instruction: Explain Kubernetes Object Management
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  Kubernetes Object Management
  kubectl
  command-line tool supports several different ways to create and manage
  Kubernetes
  objects
  . This document provides an overview of the different
  approaches. Read the
  Kubectl book
  details of managing objects by Kubectl.
  Management techniques
  Warning:
  A Kubernetes object should be managed using only one technique. Mixing
  and matching techniques for the same object results in  behavior.
  Management technique
  Operates on
  Recommended environment
  Supported writers
  Learning curve
  Imperative commands
  Live objects
  Development projects
  Lowest
  Imperative object configuration
  Individual files
  Production projects
  Moderate
  Declarative object configuration
  Directories of files
  Production projects
  Highest
  Imperative commands
  When using imperative commands, a user operates directly on live objects
  in a cluster. The user provides operations to
  kubectl
  command as arguments or flags.
  This is the recommended way to get started or to run a one-off task in
  a cluster. Because this technique operates directly on live
  objects, it provides no history of previous configurations.
  Examples
  Run an instance of the nginx container by creating a Deployment object:
  kubectl create deployment nginx --image nginx
  Trade-offs
  Advantages compared to object configuration:
  Commands are expressed as a single action word.
  Commands require only a single step to make changes to the cluster.
  Disadvantages compared to object configuration:
  Commands do not integrate with change review processes.
  Commands do not provide an audit trail associated with changes.
  Commands do not provide a source of records except for what is live.
  Commands do not provide a template for creating new objects.
  Imperative object configuration
  In imperative object configuration, the kubectl command specifies the
  operation (create, replace, etc.), optional flags and at least one file
  name. The file specified must contain a full definition of the object
  in YAML or JSON format.
  See the
  API reference
  for more details on object definitions.
  Warning:
  The imperative
  replace
  command replaces the existing
  spec with the newly provided one, dropping all changes to the object missing from
  the configuration file. This approach should not be used with resource
  types whose specs are updated independently of the configuration file.
  Services of type
  LoadBalancer
  , for example, have their
  externalIPs
  field updated
  independently from the configuration by the cluster.
  Examples
  Create the objects defined in a configuration file:
  kubectl create -f nginx.yaml
  Delete the objects defined in two configuration files:
  kubectl delete -f nginx.yaml -f redis.yaml
  Update the objects defined in a configuration file by overwriting
  the live configuration:
  kubectl replace -f nginx.yaml
  Trade-offs
  Advantages compared to imperative commands:
  Object configuration can be stored in a source control system such as Git.
  Object configuration can integrate with processes such as reviewing changes before push and audit trails.
  Object configuration provides a template for creating new objects.
  Disadvantages compared to imperative commands:
  Object configuration requires basic understanding of the object schema.
  Object configuration requires the additional step of writing a YAML file.
  Advantages compared to declarative object configuration:
  Imperative object configuration behavior is simpler and easier to understand.
  As of Kubernetes version 1.5, imperative object configuration is more mature.
  Disadvantages compared to declarative object configuration:
  Imperative 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.
  Declarative object configuration
  When using declarative object configuration, a user operates on object
  configuration files stored locally, however the user does not define the
  operations to be taken on the files. Create, update, and delete operations
  are automatically detected per-object by
  kubectl
  . This enables working on
  directories, where different operations might be needed for different objects.
  Note:
  Declarative object configuration retains changes made by other
  writers, even if the changes are not merged back to the object configuration file.
  This is possible by using the
  patch
  API operation to write only
  observed differences, instead of using the
  replace
  API operation to replace the entire object configuration.
  Examples
  Process all object configuration files in the
  configs
  directory, and create or
  patch the live objects. You can first
  diff
  to see what changes are going to be
  made, and then apply:
  kubectl diff -f configs/
  kubectl apply -f configs/
  Recursively process directories:
  kubectl diff -R -f configs/
  kubectl apply -R -f configs/
  Trade-offs
  Advantages compared to imperative object configuration:
  Changes made directly to live objects are retained, even if they are not merged back into the configuration files.
  Declarative object configuration has better support for operating on directories and automatically detecting operation types (create, patch, delete) per-object.
  Disadvantages compared to imperative object configuration:
  Declarative object configuration is harder to debug and understand results when they are unexpected.
  Partial updates using diffs create complex merge and patch operations.
  What's next
  Managing Kubernetes Objects Using Imperative Commands
  Imperative Management of Kubernetes Objects Using Configuration Files
  Declarative Management of Kubernetes Objects Using Configuration Files
  Declarative Management of Kubernetes Objects Using Kustomize
  Kubectl Command Reference
  Kubectl Book
  Kubernetes API Reference
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  Last modified January 08, 2022 at 6:09 PM PST:
  Reorganize Working with Kubernetes Objects section (634c17f61c)