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cmd/config: Add examples and tutorials for config functions
- Add examples under `functions` - Add built-in tutorial for functions
This commit is contained in:
Phillip Wittrock
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cmd/config/docs/tutorials/function-basics.md
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184
cmd/config/docs/tutorials/function-basics.md
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## Function Basics
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### Synopsis
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`kustomize config` enables encapsulating function for manipulating Resource
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configuration inside containers, which are run using `run-fns`.
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First fetch the kustomize repository, which contains a collection of example
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functions
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git clone https://github.com/kubernetes-sigs/kustomize
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cd kustomize/functions/examples/
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### Templating -- CockroachDB
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This section demonstrates how to leverage templating based solutions from
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`kustomize config`. The templating function is implemented as a `bash` script
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using a `heredoc`.
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#### 1: Generate the Resources
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`cd` into the `kustomize/functions/examples/template-heredoc-cockroachdb/`
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directory, and invoke `run-fns` on the `local-resource/` directory.
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cd template-heredoc-cockroachdb/
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# view the Resources
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kustomize config tree local-resource/ --name --image --replicas
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# run the function
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kustomize config run-fns local-resource/
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# view the generated Resources
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kustomize config tree local-resource/ --name --image --replicas
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`run-fns` generated the directory ` local-resource/config` containing the generated
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Resources.
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#### 2. Modify the Generated Resources
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- modify the generated Resources by adding an annotation, sidecar container, etc.
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- modify the `local-resources/example-use.yaml` by changing the replicas
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re-run `run-fns`. this will apply the updated replicas to the generated Resources,
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but keep the fields that you manually added to the generated Resource configuration.
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# run the function
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kustomize config run-fns local-resource/
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`run-fns` facilitates a non-destructive *smart templating* approach that allows templating
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to be composed with manual modifications directly to the template output, as well as
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composition with other functions which may appy validation or injection of values.
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#### 3. Function Implementation
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the function implementation is located under the `image/` directory as a `Dockerfile`
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and a `bash` script.
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### Templating -- Nginx
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The steps in this section are identical to the CockroachDB templating example,
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but the function implementation is very different, and implemented as a `go`
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program rather than a `bash` script.
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#### 1: Generate the Resources
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`cd` into the `kustomize/functions/examples/template-go-nginx/`
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directory, and invoke `run-fns` on the `local-resource/` directory.
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cd template-go-nginx/
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# view the Resources
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kustomize config tree local-resource/ --name --image --replicas
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# run the function
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kustomize config run-fns local-resource/
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# view the generated Resources
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kustomize config tree local-resource/ --name --image --replicas
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`run-fns` generated the directory ` local-resource/config` containing the generated
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Resources. this time it put the configuration in a single file rather than multiple
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files. The mapping of Resources to files is controlled by the function itself through
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annotations on the generated Resources.
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#### 2. Modify the Generated Resources
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- modify the generated Resources by adding an annotation, sidecar container, etc.
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- modify the `local-resources/example-use.yaml` by changing the replicas
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re-run `run-fns`. this will apply the updated replicas to the generated Resources,
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but keep the fields that you manually added to the generated Resource configuration.
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# run the function
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kustomize config run-fns local-resource/
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Just like in the preceding section, the function is implemented using a non-destructive
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approach which merges the generated Resources into previously generated instances.
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#### 3. Function Implementation
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the function implementation is located under the `image/` directory as a `Dockerfile`
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and a `go` program.
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### Validation -- resource reservations
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This section uses `run-fns` to perform validation rather than generate Resources.
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#### 1: Run the Validator
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`cd` into the `kustomize/functions/examples/validator-resource-requests`
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directory, and invoke `run-fns` on the `local-resource/` directory.
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# run the function
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kustomize config run-fns local-resource/
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cpu-requests missing for a container in Deployment nginx (example-use.yaml [1])
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Error: exit status 1
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Usage:
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...
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#### 2: Fix the validation issue
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The command will fail complaining that the nginx Deployment is missing `cpu-requests`,
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and print the name of the file + Resource index. Edit the file and uncomment the resources,
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then re-run the functions.
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kustomize config run-fns local-resource/
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The validation now passes.
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### Injection -- resource reservations
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This section uses `run-fns` to perform injection of field values based off annotations
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on the Resource.
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#### 1: Run the Injector
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`cd` into the `kustomize/functions/examples/inject-tshirt-sizes`
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directory, and invoke `run-fns` on the `local-resource/` directory.
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# print the resources
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kustomize config tree local-resource --resources --name
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local-resource
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├── [example-use.yaml] Validator
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└── [example-use.yaml] Deployment nginx
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└── spec.template.spec.containers
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└── 0
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└── name: nginx
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# run the functions
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kustomize config run-fns local-resource/
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# print the new resources
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kustomize config tree local-resource --resources --name
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├── [example-use.yaml] Validator
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└── [example-use.yaml] Deployment nginx
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└── spec.template.spec.containers
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└── 0
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├── name: nginx
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└── resources: {requests: {cpu: 4, memory: 1GiB}}
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#### 2: Change the tshirt-size
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Change the `tshirt-size` annotation from `medium` to `small` and re-run the functions.
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kustomize config run-fns local-resource/
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kustomize config tree local-resource/
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local-resource
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├── [example-use.yaml] Validator
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└── [example-use.yaml] Deployment nginx
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└── spec.template.spec.containers
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└── 0
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├── name: nginx
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└── resources: {requests: {cpu: 200m, memory: 50MiB}}
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The function has applied the reservations for the new tshirt-size
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### Function Composition
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Functions may be composed together. Try putting the Injection (tshirt-size) and
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Validation functions together in the same .yaml file (separated by `---`). Run
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`run-fns` and observe that the first function in the file is applied to the Resources,
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and then the second function in the file is applied.
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