Kubernetes 1 Flashcards
What is Kubernetes?
A Container Orchestration System.
- Its open source.
- Purpose is to automate the deployment, scaling and operation of containers.
- It runs on data center servers.
What is an Orchestration Software/What does it do?
Sits on top of a data center hardware.
Provides:
- Deployment of applications on the data center.
- Scaling of applications resources in response to demand.
- Restarts applications that have crashed (Self-Healing).
- Zero-downtime updates and rollbacks.
What are Kubernetes Clusters?
Nodes (Machines), that run containerised applications.
- Machines can be physical or virtual.
What type of Nodes are there?
Two types:
Controle plane Nodes
Worker Nodes
What is the Control Plane Nodes responsible for?
Managing the cluster.
What are Worker Nodes responsible for?
Running the Containers
What are the components of the Controle Plane?
API Server - Front end of Kubernetes control plane
Cluster Store - key value store
Scheduler - schedules work to be done
Controllers - handles routine tasks in a cluster
Controller Manager - manages the controllers
What is the API Server in Kubernetes?
Acts as a front end for the kubernates control plane
Exposes RESTful API over HTTPS
What is the Cluster Store in Kubernetes?
Key-Value Store that holds the state of the cluster.
Holds information about Kubernetes objects such as;
- Pods
- Services
- Deployments
Designed to be distributed and replaced to ensure high availability and prevent data loss
Most common cluster store in Kubernetes is etcd
What are Controllers in Kubernetes?
Controllers performe task of watching the state of the clustor and making changes to the clustor.
Main Controllers:
- Deployment Controller
- StatefulSet Controller
- ReplicaSet Controller
What is the Controller Manager in kubernates?
Manages the controllers
What is the Schedulder of the Control plane?
Watches the API server for new tasks and selects a node for them to run on.
Decision is based on:
- Resource requirement of the task
- Resources available on each node
- any constraints specified
If there is no node that meets these requirements, Task will remain pending until there is one that meets the requirement.
Pending tasks can trigger automatic increase in the number of nodes in the cluster
What do Worker nodes do in a kubernates cluster?
Handels execution of containers.
Each Worker node has the components:
- Kubelet - runs on each worker node and manages lifecycle of containers
- One or more container runtimes - to run containers
- Apkube Proxy - provides networking
What are the components of a worker node?
- Kubelet
- At least one container runtimes
- Apkube Proxy
What are Kubelets? What does it do?
An agent that runs on each node in a cluster.
Handles the control plane’s instructions to run containers, performing:
- watches API server for new tasks
- Delegates these tasks to the container runtime
- Reports the status of tasks back to the API Server
If the Kubelet cant run a task it will report back to API
