Basic Concepts Flashcards
What are the elements of the control plane?
- etcd (KV store)
- API server
- scheduler
- controller manager
- cloud controller manager
etcd
- distributed KV store for cluster state
- how many resources are running, status of resources, etc
- stores and replicates all cluster states
- “et-see-dee”
- distributed etc directory
API server
used by pods and users to communicate with the control plane
accepts REST commands to interact with cluster resources
Controller Manager
- control loop that makes sure the etcd state matches the node state
- for example, if a workflow requires 3 replicas and 1 replica is down, the controller manager sends a command to restore it
Worker Nodes
- the compute on which containers are executed
- can be a physical or virtual machine depending on the cluster
- managed by the control plane and contain the necessary services to run pods
- if nodes are unavailable, kubernetes cannot run workloads
What is kubernetes?
- An orchestration platform for running containers
- Runs workloads by placing containers into pods to run on nodes
- Schedules pods on nodes on a best-effort basis
What are the elements of a node?
All nodes need to be bootstrapped with
- kubeproxy
- kubelet
- container runtime (e.g. docker)
Cardoning
Stop new workflows from being scheduled
Draining
Start moving workflows off a given node
What is a kubernetes cluster?
- Physical isolation of hardware (set of connected nodes)
- Combination of control plane and worker nodes
What is the control plane?
A controller that runs in a loop trying to ensure that the cluster is in a desired state
Namespaces
- Provide logical isolation of workloads
- Helpful for provisioning cluster resources
- Kubernetes resources must live within a namespace unless they are cluster-scoped
What is tainting?
Allows for customizable scheduling of nodes
When you taint a node, you need a pod to tolerate that taint
Taints and tolerations are how pods are scheduled on nodes
kubeproxy
- responsible for communication between the control plane and the node itself
- network proxy that runs on each node in a cluster o maintain network rules and enable network communication
kubelet
- takes instructions from control plane and executes them on the node
- agent that gets the pod config from the api server and ensures the pods and container state have the desired config
kubectl
- kube CTL
- application to interact with the kubernetes cluster
Pods
- Smallest deployable units of compute that you can deploy and manage in Kubernetes
- Run the workflow
- Group of containers with shared storage and network resources and a specification for how to run the containers
When is a pod considered up?
When all the containers are in a running state
What are initcontainers?
- Allow preconfigurations such as bootstrap and auth credentials
What are affinity and non-affinity?
How pods are scheduled with respect to other pods
What is a readiness probe?
Used to determine whether a pod is ready to accept traffic
What is a liveness probe?
Used to determine whether or not a pod is healthy
kube scheduler
- background process that watches for new kubernetes pods with no assigned nodes and assigns them to a worker node for execution
controller
manage kubernetes jobs
etc (linux)
- “et-see”
- store config files and dirs for the OS applications
container runtime engine
- software responsible for managing containers (e.g. Docker)
