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Manage Functions with Kyma CLI

This tutorial shows how to use the available CLI commands to manage Functions in Kyma. You will see how to:

Create local files that contain the basic configuration for a sample "Hello World" Python Function (kyma init function).
Generate a Function custom resource (CR) from these files and apply it on your cluster (kyma apply function).
Fetch the current state of your Function's cluster configuration after it was modified (kyma sync function).

NOTE: Read about Istio sidecars in Kyma and why you want them. Then, check how to enable automatic Istio sidecar proxy injection. For more details, see Default Istio setup in Kyma.

This tutorial is based on a sample Python Function run on a lightweight k3d cluster.

Prerequisites

Before you start, make sure you have these tools installed:

Docker
Kyma CLI
Kyma installed locally or on a cluster

Steps

Follow these steps:

Run the init Kyma CLI command to create local files with the default configuration for a Python Function. Go to the folder in which you want to initiate the workspace content and run this command:
NOTE: Learn why you want sidecar and how to enabled them. Follow Istio sidecars in Kyma and why you want them, Default Istio setup in Kyma and Enable automatic Istio sidecar proxy injection
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```
kyma init function --runtime python39 --name {FUNCTION_NAME}
```
Alternatively, use the --dir {FULL_FOLDER_PATH} flag to point to the directory where you want to create the Function's source files.
NOTE: Python 3.9 is only one of the available runtimes. Read about all supported runtimes and sample Functions to run on them.
The init command creates these files in your workspace folder:

config.yaml with the Function's configuration

NOTE: See the detailed description of all fields available in the config.yaml file.

handler.py with the Function's code and the simple "Hello World" logic
requirements.txt with an empty file for your Function's custom dependencies
This command also sets sourcePath in the config.yaml file to the full path of the workspace folder:
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```
name: my-function
namespace: default
runtime: python39
source:
    sourceType: inline
    sourcePath: {FULL_PATH_TO_WORKSPACE_FOLDER}
```

Run the apply Kyma CLI command to create a Function CR in the YAML format on your cluster:
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```
kyma apply function
```
TIP: To apply a Function from a different location, use the --filename flag followed by the full path to the config.yaml file.
Alternatively, use the --dry-run flag to list the file that will be created before you apply it. You can also preview the file's content in the format of your choice by adding the --output {FILE_FORMAT} flag, such as --output yaml.
Once applied, view the Function's details on the cluster:
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```
kubectl describe function {FUNCTION_NAME}
```

Change the Function's source code on the cluster to return "Hello Serverless!":

a) Edit the Function:

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kubectl edit function {FUNCTION_NAME}

b) Modify source as follows:

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...
spec:
  runtime: python39
  source: |-
    def main(event, context):
        return "Hello Serverless!"

Fetch the content of the resource to synchronize your local workspace sources with the cluster changes:
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```
kyma sync function {FUNCTION_NAME}
```
Check the local handler.py file with the Function's code to make sure that the cluster changes were fetched:
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```
cat handler.py
```
This command returns the result confirming that the local sources were synchronized with cluster changes:
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```
def main(event, context):
    return "Hello Serverless!"
```