Kubernetes Concepts
External
Internal
Overview
Kubernetes is an container orchestration platform, offering the ability of orchestrate Docker containers across multiple hosts. It manages containers in a clustered environment. It orchestrates containers at scale, defines application topologies, handles parts of the container networking, manages container state and schedules containers across hosts.
Master
Node
Pod
Storage
Persistent Volume
Represented by a PersistentVolume object. It is associated with a project.
An administrator provision persistent volumes from sources such as:
- NFS
- GCE Persistent Disks
- ESB Volumes
- GlusterFS
- OpenStack Cinder
- Ceph RBD
- iSCSI
- Fiber Channel
Storage resources are requested by laying a claim to the resource (PersistentVolumeClaim). A persistent volume claim is a request for a resource with a specific attributes. When a request is made, a process matches it to an available volume and binds them together. The runtime finds the volume bound to the claim and mounts it into the pod.
Persistent volumes can be recycled after use. The reclamation policy is based on the "persistentVolumeReclaimPolicy" declared in the PersistentVolume object definition. The policy can be "Retain" or "Recycle".
etcd
A distributed key/value datastore for state within the environment.
Scheduler
Namespace
A namespace provides scope for:
- named resources to avoid naming collisions
- delegating management authority to trusted users
- the ability to limit community resource consumption
Policies
Policies are rules that specify which users can and cannot specify actions on objects (pods, services, etc.).
Service
Service Definition File
API
Label
Selector
Replica
A replica is a set of pods sharing the same definition.