Kubernetes Overview

Master Server Role

– One server or a pod functions as the master server
Master server role has these jobs/components:

    • Gateway and control panel for the cluster via API
    • Perform health checks on other nodes
    • Schedule workloads and manage scaling
    • Link all components and adjust networking
    • Authenticate clients and nodes

Declaration plan (JSON or YAML format)

    • Start user-defined application or service
    • Master server executes plan by examining current state of system
    • etcd is a protocol to distribute configuration values within the cluster. Its methods allow applications to select, update, delete shits programmatically.
    • Kubernetes uses etcd to allow nodes to reconfigure themselves.

kube-apiserver provides RESTful interface for kubectl (clients)
kube-scheduler assigns workloads
kube-controller-manager regulates the cluster
cloud-controller-manager connects to various cloud environments to provide a uniform dashboard

Node Server Components

Container Runtime can be serviced by Docker, rkt, or runc
kubelet authenticates to the cluster and receive manifest (work) and controls Container Runtime. Report state of node to Master server.
kube-proxy: run on each node to ensure networking is streamlined

Objects

Pod is a group of nodes that perform similar functions, share life cycle. These nodes share environment, volumes, and supernets
Replication Controller defines pod template to scale replicas horizontally. It can perform updates on sets of pods without affecting availability.
Replication Sets are the run-time copies of Replication Controller design. It’s meant to be selected by Deployments (workloads)
Deployments are high-level objects accessible to the user. Similar to Replication Controller in functionality while differing in the easy of roll-back features.
Stateful Sets is a specialized pod controller, often associated with persistent databases. It acts as a pod controller to guarantee stability in networking and storage. It does this by tracking IDs for each pod
Daemon Sets is a type of pod controller, often associated with node services such as collecting metrics, gathering logs. These can bypass pod restrictions to ensure essential services are available to nodes.
Jobs are one-off tasks. Kubernetes also has Cron Jobs that function just like the sub-system Cron.
Service is a group of pods that performs the same functionality. There are Internal (SQL) and External Services (Apache/Nginx)
NodePort maps the node’s external IP with the cluster IP service
LoadBalancer creates external balancer route to Services
Volumes are Kubernetes construct that allow all containers in a pod to share. These exist until the Pod is terminated
Persistent Volumes are made to survive the pod’s life cycle as defined by their reclaimation policy
Labels are tags on Controller-based objects and Services. Each unit can have multiple labels, but it can only have 1 key entry. Semantics such as DEV, QA, STAGE, PROD, VERSION-X, etc are good examples of usage
Annotations are aggregates of Labels. They’re useful for metadata and expanded descriptions

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