Template GoTemplate

This is an example of implementing a template function using a go template.

This example uses a more sophisticated approach for building abstractions.

Function implementation

The function is implemented as an image, and built using make image.

The template is implemented as a go program with a go template. It parses the functionConfig into a go struct and uses the kyaml module for parsing the function input, and writing the function output.

1. read the inputs (stdin)
2. apply filters

• (custom filter) generate the nginx Deployment and Service from go templates using the functionConfig as the template input.
• merge the generated Deployment and Service with the input Deployment and Service if present
• set filenames on the Resources (NAME.yaml)
• format the Resources

3. write the outputs (stdout)

Function invocation

The function is invoked by authoring a local Resource with metadata.annotations.[config.kubernetes.io/function] and running:

kustomize fn run local-resource/

This generates the local-resource/config directory containing the template output.

• the template output may be modified by adding fields -- such as initContainers, sidecarConatiners, cpu resource limits, etc -- and these fields will be retained when re-running run
• the function input example-use.yaml may be changed and rerunning run will update only the parts changed in the template output.

Running the Example

Run the config with:

kustomize build --enable-alpha-plugins local-resource/

This will create the directory

local-resource/config

Add an annotation to the Deployment Resource and change the replica count of the kind: Nginx Resource in example-use.yaml. Rerun the template:

kustomize build --enable-alpha-plugins local-resource/

The replica count should be updated, but your annotation should remain.