Kubernetes basics review in Microservices - Architecture Diagram

System Overview - Kubernetes basics review

Kubernetes is a system that helps run and manage many small programs called containers. It makes sure these containers work well together, can grow when needed, and recover if something breaks.

Architecture Diagram

User
  |
  v
+----------------+
|  kubectl CLI   |
+----------------+
        |
        v
+----------------+
| Kubernetes API |
|    Server      |
+----------------+
        |
        v
+----------------+       +----------------+       +----------------+
|  Scheduler     |<----->| Controller     |<----->| etcd (Storage) |
| (assign pods)  |       | Manager        |       +----------------+
+----------------+       +----------------+
        |
        v
+----------------+       +----------------+
|  Node (Worker) |<----->| Kubelet Agent  |
|  (runs pods)   |       +----------------+
+----------------+
        |
        v
+----------------+
|  Container(s)  |
+----------------+

Components

User

user

Person who interacts with the Kubernetes cluster

kubectl CLI

client

Command line tool to send requests to Kubernetes API

Kubernetes API Server

api_gateway

Receives and processes all requests to the cluster

Scheduler

service

Decides which node will run each container

Controller Manager

service

Maintains cluster state and manages controllers

etcd

database

Stores all cluster data and configuration

Node (Worker)

compute_node

Physical or virtual machine that runs containers

Kubelet Agent

agent

Runs on each node to manage containers and report status

Container(s)

container

Small programs running inside nodes

Request Flow - 10 Hops

User → kubectl CLI

kubectl CLI → Kubernetes API Server

Kubernetes API Server → etcd

Scheduler → Node (Worker)

Kubernetes API Server → Controller Manager

Controller Manager → Kubelet Agent

Kubelet Agent → Container(s)

Container(s) → Kubelet Agent

Kubelet Agent → Kubernetes API Server

Kubernetes API Server → User

Failure Scenario

Component Fails:etcd

Impact:Cluster cannot store or retrieve state data, causing scheduling and management failures

Mitigation:Use etcd replication and backups to restore state; cluster continues running with last known state but cannot update

Architecture Quiz - 3 Questions

Which component decides where containers run in the cluster?

A Scheduler

B Kubelet Agent

C Controller Manager

D etcd

Design Principle

Kubernetes architecture separates concerns: API Server handles requests, Scheduler assigns workloads, Controller Manager maintains state, and Kubelet manages containers on nodes. This modular design enables scalability, fault tolerance, and clear responsibility boundaries.

Practice

1. What is a pod in Kubernetes?

easy

A. A command-line tool to manage Kubernetes

B. The smallest unit that runs one or more containers together

C. A configuration file format used in Kubernetes

D. A network policy to control traffic

Solution

1. Step 1: Understand Kubernetes resource types

   Kubernetes groups containers into pods to run them together on the same host.

2. Step 2: Identify the role of a pod

   A pod is the smallest deployable unit that can contain one or more containers sharing resources.

3. Final Answer:

   The smallest unit that runs one or more containers together -> Option B

4. Quick Check:

   Pod = smallest container group [OK]

Hint: Pods group containers; smallest deployable unit [OK]

Common Mistakes:

• Confusing pods with kubectl tool
• Thinking pods are config files
• Mixing pods with network policies

2. Which command correctly lists all pods in the default namespace?

easy

A. kubectl get pods

B. kubectl list pods

C. kubectl show pods

D. kubectl describe pods all

Solution

1. Step 1: Recall kubectl commands for listing resources

   The standard command to list pods is kubectl get pods.

2. Step 2: Check other options for correctness

   kubectl list pods and kubectl show pods are invalid commands; kubectl describe pods all is incorrect syntax.

3. Final Answer:

   kubectl get pods -> Option A

4. Quick Check:

   List pods = kubectl get pods [OK]

Hint: Use 'kubectl get pods' to list pods [OK]

Common Mistakes:

• Using 'list' or 'show' instead of 'get'
• Adding unnecessary arguments like 'all'
• Confusing describe with get

3. Given this YAML snippet for a pod:

apiVersion: v1
kind: Pod
metadata:
  name: myapp-pod
spec:
  containers:
  - name: myapp-container
    image: nginx:latest
    ports:
    - containerPort: 80

What will kubectl get pods myapp-pod show after creation?

medium

A. NAME READY STATUS RESTARTS AGE
myapp-pod 1/1 Completed 0 0s

B. Error: pod not found

C. NAME READY STATUS RESTARTS AGE
myapp-pod 0/1 Pending 0 0s

D. NAME READY STATUS RESTARTS AGE
myapp-pod 1/1 Running 0 0s

Solution

1. Step 1: Understand pod creation from YAML

   The YAML defines a pod with one container running nginx, exposing port 80.

2. Step 2: Predict pod status after creation

   Immediately after creation, the pod should be running with 1 container ready, so status is Running and READY is 1/1.

3. Final Answer:

   NAME READY STATUS RESTARTS AGE myapp-pod 1/1 Running 0 0s -> Option D

4. Quick Check:

   Pod created and running = READY 1/1 Running [OK]

Hint: New pod with valid image shows READY 1/1 Running [OK]

Common Mistakes:

• Expecting Pending status without reason
• Confusing Completed with Running
• Assuming pod not found immediately after creation

4. You run kubectl apply -f pod.yaml but get an error: "error: unable to recognize \"pod.yaml\": no matches for kind \"Pod\" in version \"v2\"". What is the likely fix?

medium

A. Delete the pod.yaml and recreate it

B. Rename the file to pod.yml

C. Change apiVersion from v2 to v1 in pod.yaml

D. Run the command with sudo

Solution

1. Step 1: Analyze the error message

   The error says no matches for kind "Pod" in version "v2", meaning the apiVersion is invalid.

2. Step 2: Correct the apiVersion in YAML

   The correct apiVersion for Pod is "v1", so changing from "v2" to "v1" fixes the issue.

3. Final Answer:

   Change apiVersion from v2 to v1 in pod.yaml -> Option C

4. Quick Check:

   apiVersion must be valid (v1 for Pod) [OK]

Hint: Check apiVersion spelling and value in YAML [OK]

Common Mistakes:

• Changing file extension instead of apiVersion
• Running with sudo unnecessarily
• Deleting file without fixing content

5. You want to update a running pod's container image from nginx:1.19 to nginx:1.21 without downtime. Which Kubernetes resource and method should you use?

hard

A. Create a Deployment and update its image with kubectl set image

B. Directly edit the pod with kubectl edit pod to change the image

C. Delete the pod and create a new one with the new image

D. Use kubectl scale pod to increase replicas

Solution

1. Step 1: Understand pod immutability and updates

   Pods are immutable; you cannot update container images directly on running pods without recreating them.

2. Step 2: Use Deployment for zero downtime updates

   Deployments manage pods and allow rolling updates to change images without downtime using kubectl set image.

3. Final Answer:

   Create a Deployment and update its image with kubectl set image -> Option A

4. Quick Check:

   Use Deployment + set image for smooth updates [OK]

Hint: Use Deployment and set image for zero downtime update [OK]

Common Mistakes:

• Trying to edit pod image directly
• Deleting pod causes downtime
• Scaling pod is invalid command