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K8s Glossary > Glossary > Flashcards

Glossary Flashcards

1
Q

Add-ons

A

Resources that extend the functionality of Kubernetes.

Installing addons explains more about using add-ons with your cluster, and lists some popular add-ons.

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2
Q

Admission Controller

A

A piece of code that intercepts requests to the Kubernetes API server prior to persistence of the object.

Admission controllers are configurable for the Kubernetes API server and may be “validating”, “mutating”, or both. Any admission controller may reject the request. Mutating controllers may modify the objects they admit; validating controllers may not.

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3
Q

Aggregation Layer

A

The aggregation layer lets you install additional Kubernetes-style APIs in your cluster.

When you’ve configured the Kubernetes API Server to support additional APIs, you can add APIService objects to “claim” a URL path in the Kubernetes API.

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4
Q

Annotation

A

A key-value pair that is used to attach arbitrary non-identifying metadata to objects.

The metadata in an annotation can be small or large, structured or unstructured, and can include characters not permitted by labels. Clients such as tools and libraries can retrieve this metadata.

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5
Q

API Group

A

A set of related paths in Kubernetes API.

You can enable or disable each API group by changing the configuration of your API server. You can also disable or enable paths to specific resources. API group makes it easier to extend the Kubernetes API. The API group is specified in a REST path and in the apiVersion field of a serialized object.

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6
Q

API server

A

Also known as:kube-apiserver

The API server is a component of the Kubernetes control plane that exposes the Kubernetes API. The API server is the front end for the Kubernetes control plane.

The main implementation of a Kubernetes API server is kube-apiserver. kube-apiserver is designed to scale horizontally—that is, it scales by deploying more instances. You can run several instances of kube-apiserver and balance traffic between those instances.

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7
Q

App Container

A

Application containers (or app containers) are the containers in a pod that are started after any init containers have completed.

An init container lets you separate initialization details that are important for the overall workload, and that don’t need to keep running once the application container has started. If a pod doesn’t have any init containers configured, all the containers in that pod are app containers.

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8
Q

Application Architect

A

A person responsible for the high-level design of an application.

An architect ensures that an app’s implementation allows it to interact with its surrounding components in a scalable, maintainable way. Surrounding components include databases, logging infrastructure, and other microservices

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9
Q

Application Developer

A

A person who writes an application that runs in a Kubernetes cluster.

An application developer focuses on one part of an application. The scale of their focus may vary significantly in size.

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10
Q

Applications

A

The layer where various containerized applications run.

The layer where various containerized applications run.

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11
Q

Approver

A

A person who can review and approve Kubernetes code contributions.

While code review is focused on code quality and correctness, approval is focused on the holistic acceptance of a contribution. Holistic acceptance includes backwards/forwards compatibility, adhering to API and flag conventions, subtle performance and correctness issues, interactions with other parts of the system, and others. Approver status is scoped to a part of the codebase. Approvers were previously referred to as maintainers.

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12
Q

Certificate

A

A cryptographically secure file used to validate access to the Kubernetes cluster.

Certificates enable applications within a Kubernetes cluster to access the Kubernetes API securely. Certificates validate that clients are allowed to access the API.

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13
Q

cgroup (control group)

A

A group of Linux processes with optional resource isolation, accounting and limits.

cgroup is a Linux kernel feature that limits, accounts for, and isolates the resource usage (CPU, memory, disk I/O, network) for a collection of processes.

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14
Q

CIDR

A

CIDR (Classless Inter-Domain Routing) is a notation for describing blocks of IP addresses and is used heavily in various networking configurations.

In the context of Kubernetes, each Node is assigned a range of IP addresses through the start address and a subnet mask using CIDR. This allows Nodes to assign each Pod a unique IP address. Although originally a concept for IPv4, CIDR has also been expanded to include IPv6

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15
Q

What is a node

A

A worker machine that run containerized applications.

Every cluster has at least one node.

Worker nodes host the pods

The control plane manages the worker nodes and the Pods in the cluster.

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16
Q

Waht is kube-apiserver

A

The Kubernetes API server validates and configures data for the api objects which include pods, services, replicationcontrollers, and others. The API Server services REST operations and provides the frontend to the cluster’s shared state through which all other components interact.

17
Q

What is etcd?

A

Consistent and highly-available key value store used as Kubernetes’ backing store for all cluster data.

If your Kubernetes cluster uses etcd as its backing store, make sure you have a back up plan for those data.

18
Q

What is kube-scheduler?

A

Control plane component that watches for newly created Pods with no assigned node, and selects a node for them to run on.

19
Q

Waht is kube-controller-manager

A

Control Plane component that runs controller processes.

Logically, each controller is a separate process, but to reduce complexity, they are all compiled into a single binary and run in a single process.

Some types of these controllers are:

Node controller: Responsible for noticing and responding when nodes go down.

Job controller: Watches for Job objects that represent one-off tasks, then creates Pods to run those tasks to completion.

Endpoints controller: Populates the Endpoints object (that is, joins Services & Pods).

Service Account & Token controllers: Create default accounts and API access tokens for new namespaces.

20
Q

cloud-controller-manager

A

A Kubernetes control plane component that embeds cloud-specific control logic. The cloud controller manager lets you link your cluster into your cloud provider’s API, and separates out the components that interact with that cloud platform from components that only interact with your cluster.

The cloud-controller-manager only runs controllers that are specific to your cloud provider. If you are running Kubernetes on your own premises, or in a learning environment inside your own PC, the cluster does not have a cloud controller manager.

21
Q

Node Components: What is a kubelet?

A

An agent that runs on each node in the cluster. It makes sure that containers are running in a Pod.

The kubelet takes a set of PodSpecs that are provided through various mechanisms and ensures that the containers described in those PodSpecs are running and healthy. The kubelet doesn’t manage containers which were not created by Kubernetes.

22
Q

Node Components: What is a kube-proxy?

A

kube-proxy is a network proxy that runs on each node in your cluster, implementing part of the Kubernetes Service concept.

kube-proxy maintains network rules on nodes. These network rules allow network communication to your Pods from network sessions inside or outside of your cluster.

kube-proxy uses the operating system packet filtering layer if there is one and it’s available. Otherwise, kube-proxy forwards the traffic itself.

23
Q

Node Components: what is Container runtime

A

The container runtime is the software that is responsible for running containers.

Kubernetes supports several container runtimes: Docker, containerd, CRI-O, and any implementation of the Kubernetes CRI (Container Runtime Interface).

24
Q

Addons: DNS

A

While the other addons are not strictly required, all Kubernetes clusters should have cluster DNS, as many examples rely on it.

Cluster DNS is a DNS server, in addition to the other DNS server(s) in your environment, which serves DNS records for Kubernetes services.

Containers started by Kubernetes automatically include this DNS server in their DNS searches.

25
Q

Addons: Web UI - Dashboard

A

Dashboard is a general purpose, web-based UI for Kubernetes clusters. It allows users to manage and troubleshoot applications running in the cluster, as well as the cluster itself.

26
Q

Addons: Container Resource Monitoring

A

Container Resource Monitoring records generic time-series metrics about containers in a central database, and provides a UI for browsing that data.

27
Q

Addons: Cluster-level logging

A

A cluster-level logging mechanism is responsible for saving container logs to a central log store with search/browsing interface

28
Q
A

K8s Glossary (1 decks)

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