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Components

Main Objects

Concept Description Diagram
node
  • A machine in the cluster
  • Can be physical or virtual
pod
  • Group of containers running on the same host
  • Configured to share a network stack and other resources such as volumes
deployments
  • Requirements you give to Kubernetes regarding your applications (your Pods)
  • Allows scaling, rolling updates, rollbacks
  • Multiple deployments can be used together to implement a canary deployment
  • Delegates pods management to replica sets
  • A Kubernetes process (the scheduler) continually checks the state of all the Deployments
service
  • Abstract way to expose an app as a network service
  • Causes a proxy to be configured to forward requests to a set of pods
  • Services are stable network endpoint to connect to one or multiple containers
    • Single, unchanging IP address or DNS name which will be automatically routed to any matching Pod
    • Services allow to talk to pods from within the cluster
  • Service DNS names always follow this pattern: SERVICE.NAMESPACE.svc.cluster.local
ingress
  • Ingress objects are rules that define the routes to our Services
  • They expose Services to the internet

Supporting Objects

Concept Description
namespace
  • Abstraction used to support multiple virtual clusters on the same physical cluster
ReplicaSet
  • Low-level construct
  • Makes sure that a given number of identical pods are running (allows scaling)
  • Rarely used directly
DaemonSet
  • Ensures a copy of a Pod is running across a set of nodes
StatefulSet
  • Provides guarantees about the ordering and uniqueness of Pods
  • Maintains a sticky identity for each Pod (across rescheduling)
Secret
  • Stores sensitive information
ConfigMap
  • Object used to store non-confidential data in key-value pairs
  • Can be consumed as:
    • environment variables
    • command line arguments
    • config files in a volume

Additional Components

Concept Description
etcd
  • Consistent and highly-available key value store used as Kubernetes' backing store for all cluster data
  • It stores the cluster state including items like service tokens, secrets and service configurations
kubelet
  • Primary "node agent" that runs on each node
  • It works in terms of a PodSpec, a YAML or JSON object that describes a pod
  • The kubelet takes a set of PodSpecs provided and ensures that the containers described in those PodSpecs are running and healthy

Standard pods

Name Description
etcd etcd server
kube-apiserver API server
kube-controller-manager
kube-scheduler
other master components
kube-dns additional component (not mandatory)
kube-proxy the (per-node) component managing port mappings and such
weave the (per-node) component managing the network overlay
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