Worker Node N |
+----------------+   +----------------+       +----------------+
| kubelet        |   | kubelet        |       | kubelet        |
| kube-proxy     |   | kube-proxy     |       | kube-proxy     |
| container runtime| | container runtime|     | container runtime|
| Pods            |  | Pods           |       | Pods            |
+----------------+   +----------------+       +----------------+

Required Components

• cluster - one or more worker machine
• node - one worker machine/virtual machine
• Namespace - folder or workspace for each node
• pods - running applications

Cluster Info

kubectl version                         # Version of kubectl and Kubernetes server
kubectl cluster-info                    # Info about cluster endpoints
kubectl get nodes                       # List all nodes
kubectl describe node <node-name>       # Detailed info about a node ( if node is down )

Namespaces Info

kubectl get ns                         # List namespaces(autobaml/pyora)
kubectl create namespace <name>        # Create new namespace
kubectl delete namespace <name>        # Delete namespace

Pods Info

kubectl get pods                       # List all pods
kubectl get pods -A                    # List pods in all namespaces
kubectl get pods -n <namespace>        # List pods in a namespace
kubectl describe pod <pod-name>        # Details of a specific pod
kubectl logs <pod-name>                # View logs of a pod
kubectl logs <pod-name> -c <container> # Logs for specific container in pod
kubectl exec -it <pod-name> -- /bin/bash  # SSH into a pod
kubectl delete pod <pod-name>          # Delete a pod

NOTE: If our pods are running within a specific namespace, we'll need to use the -n flag with kubectl to target that namespace. Example: To get pods in the payments namespace:

```bash
kubectl get pods -n payments
```
Using Shell Alias
we can create an alias in our .bashrc, .zshrc, or shell configuration file to make this easier:
```bash
alias pay='kubectl -n payments'
```
After reloading our shell (or sourcing the file), you can simply run:
```bash
pay get pods
```
List All Aliases
To list all defined aliases in your shell:
```bash
alias
```

relation diagram of Kubernetes Deployment, ConfigMap, and Service

                         +----------------+
                         |  ConfigMap     |
                         | (app settings) |
                         +-------+--------+
                                 |
                                 |
                      mounted / injected into
                                 |
                         +-------v--------+
                         | Deployment     |
                         | (manages Pods) |
                         +-------+--------+
                                 |
                  creates        |     uses
               +-----------------v----------------+
               |             Pod                  |
               |  (includes app containers)       |
               +--------+--------------+----------+
                        |              |
                uses env/config   exposes port
                        |              |
                        +--------------v-------------+
                                       |
                                +------+------------+
                                |   Service         |
                                | (load balancer)   |
                                +-------------------+

Deployments & Services

kubectl get deployments                 # List deployments
kubectl describe deployment <name>     # Deployment details
kubectl create deployment nginx --image=nginx  # Create a deployment
kubectl scale deployment nginx --replicas=3    # Scale deployment
kubectl delete deployment <name>       # Delete deployment

kubectl get svc                         # List services
kubectl expose deployment nginx --port=80 --type=NodePort  # Expose deployment

ConfigMaps & Secrets

kubectl get configmaps                 # List ConfigMaps
kubectl describe configmap <name>      # Show ConfigMap data
kubectl get secrets                    # List secrets
kubectl describe secret <name>         # View secret metadata
kubectl create secret generic my-secret --from-literal=key1=val1

Events & Debugging

kubectl get events                     # Get recent events
kubectl describe pod <pod-name>        # View pod issues
kubectl top pod                        # Show pod resource usage
kubectl top node                       # Show node resource usage

Resource Exploration

kubectl api-resources                  # All available resources
kubectl explain pod                    # Show pod definition and fields

Endpoint ( db ip is defined here )

• When you create a Service, Kubernetes automatically creates an associated Endpoint object.
• This Endpoint stores a list of IP addresses (and ports) for the Pods that match the Service’s selector.
• So, the Service routes traffic to the IPs listed in its Endpoints.

kubectl get endpoints

Service vs Endpoint in Kubernetes

Feature	Service	Endpoint
What it is	An abstraction to expose a set of Pods	A list of actual Pod IPs behind the Service
Type	Kubernetes resource (Service)	Kubernetes resource (Endpoints)
Created by	You, as a user (kubectl apply, YAML)	Automatically by Kubernetes when a Service is created
Purpose	Load balances and routes traffic	Keeps track of Pod IPs the Service can send traffic to
Stable?	Yes — has a stable virtual IP and DNS name	No — Pod IPs can change as pods restart/scale
Visible with	kubectl get svc	kubectl get endpoints
Works With	ClusterIP, NodePort, LoadBalancer, Headless	Headless or regular services

Service Mesh ( pending write up ... )