Kubernetes (CKA/CKAD) - Container Orchestration & Cluster Architecture Flashcards

Question 1

Control Plane Components

Accepted Answer

The master components managing the cluster state:
- `kube-apiserver`: Exposes the Kubernetes API (gateway).
- `etcd`: Consistent, highly-available key-value store for cluster data.
- `kube-scheduler`: Assigns newly created Pods to Nodes based on resource requirements.
- `kube-controller-manager`: Runs controller processes (e.g., NodeController, ReplicaSetController).

Question 2

Worker Node Components

Accepted Answer

Components running on every worker node to maintain running Pods:
- `kubelet`: Primary node agent ensuring containers defined in PodSpecs are running and healthy.
- `kube-proxy`: Maintains network rules on nodes to allow network communication to Pods.
- **Container Runtime**: Software responsible for running containers (e.g., `containerd`, CRI-O).

Question 3

Pod

Accepted Answer

The smallest deployable computing unit in Kubernetes. Represents a single instance of a running process in a cluster, containing one or more co-located containers that share network namespaces, storage volumes, and IP addresses.

Question 4

Deployment vs. ReplicaSet

Accepted Answer

- **ReplicaSet**: Ensures a specified number of identical Pod replicas are running at any given time.
- **Deployment**: A higher-level declarative object that manages ReplicaSets, enabling automated rolling updates, rollbacks, and pause/resume capabilities for application versions.

Question 5

DaemonSet

Accepted Answer

A workload API object ensuring that all (or matching) Nodes run a copy of a specific Pod. Automatically schedules Pods onto newly added nodes. Common use cases include cluster logging (e.g., `fluentd`), monitoring agents (e.g., `prometheus-node-exporter`), and network plugins.

Question 6

StatefulSet

Accepted Answer

Manages stateful applications requiring unique network identifiers, persistent storage, and ordered creation/deletion/scaling. Pods are given sticky identities (`pod-name-0`, `pod-name-1`) and dedicated PVs via `volumeClaimTemplates`. Ideal for databases like PostgreSQL and ZooKeeper.

Question 7

Service Types: ClusterIP vs. NodePort vs. LoadBalancer

Accepted Answer

- `ClusterIP`: Exposes Service on an internal IP within the cluster (default).
- `NodePort`: Exposes Service on each Node's IP at a static port (`30000-32767`).
- `LoadBalancer`: Creates an external load balancer using a cloud provider's API and assigns a public IP to the Service.

Question 8

Headless Service

Accepted Answer

A Service defined with `spec.clusterIP: None`. Instead of load balancing traffic via a single IP, DNS queries return the individual A/AAAA records of backing Pods. Essential for discovery in StatefulSets.

Question 9

Ingress & Ingress Controller

Accepted Answer

- **Ingress**: An API object defining HTTP/HTTPS routing rules (hostnames, paths, SSL/TLS termination) to expose cluster Services externally.
- **Ingress Controller**: The actual application (e.g., NGINX, Traefik) that processes Ingress rules and proxies incoming traffic.

Question 10

NetworkPolicy

Accepted Answer

An API object configuring layer 3 and layer 4 traffic isolation rules for Pods. By default, Pod network traffic is non-isolated (`allow-all`). Applying a `NetworkPolicy` switches Pods to an implicit `deny-all` for unmatched ingress/egress traffic.

Question 11

PersistentVolume (PV) vs. PersistentVolumeClaim (PVC)

Accepted Answer

- **PV**: A piece of storage provisioned in the cluster manually by an admin or dynamically via a `StorageClass`.
- **PVC**: A request for storage by a user/Pod specifying size, access modes (`ReadWriteOnce`, `ReadOnlyMany`, `ReadWriteMany`), and optional `StorageClass` requirements.

Question 12

StorageClass & Dynamic Provisioning

Accepted Answer

A `StorageClass` defines parameters for dynamic storage provisioning (e.g., volume type, provisioner like AWS EBS or NFS). When a `PVC` requests a specific `StorageClass`, Kubernetes automatically provisions a matching `PV` on-demand.

Question 13

ConfigMap vs. Secret

Accepted Answer

- **ConfigMap**: Stores non-confidential configuration key-value pairs consumed as environment variables, CLI arguments, or volume mounts.
- **Secret**: Stores sensitive data (passwords, TLS keys) encoded in `base64` to prevent exposure in raw manifests and restricted via RBAC.

Question 14

Liveness, Readiness, and Startup Probes

Accepted Answer

- **Liveness Probe**: Checks if container is alive. If failed, `kubelet` restarts the container.
- **Readiness Probe**: Checks if container is ready to process traffic. If failed, the Pod IP is removed from Service endpoints.
- **Startup Probe**: Disables Liveness/Readiness probes until slow-starting applications finish initial boot.

Question 15

Node Affinity vs. Taints & Tolerations

Accepted Answer

- **Node Affinity**: Attracts Pods to specific Nodes using labels (e.g., `disktype=ssd`).
- **Taints & Tolerations**: Taints are applied to Nodes to repel Pods unless a Pod explicitly includes a matching `Toleration` (used to dedicate nodes to specific workloads).

Question 16

Imperative Pod Creation Command

Accepted Answer

Create and run a single Pod using `kubectl`:
`kubectl run nginx-pod --image=nginx:alpine --port=80 -n default`

Question 17

Generating Resource YAML Manifests

Accepted Answer

Generate a template manifest file without creating the resource on the cluster using `--dry-run=client`:
`kubectl create deployment my-deploy --image=nginx --dry-run=client -o yaml > deploy.yaml`

Question 18

Imperative Service Exposure Command

Accepted Answer

Expose an existing Deployment as a NodePort Service:
`kubectl expose deployment my-deploy --name=my-service --type=NodePort --port=80 --target-port=8080`

Question 19

Deployment Rolling Update & Rollback

Accepted Answer

Update deployment container image:
`kubectl set image deployment/my-deploy nginx=nginx:1.25`

Check status or perform a rollback:
`kubectl rollout status deployment/my-deploy`  
`kubectl rollout undo deployment/my-deploy`

Question 20

Debugging Pods with kubectl

Accepted Answer

Fetch container logs: `kubectl logs -c --tail=50 -f` Execute an interactive command inside a container: `kubectl exec -it -- /bin/sh`

Kubernetes (CKA/CKAD) - Container Orchestration & Cluster Architecture

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