Set field values
Dynamic needs for packages are built into tools which read and write configuration data.
Topics
Kpt packages can be modified using existing tools and workflows such as manually modifying the configuration in an editor, however these workflows can be labor intensive and error prone.
To address the UX limitations of hand editing YAML, kpt provides built-in commands which expose setting values in a user friendly way from the commandline.
Rather than exposing values as input parameters to a template, commands modify the package data in place.
These commands are defined per-package through OpenAPI definitions which are part of the package metadata – i.e. the [Kptfile].
While OpenAPI is often used to define schema for static types (e.g. this is what a Deployment looks like), kpt uses OpenAPI to define schema for individual instances of a type as well (e.g. this is what the nginx Deployment looks like).
To see more on how to create a setter: create setter guide
Setters explained
Following is a short explanation of the command that will be demonstrated in this guide.
Data model
- Fields reference setters through OpenAPI definitions specified as
line comments – e.g.
# { "$kpt-set": "replicas-setter" } - OpenAPI definitions are provided through the Kptfile
Command control flow
- Read the package Kptfile and resources.
- Change the setter OpenAPI value in the Kptfile
- Locate all fields which reference the setter and change their values.
- Write both the modified Kptfile and resources back to the package.
Steps
Fetch a remote package
Command
export SRC_REPO=https://github.com/GoogleContainerTools/kpt.git
kpt pkg get $SRC_REPO/package-examples/helloworld-set@v0.6.0 helloworld
Output
fetching package /package-examples/helloworld-set from https://github.com/GoogleContainerTools/kpt to helloworld
List the setters
The helloworld-set package contains setters which can be used to
set configuration values from the commandline.
List Command
kpt cfg list-setters helloworld/
Print the list of setters included in the package.
List Output
NAME VALUE SET BY DESCRIPTION COUNT
http-port 80 package-default helloworld port 3
image-tag v0.1.0 package-default helloworld image tag 1
replicas 5 package-default helloworld replicas 1
The package contains 3 setters which may be used to modify the configuration
using kpt set.
Set a field
Setters modify the resource configuration in place by reading the resources, changing values, and writing them back.
Package contents
# helloworld/deploy.yaml
kind: Deployment
metadata:
name: helloworld-gke
...
spec:
replicas: 5 # {"$kpt-set":"replicas"}
Set Command
kpt cfg set helloworld/ replicas 3
Change the replicas value in the configuration from 5 to 3.
Set Output
set 1 fields
Updated package contents
kind: Deployment
metadata:
name: helloworld-gke
...
spec:
replicas: 3 # {"$kpt-set":"replicas"}
...