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Nbc 2016 Volume 1 Pdf Download

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On-disk files in a container are ephemeral, which presents some problems fornon-trivial applications when running in containers. One problem occurs whena container crashes or is stopped. Container state is not saved so all of thefiles that were created or modified during the lifetime of the container are lost.During a crash, kubelet restarts the container with a clean state.Another problem occurs when multiple containers are running in a Pod andneed to share files. It can be challenging to setupand access a shared filesystem across all of the containers.The Kubernetes volume abstractionsolves both of these problems.Familiarity with Pods is suggested.



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Kubernetes supports many types of volumes. A Podcan use any number of volume types simultaneously.Ephemeral volume types have a lifetime of a pod,but persistent volumes exist beyondthe lifetime of a pod. When a pod ceases to exist, Kubernetes destroys ephemeral volumes;however, Kubernetes does not destroy persistent volumes.For any kind of volume in a given pod, data is preserved across container restarts.


At its core, a volume is a directory, possibly with some data in it, whichis accessible to the containers in a pod. How that directory comes to be, themedium that backs it, and the contents of it are determined by the particularvolume type used.


To use a volume, specify the volumes to provide for the Pod in .spec.volumesand declare where to mount those volumes into containers in .spec.containers[*].volumeMounts.A process in a container sees a filesystem view composed from the initial contents ofthe container image, plus volumes(if defined) mounted inside the container.The process sees a root filesystem that initially matches the contents of the containerimage.Any writes to within that filesystem hierarchy, if allowed, affect what that process viewswhen it performs a subsequent filesystem access.Volumes mount at the specified paths withinthe image.For each container defined within a Pod, you must independently specify whereto mount each volume that the container uses.


A cephfs volume allows an existing CephFS volume to bemounted into your Pod. Unlike emptyDir, which is erased when a pod isremoved, the contents of a cephfs volume are preserved and the volume is merelyunmounted. This means that a cephfs volume can be pre-populated with data, andthat data can be shared between pods. The cephfs volume can be mounted by multiplewriters simultaneously.


A ConfigMapprovides a way to inject configuration data into pods.The data stored in a ConfigMap can be referenced in a volume of typeconfigMap and then consumed by containerized applications running in a pod.






When referencing a ConfigMap, you provide the name of the ConfigMap in thevolume. You can customize the path to use for a specificentry in the ConfigMap. The following configuration shows how to mountthe log-config ConfigMap onto a Pod called configmap-pod:


The log-config ConfigMap is mounted as a volume, and all contents stored inits log_level entry are mounted into the Pod at path /etc/config/log_level.Note that this path is derived from the volume's mountPath and the pathkeyed with log_level.


For a Pod that defines an emptyDir volume, the volume is created when the Pod is assigned to a node.As the name says, the emptyDir volume is initially empty. All containers in the Pod can read and write the samefiles in the emptyDir volume, though that volume can be mounted at the sameor different paths in each container. When a Pod is removed from a node forany reason, the data in the emptyDir is deleted permanently.


The emptyDir.medium field controls where emptyDir volumes are stored. Bydefault emptyDir volumes are stored on whatever medium that backs the nodesuch as disk, SSD, or network storage, depending on your environment. If you setthe emptyDir.medium field to "Memory", Kubernetes mounts a tmpfs (RAM-backedfilesystem) for you instead. While tmpfs is very fast be aware that, unlikedisks, files you write count against the memory limit of the container that wrote them.


A size limit can be specified for the default medium, which limits the capacityof the emptyDir volume. The storage is allocated from node ephemeralstorage.If that is filled up from another source (for example, log files or imageoverlays), the emptyDir may run out of capacity before this limit.


An fc volume type allows an existing fibre channel block storage volumeto mount in a Pod. You can specify single or multiple target world wide names (WWNs)using the parameter targetWWNs in your Volume configuration. If multiple WWNs are specified,targetWWNs expect that those WWNs are from multi-path connections.


If you are restricting access to specific directories on the node usingadmission-time validation, that restriction is only effective when youadditionally require that any mounts of that hostPath volume areread only. If you allow a read-write mount of any host path by anuntrusted Pod, the containers in that Pod may be able to subvert theread-write host mount.


Some files or directories created on the underlying hosts might only beaccessible by root. You then either need to run your process as root in aprivileged containeror modify the file permissions on the host to be able to read from(or write to) a hostPath volume.


---# This manifest mounts /data/foo on the host as /foo inside the# single container that runs within the hostpath-example-linux Pod.## The mount into the container is read-only.apiVersion: v1kind: Podmetadata: name: hostpath-example-linuxspec: os:  name: linux  nodeSelector: kubernetes.io/os: linux containers: - name: example-container image: registry.k8s.io/test-webserver volumeMounts: - mountPath: /foo name: example-volume readOnly: true volumes: - name: example-volume # mount /data/foo, but only if that directory already exists hostPath: path: /data/foo # directory location on host type: Directory # this field is optional---# This manifest mounts C:\Data\foo on the host as C:\foo, inside the# single container that runs within the hostpath-example-windows Pod.## The mount into the container is read-only.apiVersion: v1kind: Podmetadata: name: hostpath-example-windowsspec: os:  name: windows  nodeSelector: kubernetes.io/os: windows containers: - name: example-container image: microsoft/windowsservercore:1709 volumeMounts: - name: example-volume mountPath: "C:\\foo" readOnly: true volumes: # mount C:\Data\foo from the host, but only if that directory already exists - name: example-volume hostPath: path: "C:\\Data\\foo" # directory location on host type: Directory # this field is optionalhostPath FileOrCreate configuration exampleThe following manifest defines a Pod that mounts /var/local/aaainside the single container in the Pod. If the node does notalready have a path /var/local/aaa, the kubelet createsit as a directory and then mounts it into the Pod.


An iscsi volume allows an existing iSCSI (SCSI over IP) volume to be mountedinto your Pod. Unlike emptyDir, which is erased when a Pod is removed, thecontents of an iscsi volume are preserved and the volume is merelyunmounted. This means that an iscsi volume can be pre-populated with data, andthat data can be shared between pods.


A feature of iSCSI is that it can be mounted as read-only by multiple consumerssimultaneously. This means that you can pre-populate a volume with your datasetand then serve it in parallel from as many Pods as you need. Unfortunately,iSCSI volumes can only be mounted by a single consumer in read-write mode.Simultaneous writers are not allowed.


Compared to hostPath volumes, local volumes are used in a durable andportable manner without manually scheduling pods to nodes. The system is awareof the volume's node constraints by looking at the node affinity on the PersistentVolume.


However, local volumes are subject to the availability of the underlyingnode and are not suitable for all applications. If a node becomes unhealthy,then the local volume becomes inaccessible by the pod. The pod using this volumeis unable to run. Applications using local volumes must be able to tolerate thisreduced availability, as well as potential data loss, depending on thedurability characteristics of the underlying disk.


When using local volumes, it is recommended to create a StorageClass withvolumeBindingMode set to WaitForFirstConsumer. For more details, see thelocal StorageClass example.Delaying volume binding ensures that the PersistentVolumeClaim binding decisionwill also be evaluated with any other node constraints the Pod may have,such as node resource requirements, node selectors, Pod affinity, and Pod anti-affinity.


An external static provisioner can be run separately for improved management ofthe local volume lifecycle. Note that this provisioner does not support dynamicprovisioning yet. For an example on how to run an external local provisioner,see the local volume provisioner userguide.


An nfs volume allows an existing NFS (Network File System) share to bemounted into a Pod. Unlike emptyDir, which is erased when a Pod isremoved, the contents of an nfs volume are preserved and the volume is merelyunmounted. This means that an NFS volume can be pre-populated with data, andthat data can be shared between pods. NFS can be mounted by multiplewriters simultaneously.


Also note that you can't specify NFS mount options in a Pod spec. You can either set mount options server-side oruse /etc/nfsmount.conf.You can also mount NFS volumes via PersistentVolumes which do allow you to set mount options.


A persistentVolumeClaim volume is used to mount aPersistentVolume into a Pod. PersistentVolumeClaimsare a way for users to "claim" durable storage (such as an iSCSI volume)without knowing the details of the particular cloud environment.


An rbd volume allows aRados Block Device (RBD) volume to mountinto your Pod. Unlike emptyDir, which is erased when a pod is removed, thecontents of an rbd volume are preserved and the volume is unmounted. Thismeans that a RBD volume can be pre-populated with data, and that data can beshared between pods.

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Nbc 2016 Volume 1 Pdf Download Nancie Fazzari <fazzarinancie@gmail.com> - 2024-01-18 07:04 -0800

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