Key Kubernetes Concepts
Kubernetes is a powerful container orchestration platform that automates deployment, scaling, and operations of containerised applications. Understanding its key concepts is essential for effectively managing modern cloud-native applications. Here are 15 of the most common Kubernetes concepts:
1. Cluster
A Kubernetes cluster is the foundation of the system, consisting of multiple nodes (machines) that work together to run applications. It includes a control plane that manages the cluster and worker nodes that execute workloads.
2. Node
A node is an individual machine (physical or virtual) in the cluster that runs containerised applications. Nodes include essential components such as a container runtime, kubelet, and networking capabilities.
3. Pod
The smallest deployable unit in Kubernetes, a pod encapsulates one or more tightly coupled containers that share networking and storage resources. Pods ensure that containers communicate efficiently and are scheduled together.
4. Deployment
A deployment defines how applications are managed, enabling automated rollouts, updates, and scaling. It ensures that the desired number of pods are running and can roll back changes if necessary.
5. ReplicaSet
A ReplicaSet maintains a specified number of identical pod instances, ensuring high availability and resilience. Deployments typically use ReplicaSets to manage pod scaling.
6. Service
A service abstracts and exposes a stable endpoint to connect applications, allowing communication between pods or external users. It provides load balancing and ensures that traffic reaches healthy pods.
7. Ingress
Ingress is a Kubernetes resource that manages external access to services, typically via HTTP or HTTPS. It allows for path-based routing, SSL termination, and traffic management.
8. ConfigMap
ConfigMaps store non-sensitive configuration data, such as environment variables and application settings, allowing configuration to be managed separately from application code.
9. Secret
Secrets store sensitive data, such as API keys, passwords, and tokens, securely within the cluster, preventing exposure in application code.
10. Namespace
Namespaces provide logical separation within a cluster, enabling multi-tenancy, resource allocation, and isolation for different teams or applications.
11. Persistent Volume (PV) & Persistent Volume Claim (PVC)
- Persistent Volumes (PV): Storage resources that exist independently of pods, enabling persistent data storage.
- Persistent Volume Claims (PVC): Requests for storage resources by applications, dynamically provisioning storage as needed.
12. StatefulSet
StatefulSets manage stateful applications that require stable, unique network identities and persistent storage, such as databases.
13. DaemonSet
A DaemonSet ensures that a copy of a specific pod runs on all (or some) nodes, commonly used for logging, monitoring, and networking functions.
14. Job & CronJob
- Job: Executes a task to completion, ensuring successful execution of batch processing tasks.
- CronJob: Runs scheduled tasks at specific intervals, similar to traditional cron jobs.
15. Horizontal & Vertical Pod Autoscaling (HPA & VPA)
- Horizontal Pod Autoscaler (HPA): Automatically scales the number of pods based on CPU/memory usage or custom metrics.
- Vertical Pod Autoscaler (VPA): Dynamically adjusts resource requests and limits for individual pods.
These concepts form the backbone of Kubernetes, enabling efficient container orchestration, scalability, and automation in modern cloud environments.