{"id":400737,"date":"2022-01-28T17:45:05","date_gmt":"2022-01-28T14:45:05","guid":{"rendered":"https:\/\/en.buradabiliyorum.com\/declarative-vs-imperative-kubernetes-object-management-cloudsavvy-it\/"},"modified":"2022-01-28T17:45:05","modified_gmt":"2022-01-28T14:45:05","slug":"declarative-vs-imperative-kubernetes-object-management-cloudsavvy-it","status":"publish","type":"post","link":"https:\/\/buradabiliyorum.com\/en\/declarative-vs-imperative-kubernetes-object-management-cloudsavvy-it\/","title":{"rendered":"#Declarative vs Imperative Kubernetes Object Management \u2013 CloudSavvy IT"},"content":{"rendered":"<div id=\"ez-toc-container\" class=\"ez-toc-v2_0_84 counter-hierarchy ez-toc-counter ez-toc-custom ez-toc-container-direction\">\n<p class=\"ez-toc-title\" style=\"cursor:inherit\">Table of Contents<\/p>\n<label for=\"ez-toc-cssicon-toggle-item-6a2dd8510067d\" class=\"ez-toc-cssicon-toggle-label\"><span class=\"\"><span class=\"eztoc-hide\" style=\"display:none;\">Toggle<\/span><span class=\"ez-toc-icon-toggle-span\"><svg style=\"fill: #dd3333;color:#dd3333\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" class=\"list-377408\" width=\"20px\" height=\"20px\" viewBox=\"0 0 24 24\" fill=\"none\"><path d=\"M6 6H4v2h2V6zm14 0H8v2h12V6zM4 11h2v2H4v-2zm16 0H8v2h12v-2zM4 16h2v2H4v-2zm16 0H8v2h12v-2z\" fill=\"currentColor\"><\/path><\/svg><svg style=\"fill: #dd3333;color:#dd3333\" class=\"arrow-unsorted-368013\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"10px\" height=\"10px\" viewBox=\"0 0 24 24\" version=\"1.2\" baseProfile=\"tiny\"><path d=\"M18.2 9.3l-6.2-6.3-6.2 6.3c-.2.2-.3.4-.3.7s.1.5.3.7c.2.2.4.3.7.3h11c.3 0 .5-.1.7-.3.2-.2.3-.5.3-.7s-.1-.5-.3-.7zM5.8 14.7l6.2 6.3 6.2-6.3c.2-.2.3-.5.3-.7s-.1-.5-.3-.7c-.2-.2-.4-.3-.7-.3h-11c-.3 0-.5.1-.7.3-.2.2-.3.5-.3.7s.1.5.3.7z\"\/><\/svg><\/span><\/span><\/label><input type=\"checkbox\"  id=\"ez-toc-cssicon-toggle-item-6a2dd8510067d\" checked aria-label=\"Toggle\" \/><nav><ul class='ez-toc-list ez-toc-list-level-1 ' ><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-1\" href=\"https:\/\/buradabiliyorum.com\/en\/declarative-vs-imperative-kubernetes-object-management-cloudsavvy-it\/#Declarative_vs_Imperative_Definitions\" >Declarative vs Imperative: Definitions<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-2\" href=\"https:\/\/buradabiliyorum.com\/en\/declarative-vs-imperative-kubernetes-object-management-cloudsavvy-it\/#Managing_Objects_Imperatively\" >Managing Objects Imperatively<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-3\" href=\"https:\/\/buradabiliyorum.com\/en\/declarative-vs-imperative-kubernetes-object-management-cloudsavvy-it\/#Trying_Declarative_Management\" >Trying Declarative Management<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-4\" href=\"https:\/\/buradabiliyorum.com\/en\/declarative-vs-imperative-kubernetes-object-management-cloudsavvy-it\/#Declarative_vs_Imperative_Comparing_The_Trade-offs\" >Declarative vs Imperative: Comparing The Trade-offs<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-5\" href=\"https:\/\/buradabiliyorum.com\/en\/declarative-vs-imperative-kubernetes-object-management-cloudsavvy-it\/#Conclusion\" >Conclusion<\/a><\/li><\/ul><\/nav><\/div>\n<p><strong>&#8220;#Declarative vs Imperative Kubernetes Object Management \u2013 CloudSavvy IT&#8221;<\/strong><\/p>\n<div id=\"article-content-area\">\n<figure style=\"width: 1200px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" class=\"type:primaryImage size-full wp-image-14588\" data-pagespeed-lazy-srcset=\"https:\/\/www.cloudsavvyit.com\/p\/uploads\/2021\/10\/c0e5b7df.png?width=398&amp;trim=1,1&amp;bg-color=000&amp;pad=1,1 400w, https:\/\/www.cloudsavvyit.com\/p\/uploads\/2021\/10\/c0e5b7df.png?width=1198&amp;trim=1,1&amp;bg-color=000&amp;pad=1,1 1200w\" sizes=\"auto, 400w, 1200w\" data-pagespeed-lazy-src=\"https:\/\/www.cloudsavvyit.com\/p\/uploads\/2021\/10\/c0e5b7df.png?width=1198&amp;trim=1,1&amp;bg-color=000&amp;pad=1,1\" alt=\"Illustration of the Kubernetes logo on a smartphone\" width=\"1200\" height=\"675\" src=\"\/pagespeed_static\/1.JiBnMqyl6S.gif\" onload=\"pagespeed.lazyLoadImages.loadIfVisibleAndMaybeBeacon(this);\" onerror=\"this.onerror=null;pagespeed.lazyLoadImages.loadIfVisibleAndMaybeBeacon(this);\"\/><figcaption class=\"wp-caption-text\"><span class=\"type:primaryImage imagecredit\"><a rel=\"nofollow noopener\" target=\"_blank\" href=\"https:\/\/www.shutterstock.com\/image-illustration\/kubernetes-symbol-on-smartphone-screen-white-1974756836\">o_m\/Shutterstock.com<\/a><\/span><\/figcaption><\/figure>\n<p>Kubernetes is usually described as a declarative system. Most of the time you work with YAML that defines what the end state of the system should look like. Kubernetes supports imperative APIs too though, where you issue a command and get an im<a href=\"https:\/\/buradabiliyorum.com\/en\/category\/social-mediaa\/\" data-internallinksmanager029f6b8e52c=\"1\" title=\"Social Media\" target=\"_blank\" rel=\"noopener\">media<\/a>te output.<\/p>\n<p>In this article, we\u2019ll explore the differences between these two <a rel=\"nofollow noopener\" target=\"_blank\" href=\"https:\/\/kubernetes.io\/docs\/concepts\/overview\/working-with-objects\/object-management\">forms of object management<\/a>. The chances are you\u2019ve already used both even if you don\u2019t recognize the terms.<\/p>\n<h2 id=\"declarative-vs-imperative-definitions\"><span class=\"ez-toc-section\" id=\"Declarative_vs_Imperative_Definitions\"><\/span>Declarative vs Imperative: Definitions<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p>First it\u2019s helpful to examine the terminology.<\/p>\n<p>Something that\u2019s <em>declarative<\/em> makes a statement of the end result, indicating intent but not the process to achieve it. In Kubernetes, this is saying \u201cThere should be a ReplicaSet with three Pods.\u201d<\/p>\n<p>An <em>imperative<\/em> acts as a command. Whereas a declarative is passive, imperatives are active and immediate: \u201cCreate a ReplicaSet with three Pods.\u201d<\/p>\n<p>The Kubernetes ecosystem provides mechanisms for interacting with your cluster in either of these forms. Imperative <a href=\"https:\/\/buradabiliyorum.com\/en\/category\/download-scripts-themes-apps\/\" data-internallinksmanager029f6b8e52c=\"9\" title=\"Download Scripts &amp; Themes &amp; Apps\" target=\"_blank\" rel=\"noopener\">app<\/a>roaches are catered for by CLI commands and individual YAML files. Declarative configuration is facilitated using directories of files that are combined into the final resource representation.<\/p>\n<h2 id=\"managing-objects-imperatively\"><span class=\"ez-toc-section\" id=\"Managing_Objects_Imperatively\"><\/span>Managing Objects Imperatively<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p>Here\u2019s an example of creating a Deployment imperatively:<\/p>\n<pre>kubectl create deployment my-deployment --image my-image:latest<\/pre>\n<p>You\u2019re instructing Kubernetes to immediately add a new Deployment to your cluster. The command includes a single verb (<code>create<\/code>) and the name of the resource type you\u2019re working with (<code>deployment<\/code>).<\/p>\n<p>You can also write a YAML file and apply it imperatively using the <code>create<\/code> command:<\/p>\n<div class=\"wp-geshi-highlight-wrap5\">\n<div class=\"wp-geshi-highlight-wrap4\">\n<div class=\"wp-geshi-highlight-wrap3\">\n<div class=\"wp-geshi-highlight-wrap2\">\n<div class=\"wp-geshi-highlight-wrap\">\n<div class=\"wp-geshi-highlight\">\n<div class=\"yaml\">\n<pre class=\"de1\"><span class=\"co3\">apiVersion<\/span><span class=\"sy2\">: <\/span>apps\/v1<span class=\"co3\">\nkind<\/span><span class=\"sy2\">: <\/span>Deployment<span class=\"co4\">\nspec<\/span>:<span class=\"co3\">\n  replicas<\/span><span class=\"sy2\">: <\/span>3<span class=\"co4\">\n  selector<\/span>:<span class=\"co4\">\n    matchLabels<\/span>:<span class=\"co3\">\n      app<\/span><span class=\"sy2\">: <\/span>example<span class=\"co4\">\n  template<\/span>:<span class=\"co4\">\n    metadata<\/span>:<span class=\"co4\">\n      labels<\/span>:<span class=\"co3\">\n        app<\/span><span class=\"sy2\">: <\/span>example<span class=\"co4\">\n    spec<\/span><span class=\"sy2\">:\n<\/span>        <span class=\"co1\"># ...<\/span><\/pre>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<pre>kubectl create -f deployment.yml<\/pre>\n<p>As before, you\u2019re issuing an immediate command via an active verb. Kubernetes will take the configuration from your file and create corresponding resources in the cluster. If you need to update a resource, you must modify your YAML and use the <code>replace<\/code> command to effect the change:<\/p>\n<pre>kubectl replace -f deployment.yml<\/pre>\n<p>This operation will <em>remove<\/em> the spec of any existing resources and replace it with the version in your config file. This is conveyed by the name of the <code>replace<\/code> command. It means you\u2019ll lose any changes made to your live objects that aren\u2019t present in your YAML.<\/p>\n<p>When Kubernetes is consuming imperative commands, it needs to be told exactly what to do. Consequently there\u2019s no way to selectively apply just the changed parts of your YAML. For that you\u2019ll need to switch to declarative operations.<\/p>\n<h2 id=\"trying-declarative-management\"><span class=\"ez-toc-section\" id=\"Trying_Declarative_Management\"><\/span>Trying Declarative Management<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p>Declarative management is only available when you\u2019re using YAML config files. There\u2019s no such thing as a declarative command. When you\u2019re using declarative operations, you don\u2019t tell Kubernetes what to do by providing a verb (<code>create<\/code>\/<code>replace<\/code>). Instead, you use the single <code>apply<\/code> command and trust Kubernetes to work out the actions to perform.<\/p>\n<pre>kubectl apply -f deployment.yml<\/pre>\n<p>Continuing the deployment example from above, <em>applying<\/em> the above YAML to your cluster would initially act the same as an imperative\u00a0 <code>create<\/code> command. No matching resource will exist to begin with so Kubernetes must create a new one.<\/p>\n<p>You could then change the <code>replicas<\/code> field to <code>5<\/code> and repeat the <code>apply<\/code> command. This time Kubernetes will match the existing resource, detect the change in your YAML, and scale the deployment without impacting any other fields.<\/p>\n<p>Using the imperative approach, you\u2019d need to use the <a rel=\"nofollow noopener\" target=\"_blank\" href=\"https:\/\/kubernetes.io\/docs\/reference\/kubectl\/cheatsheet\"><code>kubectl scale<\/code><\/a> command to change the replica count of an existing deployment. If you modified the YAML you used with <code>kubectl create<\/code>, you\u2019d need to run <code>kubectl replace<\/code> \u2013 but this would replace the deployment\u2019s entire <code>spec<\/code>, instead of simply scaling its replica count.<\/p>\n<h2 id=\"declarative-vs-imperative-comparing-the-trade-offs\"><span class=\"ez-toc-section\" id=\"Declarative_vs_Imperative_Comparing_The_Trade-offs\"><\/span>Declarative vs Imperative: Comparing The Trade-offs<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p><a rel=\"nofollow noopener\" target=\"_blank\" href=\"https:\/\/kubernetes.io\/docs\/tasks\/manage-kubernetes-objects\/imperative-command\">Imperative operations<\/a> are simple to understand and reason about. Each action is expressed as a verb with a clearly defined consequence. For this reason, most people will begin their earliest Kubernetes interactions using imperative commands that can be loosely mapped to other technologies such as Docker.<\/p>\n<p>Declarative management exposes the real power of Kubernetes. You declare what the final state should look like, then let Kubernetes do the rest. Every command has the same imperative action \u2013 <code>apply<\/code> this set of YAML files and progress the cluster to the state they define.<\/p>\n<p><a rel=\"nofollow noopener\" target=\"_blank\" href=\"https:\/\/kubernetes.io\/docs\/tasks\/manage-kubernetes-objects\/declarative-config\">Declarative management<\/a> is ideal for automated deployments. You don\u2019t need to spend time crafting a set of migration instructions each time you update a resource. Instead, adjust your YAML so it would produce correctly configured objects if they were created anew at the present time. Kubernetes will handle updates of existing objects so they match the new state too.<\/p>\n<p>Declarative YAML files are easy to version, review, and merge as part of your source control system. If you use imperative commands, you\u2019ve got no way of tracking how your cluster has evolved and it\u2019ll be trickier to rollback to an earlier state. Unlike imperative operations, declarative updates don\u2019t overwrite the entire object so you\u2019ll retain changes you made through other mechanisms, independently of your YAML files.<\/p>\n<p>Nonetheless imperative management does retain some advantages. Declarative configuration adds layers of complexity and can be harder to debug, particularly when Kubernetes selects an unexpected course of action. Each change results in a merge and patch operation to bring your objects into alignment with your desired state. With the imperative model, what you ask for is what you\u2019ll get, unless an error occurs.<\/p>\n<p>As ever when two approaches are offered, both strategies are useful and which you choose should depend on the context. For production clusters hosting live apps with frequent changes, you probably want versioned declarative YAML files. If you\u2019re quickly spinning up new containers in a development cluster, imperative commands will save time and be easier to work with.<\/p>\n<h2 id=\"conclusion\"><span class=\"ez-toc-section\" id=\"Conclusion\"><\/span>Conclusion<span class=\"ez-toc-section-end\"><\/span><\/h2>\n<p>Declarative and imperative management are two ways of interacting with your Kubernetes cluster and its resources. Kubectl has integrated support for both these strategies but the techniques shouldn\u2019t be mixed on a per-object basis. If you create an object declaratively, it should be managed that way through its entire life \u2013 using imperative commands with it can lead to unexpected behavior.<\/p>\n<p>Imperative operations affect live objects within your cluster. You define a verb, resource, and configuration via command arguments and flags. Declarative management is based on changes to local config files that Kubectl diffs and applies to the cluster via patches when you use the <code>kubectl diff<\/code> and <code>kubectl apply<\/code> commands.\n<\/div>\n<blockquote><p><strong><span style=\"color: #ff6600;\">If you liked the article, do not forget to share it with your friends. 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Most of the time you work with YAML that defines what the end state of the system should look like. Kubernetes supports imperative APIs too though, where you issue a command and get an immediate output. 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