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a Linux bastion host port forwarding on 3Engines Cloud </span> </a> </li> <li class=md-nav__item> <a href=../windows/How-to-connect-to-a-virtual-machine-via-SSH-from-Windows-10-Command-Prompt-on-3Engines-Cloud.html.html class=md-nav__link> <span class=md-ellipsis> How to connect to a virtual machine via SSH from Windows 10 Command Prompt on 3Engines Cloud </span> </a> </li> <li class=md-nav__item> <a href=../windows/How-To-Create-SSH-Key-Pair-In-Windows-On-3Engines-Cloud.html.html class=md-nav__link> <span class=md-ellipsis> How to Create SSH Key Pair in Windows 10 On 3Engines Cloud </span> </a> </li> <li class=md-nav__item> <a href=../windows/Can-I-change-my-password-through-RDP-on-3Engines-Cloud.html.html class=md-nav__link> <span class=md-ellipsis> Can I change my password through RDP on 3Engines Cloud? </span> </a> </li> <li class=md-nav__item> <a href=../windows/How-To-Create-SSH-Key-Pair-In-Windows-11-On-3Engines-Cloud.html.html class=md-nav__link> <span class=md-ellipsis> How to Create SSH Key Pair in Windows 11 On 3Engines Cloud </span> </a> </li> </ul> </nav> </li> </ul> </nav> </div> </div> </div> <div class="md-sidebar md-sidebar--secondary" data-md-component=sidebar data-md-type=toc> <div class=md-sidebar__scrollwrap> <div class=md-sidebar__inner> <nav class="md-nav md-nav--secondary" aria-label="On this page"> <label class=md-nav__title for=__toc> <span class="md-nav__icon md-icon"></span> On this page </label> <ul class=md-nav__list data-md-component=toc data-md-scrollfix> <li class=md-nav__item> <a href=#what-we-are-going-to-cover class=md-nav__link> <span class=md-ellipsis> What We Are Going To Cover🔗 </span> </a> </li> <li class=md-nav__item> <a href=#prerequisites class=md-nav__link> <span class=md-ellipsis> Prerequisites🔗 </span> </a> </li> <li class=md-nav__item> <a href=#step-1-create-cluster-using-docker-volume-size class=md-nav__link> <span class=md-ellipsis> Step 1 - Create Cluster Using –docker-volume-size🔗 </span> </a> </li> <li class=md-nav__item> <a href=#step-2-create-pod-manifest class=md-nav__link> <span class=md-ellipsis> Step 2 - Create Pod Manifest🔗 </span> </a> </li> <li class=md-nav__item> <a href=#step-3-create-a-pod-on-node-0-of-dockerspace class=md-nav__link> <span class=md-ellipsis> Step 3 - Create a Pod on Node 0 of dockerspace🔗 </span> </a> </li> <li class=md-nav__item> <a href=#step-4-executing-bash-commands-in-the-container class=md-nav__link> <span class=md-ellipsis> Step 4 - Executing bash Commands in the Container🔗 </span> </a> </li> <li class=md-nav__item> <a href=#step-5-saving-a-file-into-persistent-storage class=md-nav__link> <span class=md-ellipsis> Step 5 - Saving a File Into Persistent Storage🔗 </span> </a> </li> <li class=md-nav__item> <a href=#step-6-check-the-file-saved-in-previous-step class=md-nav__link> <span class=md-ellipsis> Step 6 - Check the File Saved in Previous Step🔗 </span> </a> </li> <li class=md-nav__item> <a href=#what-to-do-next class=md-nav__link> <span class=md-ellipsis> What To Do Next🔗 </span> </a> </li> </ul> </nav> </div> </div> </div> <div class=md-content data-md-component=content> <article class="md-content__inner md-typeset"> <h1 id=volume-based-vs-ephemeral-based-storage-for-kubernetes-clusters-on-3engines-cloud-openstack-magnum>Volume-based vs Ephemeral-based Storage for Kubernetes Clusters on 3Engines Cloud OpenStack Magnum<a href=#volume-based-vs-ephemeral-based-storage-for-kubernetes-clusters-on-brand-name-openstack-magnum title="Permalink to this headline">🔗</a><a class=headerlink href=#volume-based-vs-ephemeral-based-storage-for-kubernetes-clusters-on-3engines-cloud-openstack-magnum title="Permanent link">&para;</a></h1> <p>Containers in Kubernetes store files on-disk and if the container crashes, the data will be lost. A new container can replace the old one but the data will not survive. Another problem that appears is when containers running in a pod need to share files.</p> <p>That is why Kubernetes has another type of file storage, called <em>volumes</em>. They can be either <em>persistent</em> or <em>ephemeral</em>, as measured against the lifetime of a pod:</p> <blockquote> <ul> <li>Ephemeral volumes are deleted when the pod is deleted, while</li> <li>Persistent volumes continue to exist even if the pod it is attached to does not exist any more.</li> </ul> </blockquote> <p>The concept of volumes was first popularized by Docker, where it was a directory on disk, or within a container. In 3Engines Cloud OpenStack hosting, the default docker storage is configured to use ephemeral disk of the instance. This can be changed by specifying docker volume size during cluster creation, symbolically like this (see below for the full command to generate a new cluster using <strong>–docker-volume-size</strong>):</p> <div class=highlight><pre><span></span><code><span id=__span-0-1><a id=__codelineno-0-1 name=__codelineno-0-1 href=#__codelineno-0-1></a>openstack coe cluster create --docker-volume-size 50
</span></code></pre></div> <p>This means that a persistent volume of 50 GB will be created and attached to the pod. Using <strong>–docker-volume-size</strong> is a way to both reserve the space and declare that the storage will be persistent.</p> <h2 id=what-we-are-going-to-cover>What We Are Going To Cover<a href=#what-we-are-going-to-cover title="Permalink to this headline">🔗</a><a class=headerlink href=#what-we-are-going-to-cover title="Permanent link">&para;</a></h2> <blockquote> <ul> <li>How to create a cluster when <strong>–docker-volume-size</strong> is used</li> <li>How to create a pod manifest with <em>emptyDir</em> as volume</li> <li>How to create a pod with that manifest</li> <li>How to execute <em>bash</em> commands in the container</li> <li>How to save a file into persistent storage</li> <li>How to demonstrate that the attached volume is persistent</li> </ul> </blockquote> <h2 id=prerequisites>Prerequisites<a href=#prerequisites title="Permalink to this headline">🔗</a><a class=headerlink href=#prerequisites title="Permanent link">&para;</a></h2> <p>1 <strong>Hosting</strong></p> <p>You need a 3Engines Cloud hosting account with Horizon interface <a href=https://horizon.3Engines.com>https://horizon.3Engines.com</a>.</p> <p>2 <strong>Creating clusters with CLI</strong></p> <p>The article <a href=How-To-Use-Command-Line-Interface-for-Kubernetes-Clusters-On-3Engines-Cloud-OpenStack-Magnum.html.html>How To Use Command Line Interface for Kubernetes Clusters On 3Engines Cloud OpenStack Magnum</a> will introduce you to creation of clusters using a command line interface.</p> <p>3 <strong>Connect openstack client to the cloud</strong></p> <p>Prepare <strong>openstack</strong> and <strong>magnum</strong> clients by executing <em>Step 2 Connect OpenStack and Magnum Clients to Horizon Cloud</em> from article <a href=How-To-Install-OpenStack-and-Magnum-Clients-for-Command-Line-Interface-to-3Engines-Cloud-Horizon.html.html>How To Install OpenStack and Magnum Clients for Command Line Interface to 3Engines Cloud Horizon</a></p> <p>4 <strong>Check available quotas</strong></p> <p>Before creating additional cluster check the state of the resources with Horizon commands <strong>Computer</strong> =&gt; <strong>Overview</strong>.</p> <p>5 <strong>Private and public keys</strong></p> <p>An SSH key-pair created in OpenStack dashboard. To create it, follow this article <a href=../cloud/How-to-create-key-pair-in-OpenStack-Dashboard-on-3Engines-Cloud.html.html>How to create key pair in OpenStack Dashboard on 3Engines Cloud</a>. You will have created keypair called “sshkey” and you will be able to use it for this tutorial as well.</p> <p>6 <strong>Types of Volumes</strong></p> <p>Types of volumes are described in the <a href=https://kubernetes.io/docs/concepts/storage/volumes/ >official Kubernetes documentation</a>.</p> <h2 id=step-1-create-cluster-using-docker-volume-size>Step 1 - Create Cluster Using <strong>–docker-volume-size</strong><a href=#step-1-create-cluster-using-docker-volume-size title="Permalink to this headline">🔗</a><a class=headerlink href=#step-1-create-cluster-using-docker-volume-size title="Permanent link">&para;</a></h2> <p>You are going to create a new cluster called <em>dockerspace</em> that will use parameter <strong>–docker-volume-size</strong> using the following command:</p> <div class=highlight><pre><span></span><code><span id=__span-1-1><a id=__codelineno-1-1 name=__codelineno-1-1 href=#__codelineno-1-1></a>openstack coe cluster create dockerspace
</span><span id=__span-1-2><a id=__codelineno-1-2 name=__codelineno-1-2 href=#__codelineno-1-2></a> --cluster-template k8s-1.23.16-cilium-v1.0.3
</span><span id=__span-1-3><a id=__codelineno-1-3 name=__codelineno-1-3 href=#__codelineno-1-3></a> --keypair sshkey
</span><span id=__span-1-4><a id=__codelineno-1-4 name=__codelineno-1-4 href=#__codelineno-1-4></a> --master-count 1
</span><span id=__span-1-5><a id=__codelineno-1-5 name=__codelineno-1-5 href=#__codelineno-1-5></a> --node-count 2
</span><span id=__span-1-6><a id=__codelineno-1-6 name=__codelineno-1-6 href=#__codelineno-1-6></a> --docker-volume-size 50
</span><span id=__span-1-7><a id=__codelineno-1-7 name=__codelineno-1-7 href=#__codelineno-1-7></a> --master-flavor eo1.large
</span><span id=__span-1-8><a id=__codelineno-1-8 name=__codelineno-1-8 href=#__codelineno-1-8></a> --flavor eo2.large
</span></code></pre></div> <p>After a few minutes the new cluster <strong>dockerspace</strong> will be created.</p> <p>Click on <strong>Container Infra</strong> =&gt; <strong>Clusters</strong> to show the three clusters in the system: <em>authenabled</em>, <em>k8s-cluster</em> and <em>dockerspace</em>.</p> <p><a class=glightbox href=../_images/dockerspace_created.png data-type=image data-width=100% data-height=auto data-desc-position=bottom><img alt=dockerspace_created.png src=../_images/dockerspace_created.png></a></p> <p>Here are their instances (after clicking on <strong>Compute</strong> =&gt; <strong>Instances</strong>):</p> <p><a class=glightbox href=../_images/instances.png data-type=image data-width=100% data-height=auto data-desc-position=bottom><img alt=instances.png src=../_images/instances.png></a></p> <p>They will have at least two instances each, one for the master and one for the worker node. <em>dockerspace</em> has three instances as it has two worker nodes, created with flavor <em>eo2.large</em>.</p> <p>So far so good, nothing out of the ordinary. Click on <strong>Volumes</strong> =&gt; <strong>Volumes</strong> to show the list of volumes:</p> <p><a class=glightbox href=../_images/volumes.png data-type=image data-width=100% data-height=auto data-desc-position=bottom><img alt=volumes.png src=../_images/volumes.png></a></p> <p>If <strong>–docker-volume-size</strong> is not turned on, only instances with <em>etcd-volume</em> in their names would appear here, as is the case for clusters <em>authenabled</em> and <em>k8s-cluster</em>. If it is turned on, additional volumes would appear, one for each node. <em>dockerspace</em> will, therefore, have one instance for master and two instances for worker nodes.</p> <p>Note the column <strong>Attached</strong>. All nodes for <em>dockerspace</em> use <strong>/dev/vdb</strong> for storage, which is a fact that will be important later on.</p> <p>As specified during creation, <em>docker-volumes</em> have size of 50 GB each.</p> <p>In this step, you have created a new cluster with docker storage turned on and then you verified that the main difference lies in creation of volumes for the cluster.</p> <h2 id=step-2-create-pod-manifest>Step 2 - Create Pod Manifest<a href=#step-2-create-pod-manifest title="Permalink to this headline">🔗</a><a class=headerlink href=#step-2-create-pod-manifest title="Permanent link">&para;</a></h2> <p>To create a pod, you need to use a file in <em>yaml</em> format that defines the parameters of the pod. Use command</p> <div class=highlight><pre><span></span><code><span id=__span-2-1><a id=__codelineno-2-1 name=__codelineno-2-1 href=#__codelineno-2-1></a>nano redis.yaml
</span></code></pre></div> <p>to create file called <em>redis.yaml</em> and copy the following rows into it:</p> <div class=highlight><pre><span></span><code><span id=__span-3-1><a id=__codelineno-3-1 name=__codelineno-3-1 href=#__codelineno-3-1></a>apiVersion: v1
</span><span id=__span-3-2><a id=__codelineno-3-2 name=__codelineno-3-2 href=#__codelineno-3-2></a>kind: Pod
</span><span id=__span-3-3><a id=__codelineno-3-3 name=__codelineno-3-3 href=#__codelineno-3-3></a>metadata:
</span><span id=__span-3-4><a id=__codelineno-3-4 name=__codelineno-3-4 href=#__codelineno-3-4></a> name: redis
</span><span id=__span-3-5><a id=__codelineno-3-5 name=__codelineno-3-5 href=#__codelineno-3-5></a>spec:
</span><span id=__span-3-6><a id=__codelineno-3-6 name=__codelineno-3-6 href=#__codelineno-3-6></a> containers:
</span><span id=__span-3-7><a id=__codelineno-3-7 name=__codelineno-3-7 href=#__codelineno-3-7></a> - name: redis
</span><span id=__span-3-8><a id=__codelineno-3-8 name=__codelineno-3-8 href=#__codelineno-3-8></a> image: redis
</span><span id=__span-3-9><a id=__codelineno-3-9 name=__codelineno-3-9 href=#__codelineno-3-9></a> volumeMounts:
</span><span id=__span-3-10><a id=__codelineno-3-10 name=__codelineno-3-10 href=#__codelineno-3-10></a> - name: redis-storage
</span><span id=__span-3-11><a id=__codelineno-3-11 name=__codelineno-3-11 href=#__codelineno-3-11></a> mountPath: /data/redis
</span><span id=__span-3-12><a id=__codelineno-3-12 name=__codelineno-3-12 href=#__codelineno-3-12></a> volumes:
</span><span id=__span-3-13><a id=__codelineno-3-13 name=__codelineno-3-13 href=#__codelineno-3-13></a> - name: redis-storage
</span><span id=__span-3-14><a id=__codelineno-3-14 name=__codelineno-3-14 href=#__codelineno-3-14></a> emptyDir: {}
</span></code></pre></div> <p>This is how it will look like in the terminal:</p> <p><a class=glightbox href=../_images/nano_redis_yaml.png data-type=image data-width=100% data-height=auto data-desc-position=bottom><img alt=nano_redis_yaml.png src=../_images/nano_redis_yaml.png></a></p> <p>You are creating a <em>Pod</em>, its name will be <em>redis</em>, and it will occupy one container also called <em>redis</em>. The content of that container will be an image called <strong>redis</strong>.</p> <p>Redis is a well known database and its image is prepared in advance so can be pulled off directly from a repository. If you were implementing your own application, the best way would be to release it through Docker and pull from its repository.</p> <p>New volume is called <em>redis-storage</em> and its directory will be <em>/data/redis</em>. The name of the volume will again be <em>redis-storage</em> and it will be of type <em>emptyDir</em>.</p> <p>An <em>emptyDir</em> volume is initially empty and is first created when a Pod is assigned to a node. It will exist as long as that Pod is running there and if the Pod is removed, the related data in <em>emptyDir</em> will be deleted permanently. However, the data in an <em>emptyDir</em> volume is safe across container crashes.</p> <p>Besides <em>emptyDir</em>, about a dozen other volume types could have been used here: <em>awsElasticBlockStore</em>, <em>azureDisk</em>, <em>cinder</em> and so on.</p> <p>In this step, you have prepared pod manifest with which you will create the pod in the next step.</p> <h2 id=step-3-create-a-pod-on-node-0-of-dockerspace>Step 3 - Create a Pod on Node <strong>0</strong> of <em>dockerspace</em><a href=#step-3-create-a-pod-on-node-0-of-dockerspace title="Permalink to this headline">🔗</a><a class=headerlink href=#step-3-create-a-pod-on-node-0-of-dockerspace title="Permanent link">&para;</a></h2> <p>In this step you will create a new pod on node <strong>0</strong> of <em>dockerspace</em> cluster.</p> <p>First see what pods are available in the cluster:</p> <div class=highlight><pre><span></span><code><span id=__span-4-1><a id=__codelineno-4-1 name=__codelineno-4-1 href=#__codelineno-4-1></a>kubectl get pods
</span></code></pre></div> <p>This may produce error line such as this one:</p> <div class=highlight><pre><span></span><code><span id=__span-5-1><a id=__codelineno-5-1 name=__codelineno-5-1 href=#__codelineno-5-1></a>The connection to the server localhost:8080 was refused - did you specify the right host or port?
</span></code></pre></div> <p>That will happen in case you did not set up the kubectl parameters as specified in Prerequisites No. 3. You will now set it up for access to <em>dockerstate</em>:</p> <div class=highlight><pre><span></span><code><span id=__span-6-1><a id=__codelineno-6-1 name=__codelineno-6-1 href=#__codelineno-6-1></a>mkdir dockerspacedir
</span><span id=__span-6-2><a id=__codelineno-6-2 name=__codelineno-6-2 href=#__codelineno-6-2></a>
</span><span id=__span-6-3><a id=__codelineno-6-3 name=__codelineno-6-3 href=#__codelineno-6-3></a>openstack coe cluster config
</span><span id=__span-6-4><a id=__codelineno-6-4 name=__codelineno-6-4 href=#__codelineno-6-4></a>--dir dockerspacedir
</span><span id=__span-6-5><a id=__codelineno-6-5 name=__codelineno-6-5 href=#__codelineno-6-5></a>--force
</span><span id=__span-6-6><a id=__codelineno-6-6 name=__codelineno-6-6 href=#__codelineno-6-6></a>--output-certs
</span><span id=__span-6-7><a id=__codelineno-6-7 name=__codelineno-6-7 href=#__codelineno-6-7></a>dockerspace
</span></code></pre></div> <p>First create a new directory, <em>dockerspacedir</em>, where the config file for access to the cluster will reside, then execute the <strong>cluster config</strong> command. The output will be a line like this:</p> <div class=highlight><pre><span></span><code><span id=__span-7-1><a id=__codelineno-7-1 name=__codelineno-7-1 href=#__codelineno-7-1></a>export KUBECONFIG=/Users/duskosavic/3EnginesDocs/dockerspacedir/config
</span></code></pre></div> <p>Copy it and enter again as the command in terminal. That will give <strong>kubectl</strong> app access to the cluster. Create the pod with this command:</p> <div class=highlight><pre><span></span><code><span id=__span-8-1><a id=__codelineno-8-1 name=__codelineno-8-1 href=#__codelineno-8-1></a>kubectl apply -f redis.yaml
</span></code></pre></div> <p>It will read parameters in <em>redis.yaml</em> file and send them to the cluster.</p> <p>Here is the command to access all pods, if any:</p> <div class=highlight><pre><span></span><code><span id=__span-9-1><a id=__codelineno-9-1 name=__codelineno-9-1 href=#__codelineno-9-1></a>kubectl get pods
</span><span id=__span-9-2><a id=__codelineno-9-2 name=__codelineno-9-2 href=#__codelineno-9-2></a>
</span><span id=__span-9-3><a id=__codelineno-9-3 name=__codelineno-9-3 href=#__codelineno-9-3></a>NAME READY STATUS RESTARTS AGE
</span><span id=__span-9-4><a id=__codelineno-9-4 name=__codelineno-9-4 href=#__codelineno-9-4></a>redis 0/1 ContainerCreating 0 7s
</span></code></pre></div> <p>Repeat the command after a few seconds and see the difference:</p> <div class=highlight><pre><span></span><code><span id=__span-10-1><a id=__codelineno-10-1 name=__codelineno-10-1 href=#__codelineno-10-1></a>kubectl get pods
</span><span id=__span-10-2><a id=__codelineno-10-2 name=__codelineno-10-2 href=#__codelineno-10-2></a>
</span><span id=__span-10-3><a id=__codelineno-10-3 name=__codelineno-10-3 href=#__codelineno-10-3></a>NAME READY STATUS RESTARTS AGE
</span><span id=__span-10-4><a id=__codelineno-10-4 name=__codelineno-10-4 href=#__codelineno-10-4></a>redis 1/1 Running 0 81s
</span></code></pre></div> <p>In this step, you have created a new pod on cluster <em>dockerspace</em> and it is running.</p> <p>In the next step, you will enter the container and start issuing commands just like you would in any other Linux environment.</p> <h2 id=step-4-executing-bash-commands-in-the-container>Step 4 - Executing <em>bash</em> Commands in the Container<a href=#step-4-executing-bash-commands-in-the-container title="Permalink to this headline">🔗</a><a class=headerlink href=#step-4-executing-bash-commands-in-the-container title="Permanent link">&para;</a></h2> <p>In this step, you will start <strong>bash</strong> shell in the container, which in Linux is equivalent to start running the operating system:</p> <div class=highlight><pre><span></span><code><span id=__span-11-1><a id=__codelineno-11-1 name=__codelineno-11-1 href=#__codelineno-11-1></a>kubectl exec -it redis -- /bin/bash
</span></code></pre></div> <p>The following listing is a reply:</p> <div class=highlight><pre><span></span><code><span id=__span-12-1><a id=__codelineno-12-1 name=__codelineno-12-1 href=#__codelineno-12-1></a>root@redis:/data# df -h
</span><span id=__span-12-2><a id=__codelineno-12-2 name=__codelineno-12-2 href=#__codelineno-12-2></a>Filesystem Size Used Avail Use% Mounted on
</span><span id=__span-12-3><a id=__codelineno-12-3 name=__codelineno-12-3 href=#__codelineno-12-3></a>overlay 50G 1.4G 49G 3% /
</span><span id=__span-12-4><a id=__codelineno-12-4 name=__codelineno-12-4 href=#__codelineno-12-4></a>tmpfs 64M 0 64M 0% /dev
</span><span id=__span-12-5><a id=__codelineno-12-5 name=__codelineno-12-5 href=#__codelineno-12-5></a>tmpfs 3.9G 0 3.9G 0% /sys/fs/cgroup
</span><span id=__span-12-6><a id=__codelineno-12-6 name=__codelineno-12-6 href=#__codelineno-12-6></a>/dev/vdb 50G 1.4G 49G 3% /data
</span><span id=__span-12-7><a id=__codelineno-12-7 name=__codelineno-12-7 href=#__codelineno-12-7></a>/dev/vda4 32G 4.6G 27G 15% /etc/hosts
</span><span id=__span-12-8><a id=__codelineno-12-8 name=__codelineno-12-8 href=#__codelineno-12-8></a>shm 64M 0 64M 0% /dev/shm
</span><span id=__span-12-9><a id=__codelineno-12-9 name=__codelineno-12-9 href=#__codelineno-12-9></a>tmpfs 3.9G 16K 3.9G 1% /run/secrets/kubernetes.io/serviceaccount
</span><span id=__span-12-10><a id=__codelineno-12-10 name=__codelineno-12-10 href=#__codelineno-12-10></a>tmpfs 3.9G 0 3.9G 0% /proc/acpi
</span><span id=__span-12-11><a id=__codelineno-12-11 name=__codelineno-12-11 href=#__codelineno-12-11></a>tmpfs 3.9G 0 3.9G 0% /proc/scsi
</span><span id=__span-12-12><a id=__codelineno-12-12 name=__codelineno-12-12 href=#__codelineno-12-12></a>tmpfs 3.9G 0 3.9G 0% /sys/firmware
</span></code></pre></div> <p>This is what it would look like in the terminal:</p> <p><a class=glightbox href=../_images/redis-data.png data-type=image data-width=100% data-height=auto data-desc-position=bottom><img alt=redis-data.png src=../_images/redis-data.png></a></p> <p>Note that the prompt changed to</p> <div class=highlight><pre><span></span><code><span id=__span-13-1><a id=__codelineno-13-1 name=__codelineno-13-1 href=#__codelineno-13-1></a>root@redis:/data#
</span></code></pre></div> <p>which means you are now issuing commands within the container itself. The pod operates as Fedora 33 and you can use <strong>df</strong> to see the volumes and their sizes. Command</p> <div class=highlight><pre><span></span><code><span id=__span-14-1><a id=__codelineno-14-1 name=__codelineno-14-1 href=#__codelineno-14-1></a>df -h
</span></code></pre></div> <p>lists sizes of files and directories in a human fashion (the usual meaning of parameter <strong>-h</strong> would be <em>Help</em>, while here it is short for <em>Human</em>).</p> <p>In this step, you have activated the container operating system.</p> <h2 id=step-5-saving-a-file-into-persistent-storage>Step 5 - Saving a File Into Persistent Storage<a href=#step-5-saving-a-file-into-persistent-storage title="Permalink to this headline">🔗</a><a class=headerlink href=#step-5-saving-a-file-into-persistent-storage title="Permanent link">&para;</a></h2> <p>In this step you are going to test the longevity of files on persistent storage. You will first</p> <blockquote> <ul> <li>save a file into the <em>/data/redis</em> directory, then</li> <li>kill the Redis process, which in turn will</li> <li>kill the container; finally, you will</li> <li>re-enter the pod,</li> </ul> </blockquote> <p>where you will find the file intact.</p> <p>Note that <strong>dev/vdb</strong> has 50 GB in size in the above listing and connect it to the column <strong>Attached To</strong> in the <strong>Volumes</strong> =&gt; <strong>Volumes</strong> listing:</p> <p><a class=glightbox href=../_images/devvdb.png data-type=image data-width=100% data-height=auto data-desc-position=bottom><img alt=devvdb.png src=../_images/devvdb.png></a></p> <p>In its own turn, it is tied to an instance:</p> <p><a class=glightbox href=../_images/instance.png data-type=image data-width=100% data-height=auto data-desc-position=bottom><img alt=instance.png src=../_images/instance.png></a></p> <p>That instance is injected into the container and – being an independent instance – acts as persistent storage to the pod.</p> <p>Create a file on the <em>redis</em> container:</p> <div class=highlight><pre><span></span><code><span id=__span-15-1><a id=__codelineno-15-1 name=__codelineno-15-1 href=#__codelineno-15-1></a>cd /data/redis/
</span><span id=__span-15-2><a id=__codelineno-15-2 name=__codelineno-15-2 href=#__codelineno-15-2></a>echo Hello &gt; test-file
</span></code></pre></div> <p>Install software to see the <strong>PID</strong> number of <em>Redis</em> process in the container</p> <div class=highlight><pre><span></span><code><span id=__span-16-1><a id=__codelineno-16-1 name=__codelineno-16-1 href=#__codelineno-16-1></a>apt-get update
</span><span id=__span-16-2><a id=__codelineno-16-2 name=__codelineno-16-2 href=#__codelineno-16-2></a>apt-get install procps
</span><span id=__span-16-3><a id=__codelineno-16-3 name=__codelineno-16-3 href=#__codelineno-16-3></a>ps aux
</span></code></pre></div> <p>These are the running processes:</p> <p><a class=glightbox href=../_images/redis_kill.png data-type=image data-width=100% data-height=auto data-desc-position=bottom><img alt=redis_kill.png src=../_images/redis_kill.png></a></p> <p>Take the <strong>PID</strong> number for <em>Redis</em> process (here it is <strong>1</strong>), and eliminate it with command</p> <div class=highlight><pre><span></span><code><span id=__span-17-1><a id=__codelineno-17-1 name=__codelineno-17-1 href=#__codelineno-17-1></a>kill 1
</span></code></pre></div> <p>That will first kill the container and then exit its command line.</p> <p>In this step, you have created a file and killed the container that contains the file. This sets up the ground for testing whether the files survive container crash.</p> <h2 id=step-6-check-the-file-saved-in-previous-step>Step 6 - Check the File Saved in Previous Step<a href=#step-6-check-the-file-saved-in-previous-step title="Permalink to this headline">🔗</a><a class=headerlink href=#step-6-check-the-file-saved-in-previous-step title="Permanent link">&para;</a></h2> <p>In this step, you will find out whether the file <em>test-file</em> is still existing.</p> <p>Enter the pod again, activate its <strong>bash</strong> shell and see whether the file has survived:</p> <div class=highlight><pre><span></span><code><span id=__span-18-1><a id=__codelineno-18-1 name=__codelineno-18-1 href=#__codelineno-18-1></a>kubectl exec -it redis -- /bin/bash
</span><span id=__span-18-2><a id=__codelineno-18-2 name=__codelineno-18-2 href=#__codelineno-18-2></a>cd redis
</span><span id=__span-18-3><a id=__codelineno-18-3 name=__codelineno-18-3 href=#__codelineno-18-3></a>ls
</span><span id=__span-18-4><a id=__codelineno-18-4 name=__codelineno-18-4 href=#__codelineno-18-4></a>
</span><span id=__span-18-5><a id=__codelineno-18-5 name=__codelineno-18-5 href=#__codelineno-18-5></a>test-file
</span></code></pre></div> <p>Yes, the file <em>test-file</em> is still there. The persistent storage for the pod contains it in path <em>/data/redis</em>:</p> <p><a class=glightbox href=../_images/final_result.png data-type=image data-width=100% data-height=auto data-desc-position=bottom><img alt=final_result.png src=../_images/final_result.png></a></p> <p>In this step, you have entered the pod again and found out that the file has survived intact. That was expected, as volumes of type <em>emptyDir</em> will survive container crashes as long as the pod is existing.</p> <h2 id=what-to-do-next>What To Do Next<a href=#what-to-do-next title="Permalink to this headline">🔗</a><a class=headerlink href=#what-to-do-next title="Permanent link">&para;</a></h2> <p><em>emptyDir</em> survives container crashes but will disappear when the pod disappears. Other volume types may survive loss of pods better. For instance:</p> <blockquote> <ul> <li><em>awsElasticBlockStore</em> will have the volume unmounted when the pod is gone; being unmounted and not destroyed, it will persist the data it is containing. This type of volume can have pre-populated data and can share the data among the pods.</li> <li><em>cephfs</em> can also have pre-populated data and share them among the pods, but can additionally also be mounted by multiple writers at the same time.</li> </ul> </blockquote> <p>Other constraints may also apply. Some of those volume types will require their own servers to be activated first, or that all nodes on which Pods are running need be of the same type and so on. Prerequisite No. 6 will list all types of volumes for Kubernetes clusters so study it and apply to your own Kubernetes apps.</p> </article> </div> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> Made with <a href=https://squidfunk.github.io/mkdocs-material/ target=_blank rel=noopener> Material for MkDocs </a> </div> </div> </div> </footer> </div> <div class=md-dialog data-md-component=dialog> <div class="md-dialog__inner md-typeset"></div> </div> <script id=__config type=application/json>{"base": "..", "features": ["content.code.annotate", "content.code.copy", "content.tooltips", "navigation.tabs", "navigation.sections", "navigation.footer", "navigation.indexes", "navigation.sections", "navigation.top", "navigation.tracking", "search.highlight", "search.share", "search.suggest", "toc.follow"], "search": "../assets/javascripts/workers/search.d50fe291.min.js", "tags": null, "translations": {"clipboard.copied": "Copied to clipboard", "clipboard.copy": "Copy to clipboard", "search.result.more.one": "1 more on this page", "search.result.more.other": "# more on this page", "search.result.none": "No matching documents", "search.result.one": "1 matching document", "search.result.other": "# matching documents", "search.result.placeholder": "Type to start searching", "search.result.term.missing": "Missing", "select.version": "Select version"}, "version": null}</script> <script src=../assets/javascripts/bundle.13a4f30d.min.js></script> <script id="init-glightbox">const lightbox = GLightbox({"touchNavigation": false, "loop": false, "zoomable": true, "draggable": true, "openEffect": "zoom", "closeEffect": "zoom", "slideEffect": "slide"});
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