kubectl apply vs kubectl create

Question

What I understood by the documentation is that    kubectl create   Creates a new k8s resource in the cluster kubectl replace   Updates a resource in the live cluster kubectl apply   If I want to do create   replace  Reference    My questions are   Why are there three operations for doing the same task in a cluster  What are the use cases for these operations  How do they differ from each other under the hood

User · Answer

One for the finest way to understand the difference for beginner     Ref   https   www digitalocean com community tutorials imperative-vs-declarative-kubernetes-management-a-digitalocean-comic

User · Answer

Those are two different approaches   Imperative Management  kubectl create is what we call Imperative Management  On this approach you tell the Kubernetes API what you want to create  replace or delete  not how you want your K8s cluster world to look like   Declarative Management  kubectl apply is part of the Declarative Management approach  where changes that you may have applied to a live object  i e  through scale  are  maintained  even if you apply other changes to the object      You can read more about imperative and declarative management in the Kubernetes Object Management documentation

User · Answer

These are imperative commands   kubectl run   kubectl create deployment Advantages   Simple  easy to learn and easy to remember  Require only a single step to make changes to the cluster   Disadvantages   Do not integrate with change review processes  Do not provide an audit trail associated with changes  Do not provide a source of records except for what is live  Do not provide a template for creating new objects   These are imperative object config  kubectl create -f your-object-config yaml kubectl delete -f your-object-config yaml kubectl replace -f your-object-config yaml Advantages compared to imperative commands   Can be stored in a source control system such as Git  Can integrate with processes such as reviewing changes before push and audit trails  Provides a template for creating new objects   Disadvantages compared to imperative commands   Requires basic understanding of the object schema  Requires the additional step of writing a YAML file   Advantages compared to declarative object config   Simpler and easier to understand  More mature after Kubernetes version 1 5   Disadvantages compared to declarative object configuration   Works best on files  not directories  Updates to live objects must be reflected in configuration files  or they will be lost during the next replacement   These are declarative object config kubectl diff -f configs  kubectl apply -f configs  Advantages compared to imperative object config   Changes made directly to live objects are retained  even if they are not merged back into the configuration files  Better support for operating on directories and automatically detecting operation types  create  patch  delete  per-object   Disadvantages compared to imperative object configuration   Harder to debug and understand results when they are unexpected  Partial updates using diffs create complex merge and patch operations

User · Answer

We love Kubernetes is because once we give them what we want it goes on to figure out how to achieve it without our any involvement     create  is like playing GOD by taking things into our own hands  It is good for local debugging when you only want to work with the POD and not care abt Deployment Replication Controller     apply  is playing by the rules   apply  is like a master tool that helps you create and modify and requires nothing from you to manage the pods

User · Answer

kubectl  create can work with one object configuration file at a time  This is also known as imperative management  kubectl create -f filename url  kubectl  apply works with directories and its sub directories containing object configuration yaml files  This is also known as  declarative management  Multiple object configuration files from directories can be picked up  kubectl apply -f directory   Details     https   kubernetes io docs tasks manage-kubernetes-objects declarative-config    https   kubernetes io docs tasks manage-kubernetes-objects imperative-config

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----------------------------------------------------------     command    object does not exist    object already exists      --------- ----------------------- ------------------------      create     create new object                 ERROR                                                                                 apply      create new object        configure object                         needs complete spec      accepts partial spec                                                                         replace            ERROR            delete object                                                    create new object          ----------------------------------------------------------

User · Answer

Just to give a more straight forward answer  from my understanding   apply - makes incremental changes to an existing object  create - creates a whole new object  previously non-existing   deleted   Taking this from a DigitalOcean article which was linked by Kubernetes website      We use apply instead of create here so that in the future we can incrementally apply changes to the Ingress Controller objects instead of completely overwriting them

User · Answer

The explanation below from the official documentation helped me understand kubectl apply       This command will compare the version of the configuration that you   re pushing with the previous version and apply the changes you   ve made  without overwriting any automated changes to properties you haven   t specified    kubectl create on the other hand will create  should be non-existing  resources

User · Answer

When running in a CI script  you will have trouble with imperative commands as create raises an error if the resource already exists   What you can do is applying  declarative pattern  the output of your imperative command  by using --dry-run true and -o yaml options   kubectl create whatever --dry-run true -o yaml   kubectl apply -f -   The command above will not raise an error if the resource already exists  and will update the resource if needed    This is very useful in some cases where you cannot use the declarative pattern  for instance when creating a docker-registry secret

[kubernetes] kubectl apply vs kubectl create?

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