Standardized Glossary
This glossary is intended to be a comprehensive, standardized list of Kubernetes terminology. It includes technical terms that are specific to K8s, as well as more general terms that provide useful context.
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Click on the [+] indicators below to get a longer explanation for any particular term.
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Cloud Controller Manager
Cloud Controller Manager is an alpha feature in 1.8. In upcoming releases it will be the preferred way to integrate Kubernetes with any cloud.
[+]Kubernetes v1.6 contains a new binary called cloud-controller-manager. cloud-controller-manager is a daemon that embeds cloud-specific control loops. These cloud-specific control loops were originally in the kube-controller-manager. Since cloud providers develop and release at a different pace compared to the Kubernetes project, abstracting the provider-specific code to the cloud-controller-manager binary allows cloud vendors to evolve independently from the core Kubernetes code.
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ConfigMap
An API object used to store non-confidential data in key-value pairs. Can be consumed as environment variables, command-line arguments, or config files in a volumeA directory containing data, accessible to the containers in a pod. .
[+]Allows you to decouple environment-specific configuration from your container imagesThe lifecycle hooks expose events in the container management lifecycle and let the user run code when the events occur. , so that your applications are easily portable. When storing confidential data use a Secret.
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DaemonSet
Ensures a copy of a PodA high-level summary of what phase the Pod is in within its lifecyle. is running across a set of nodes in a clusterA set of machines, called nodes, that run containerized applications managed by Kubernetes. .
[+]Used to deploy system daemons such as log collectors and monitoring agents that typically must run on every NodeA node is a worker machine in Kubernetes. .
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Deployment
An API object that manages a replicated application.
[+]Each replica is represented by a Pod LifecycleA high-level summary of what phase the Pod is in within its lifecyle. , and the Pods are distributed among the nodes of a cluster.
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Dynamic Volume Provisioning
Allows users to request automatic creation of storage VolumesA directory containing data, accessible to the containers in a pod. .
[+]Dynamic provisioning eliminates the need for cluster administrators to pre-provision storage. Instead, it automatically provisions storage by user request. Dynamic volume provisioning is based on an API object, StorageClassA StorageClass provides a way for administrators to describe different available storage types. , referring to a Volume PluginA Volume Plugin enables integration of storage within a Pod. that provisions a VolumeA directory containing data, accessible to the containers in a pod. and the set of parameters to pass to the Volume Plugin.
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Job
A finite or batch task that runs to completion.
[+]Creates one or more Pod LifecycleA high-level summary of what phase the Pod is in within its lifecyle. objects and ensures that a specified number of them successfully terminate. As Pods successfully complete, the Job tracks the successful completions.
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Kubelet
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.
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Persistent Volume
An API object that represents a piece of storage in the cluster. Available as a general, pluggable resource that persists beyond the lifecycle of any individual PodA high-level summary of what phase the Pod is in within its lifecyle. .
[+]PersistentVolumes (PVs) provide an API that abstracts details of how storage is provided from how it is consumed. PVs are used directly in scenarios where storage can be created ahead of time (static provisioning). For scenarios that require on-demand storage (dynamic provisioning), PersistentVolumeClaims (PVCs) are used instead.
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Persistent Volume Claim
Claims storage resources defined in a PersistentVolume so that it can be mounted as a volume in a container.
[+]Specifies the amount of storage, how the storage will be accessed (read-only, read-write and/or exclusive) and how it is reclaimed (retained, recycled or deleted). Details of the storage itself are in the PersistentVolume specification.
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Pod
The smallest and simplest Kubernetes object. A Pod represents a set of running containersThe lifecycle hooks expose events in the container management lifecycle and let the user run code when the events occur. on your cluster.
[+]A Pod is typically set up to run a single primary container. It can also run optional sidecar containers that add supplementary features like logging. Pods are commonly managed by a DeploymentAn API object that manages a replicated application. .
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Pod Security Policy
Enables fine-grained authorization of Pod LifecycleA high-level summary of what phase the Pod is in within its lifecyle. creation and updates.
[+]A cluster-level resource that controls security sensitive aspects of the Pod specification. The
PodSecurityPolicyobjects define a set of conditions that a Pod must run with in order to be accepted into the system, as well as defaults for the related fields. Pod Security Policy control is implemented as an optional admission controller. -
Quantity
A whole-number representation of small or large numbers using SI suffixes.
[+]Quantities are representations of small or large numbers using a compact, whole-number notation with SI suffixes. Fractional numbers are represented using milli units, while large numbers can be represented using kilo, mega, or giga units.
For instance, the number
1.5is represented as1500m, while the number1000can be represented as1k, and1000000as1M. You can also specify binary-notation suffixes; the number 2048 can be written as2Ki.The accepted decimal (power-of-10) units are
m(milli),k(kilo, intentionally lowercase),M(mega),G(giga),T(terra),P(peta),E(exa).The accepted binary (power-of-2) units are
Ki(kibi),Mi(mebi),Gi(gibi),Ti(tebi),Pi(pebi),Ei(exbi). -
ReplicaSet
ReplicaSet is the next-generation Replication Controller.
[+]ReplicaSet, like ReplicationController, ensures that a specified number of pods replicas are running at one time. ReplicaSet supports the new set-based selector requirements as described in the labels user guide, whereas a Replication Controller only supports equality-based selector requirements.
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Replication Controller
Kubernetes service that ensures a specific number of instances of a pod are always running.
[+]Will automatically add or remove running instances of a pod, based on a set value for that pod. Allows the pod to return to the defined number of instances if pods are deleted or if too many are started by mistake.
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Secret
Stores sensitive information, such as passwords, OAuth tokens, and ssh keys.
[+]Allows for more control over how sensitive information is used and reduces the risk of accidental exposure, including encryption at rest. A PodA high-level summary of what phase the Pod is in within its lifecyle. references the secret as a file in a volume mount or by the kubelet pulling images for a pod. Secrets are great for confidential data and ConfigMaps for non-confidential data.
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Service
An API object that describes how to access applications, such as a set of PodsA high-level summary of what phase the Pod is in within its lifecyle. , and can describe ports and load-balancers.
[+]The access point can be internal or external to the cluster.
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Service Account
Provides an identity for processes that run in a PodA high-level summary of what phase the Pod is in within its lifecyle. .
[+]When processes inside Pods access the cluster, they are authenticated by the API server as a particular service account, for example,
default. When you create a Pod, if you do not specify a service account, it is automatically assigned the default service account in the same namespace NamespaceAn abstraction used by Kubernetes to support multiple virtual clusters on the same physical cluster. . -
StatefulSet
Manages the deployment and scaling of a set of PodsA high-level summary of what phase the Pod is in within its lifecyle. , and provides guarantees about the ordering and uniqueness of these Pods.
[+]Like a DeploymentAn API object that manages a replicated application. , a StatefulSet manages Pods that are based on an identical container spec. Unlike a Deployment, a StatefulSet maintains a sticky identity for each of their Pods. These pods are created from the same spec, but are not interchangeable: each has a persistent identifier that it maintains across any rescheduling.
A StatefulSet operates under the same pattern as any other Controller. You define your desired state in a StatefulSet object, and the StatefulSet controller makes any necessary updates to get there from the current state.
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Storage Class
A StorageClass provides a way for administrators to describe different available storage types.
[+]StorageClasses can map to quality-of-service levels, backup policies, or to arbitrary policies determined by cluster administrators. Each StorageClass contains the fields
provisioner,parameters, andreclaimPolicy, which are used when a Persistent VolumeAn API object that represents a piece of storage in the cluster. Available as a general, pluggable resource that persists beyond the lifecycle of any individual Pod. belonging to the class needs to be dynamically provisioned. Users can request a particular class using the name of a StorageClass object. -
Taint
A key-value pair and an effect to prevent the scheduling of pods on nodes or node groups.
[+]Taints and TolerationsA key-value pair and an effect to enable the scheduling of pods on nodes or node groups that have a matching {% glossary_tooltip term_id=“taint” %}. work together to ensure that pods are not scheduled onto inappropriate nodes. One or more taints are applied to a nodeA node is a worker machine in Kubernetes. ; this marks that the nodeA node is a worker machine in Kubernetes. should not accept any pods that do not tolerate the taints.
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Toleration
A key-value pair and an effect to enable the scheduling of pods on nodes or node groups that have a matching taintsA key-value pair and an effect to prevent the scheduling of pods on nodes or node groups. .
[+]Tolerations and TaintsA key-value pair and an effect to prevent the scheduling of pods on nodes or node groups. work together to ensure that pods are not scheduled onto inappropriate nodes. One or more tolerations are applied to a podA high-level summary of what phase the Pod is in within its lifecyle. ; this marks that the podA high-level summary of what phase the Pod is in within its lifecyle. is allowed (but not required) to be scheduled on nodes or node groups with matching taintsA key-value pair and an effect to prevent the scheduling of pods on nodes or node groups. .
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Volume
A directory containing data, accessible to the containers in a podA high-level summary of what phase the Pod is in within its lifecyle. .
[+]A Kubernetes volume lives as long as the podA high-level summary of what phase the Pod is in within its lifecyle. that encloses it. Consequently, a volume outlives any containersThe lifecycle hooks expose events in the container management lifecycle and let the user run code when the events occur. that run within the podA high-level summary of what phase the Pod is in within its lifecyle. , and data is preserved across containerThe lifecycle hooks expose events in the container management lifecycle and let the user run code when the events occur. restarts.
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Volume Plugin
A Volume Plugin enables integration of storage within a PodA high-level summary of what phase the Pod is in within its lifecyle. .
[+]A Volume Plugin lets you attach and mount storage volumes for use by a PodA high-level summary of what phase the Pod is in within its lifecyle. . Volume plugins can be in tree or out of tree. In tree plugins are part of the Kubernetes code repository and follow its release cycle. Out of tree plugins are developed independently.
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kube-proxy
[+]kube-proxyis a network proxy that runs on each node in the cluster.kube-proxyis responsible for request forwarding.kube-proxyallows TCP and UDP stream forwarding or round robin TCP and UDP forwarding across a set of backend functions.
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