"Serverless" refers to an architecture in which the infrastructure of your applications is managed by cloud providers. Contrary to its name, a serverless application does require a server but it doesn't require you to run and manage it on your own. Instead, you subscribe to a given cloud provider, such as AWS, Azure or GCP, and pay a subscription fee only for the resources you actually use. Since the resource allocation can be dynamic and depends on your current needs, the serverless model is particularly cost-effective when you want to implement a certain logic that is triggered on demand. Simply, you get your things done and don't pay for the infrastructure that sits idle.

Similarly to cloud providers, Kyma offers a service (known as "functions-as-a-service" or "FaaS") that provides a platform on which you can build, run, and manage serverless applications in Kubernetes. These applications are called Functions and are based on the Function CR objects. They are simple code snippets that implement the exact business logic you define in them. After you create a Function, you can:

• Configure it to be triggered by events coming from external sources to which you subscribe.
• Expose it to an external endpoint (HTTPS).

CAUTION: In its default configuration, Serverless uses persistent volumes as the internal registry to store Docker images for Functions. The default storage size of a single volume is 20 GB. This internal registry is suitable for local development. For production purposes, we recommend to use an external Docker registry.

Serverless relies heavily on Kubernetes resources. It uses Deployments, Services and HorizontalPodAutoscalers to deploy and manage Functions, and Kubernetes Jobs to create Docker images. See how these and other resources process a Function within a Kyma cluster:

CAUTION: Serverless imposes some requirements on the setup of Namespaces. If you create a new Namespace, do not disable sidecar injection in it as Serverless requires Istio for other resources to communicate with Functions correctly. Also, if you apply custom LimitRanges for a new Namespace, they must be higher than or equal to the limits for building Jobs' resources.

1. Create a Function either through the UI or by applying a Function custom resource (CR). This CR contains the Function definition (business logic that you want to execute) and information on the environment on which it should run.

2. Before the Function can be saved or modified, it is first updated and then verified by the defaulting and validation webhooks respectively.

3. Function Controller (FC) detects the new, validated Function CR.

4. FC creates a ConfigMap with the Function definition.

5. Based on the ConfigMap, FC creates a Kubernetes Job that triggers the creation of a Function image.

6. The Job creates a Pod which builds the production Docker image based on the Function's definition. The Job then pushes this image to a Docker registry.

7. FC monitors the Job status. When the image creation finishes successfully, FC creates a Deployment that uses the newly built image.

8. FC creates a Service that points to the Deployment.

9. FC creates a HorizontalPodAutoscaler that automatically scales the number of Pods in the Deployment based on the observed CPU utilization.

10. FC waits for the Deployment to become ready.

Functions support multiple languages through the use of runtimes. To use a chosen runtime, add its name and version as a value in the spec.runtime field of the Function custom resource (CR). If this value is not specified, it defaults to nodejs12. Dependencies for a Node.js Function should be specified using the package.json file format. Dependencies for a Python Function should follow the format used by pip.

See sample Functions for all available runtimes:

In its default configuration, Serverless uses persistent volumes as the internal registry to store Docker images for Functions. The default storage size of a single volume is 20 GB. This internal registry is suitable for local development.

If you use Serverless for production purposes, it is recommended that you use an external registry, such as Docker Hub, Google Container Registry (GCR), or Azure Container Registry (ACR).

Serverless supports two ways of connecting to an external registry:

• You can set up an external registry before installation.

  In this scenario, you can use Kyma overrides to change the default values supplied by the installation mechanism.

• You can switch to an external registry in the runtime.

  In this scenario, you can change the registry on the fly, with Kyma already installed on your cluster. This option gives you way more flexibility and control over the choice of an external registry for your Functions.

Switching registries in the runtime

When you install Kyma with the default internal registry, Helm creates the serverless-registry-config-default Secret in the kyma-system Namespace. This Secret contains credentials used by Kubernetes to pull deployed Functions' images from the internal registry. These credentials also allow Kaniko to push any images to the registry each time a Function is created or updated.

NOTE: If you install Serverless with overrides, you disable the internal registry and specify an external one to use. The serverless-registry-config-default Secret will then contain credentials to the specified external registry instead of the internal one.

Once you have Serverless up and running, you can switch to an external registry:

• Per Namespace, and have even multiple external registries in a cluster, but no more than one per Namespace.
• Cluster-wide, with this configuration overwriting by default the Namespace-scoped one.

Namespace-scoped external registry

To switch to an external registry in a given Namespace, create a Secret CR that:

• Is named serverless-registry-config.
• Is of type kubernetes.io/dockerconfigjson.
• Has the serverless.kyma-project.io/remote-registry: config label.
• Contains these keys with valid values pointing to the external registry:
  • username
  • password
  • serverAddress
  • registryAddress

See this example:

apiVersion: v1
kind: Secret
type: kubernetes.io/dockerconfigjson
metadata:
 name: serverless-registry-config
 namespace: default
 labels:
   serverless.kyma-project.io/remote-registry: config
data:
 username: {VALUE}
 password: {VALUE}
 serverAddress: {VALUE}
 registryAddress: {VALUE}

CAUTION: If you have your own Secret CR in a Namespace and you don't want the system to override it with any cluster-wide configuration, add the serverless.kyma-project.io/managed-by: user label to that Secret CR.

Cluster-wide external registry

To switch to one external registry in the whole cluster, you must create a Secret CR in the kyma-system Namespace. The Secret CR must meet the same requirements as in the case of the Namespace-scoped setup, but you must also add the serverless.kyma-project.io/config: credentials label. This label ensures the Secret CR gets propagated to all Namespaces. Such a cluster-wide configuration will take precedence over a Namespace-scoped one unless the Namespace-scoped configuration blocks it with the serverless.kyma-project.io/managed-by: user label.

CAUTION: Do not remove the serverless.kyma-project.io/config: credentials label from the existing Secret CR in the kyma-system Namespace. If you do so, you will not be able to remove the Secret CR afterwards.

How this works

This implementation has a fallback mechanism that works as follows:

1. Every 5 minutes, Function Controller checks if there is the serverless-registry-config Secret CR in the Namespace with your Function specifying alternative registry to push the Function's image to.
2. If it doesn't find such a Secret CR, Function Controller uses the credentials to the default registry specified in the serverless-registry-config-default Secret CR.

This mechanism also leaves room for a lot of flexibility as you can easily switch between external registries or move back to the internal one. If you remove the serverless-registry-config Secret CR or update it with credentials to a different external registry, you don't lose any images. Function Controller detects any changes in the Secret CR and the images are rebuilt automatically, using cache and delta updates. If you modify the username and password to the registry, the admission webhook automatically encodes these credentials to base64 and sets them as a value under the .dockerconfigjson entry in the Secret CR. These credentials later serve Kubernetes to pull images of deployed Function from the registry, and allow Kaniko to push any newly built or rebuilt images to this registry.

Serverless in Kyma allows you to choose where you want to keep your Function's source code and dependencies. You can either place them directly in the Function custom resource (CR) under the spec.source and spec.deps fields as an inline Function, or store the code and dependencies in a public or private Git repository. Choosing the second option ensures your Function is versioned and gives you more development freedom in the choice of a project structure or an IDE.

Depending on a runtime you use to build your Function (Node.js 12, Node.js 10, or Python 3.8), your Git repository must contain at least a directory with these files:

• handler.js or handler.py with Function's code
• package.json or requirements.txt with Function's dependencies

The Function CR must contain type: git to specify that you use a Git repository for the Function's sources.

To create a Function with the Git source, you must:

1. Create a GitRepository CR with details of your Git repository.
2. Create a Secret (optional, only if you must authenticate to the repository).
3. Create a Function CR with your Function definition and references to the Git repository.

NOTE: For detailed steps, see the tutorial on creating a Function from Git repository sources.

You can have various setups for your Function's Git source with different:

• Directory structures

  You can specify the location of your code dependencies with the baseDir parameter in the Function CR. For example, use "/" if you keep the source files at the root of your repository.

• Authentication methods

  You can define with the spec.auth parameter in the GitRepository CR that you must authenticate to the repository with a password or token (basic), or an SSH key (key).

• Function's rebuild triggers

  You can use the reference parameter in the GitRepository CR to define whether the Function Controller must monitor a given branch or commit in the Git repository to rebuild the Function upon their changes.

A newly created or modified Function CR is first updated by the defaulting webhook and then verified by the validation webhook before the Function Controller starts to process it.

Defaulting webhook

NOTE: It only applies to the Function custom resource (CR).

The defaulting webhook:

• Sets default values for CPU and memory requests and limits for a Function.
• Sets default values for CPU and memory requests and limits for a Kubernetes Job responsible for building the Function's image.
• Adds the maximum and the minimum number of replicas, if not specified already in the Function CR.

• Sets the default runtime nodejs12 unless specified otherwise.

  Parameter	Default value
  resources.requests.cpu	50m
  resources.requests.memory	64Mi
  resources.limits.cpu	100m
  resources.limits.memory	128Mi
  buildResources.requests.cpu	700m
  buildResources.requests.memory	700Mi
  buildResources.limits.cpu	1100m
  buildResources.limits.memory	1100Mi
  minReplicas	1
  maxReplicas	1
  runtime	nodejs12

NOTE: Function's resources and replicas as well as resources for a Kubernetes Job are based on presets. Read about all available presets to find out more.

Validation webhook

It checks the following conditions for these CRs:

1. Function CR

   • Minimum values requested for a Function (CPU, memory, and replicas) and a Kubernetes Job (CPU and memory) responsible for building the Function's image must not be lower than the required ones:

   Parameter	Required value
   minReplicas	1
   resources.requests.cpu	10m
   resources.requests.memory	16Mi
   buildResources.requests.cpu	200m
   buildResources.requests.memory	200Mi

   • Requests are lower than or equal to limits, and the minimum number of replicas is lower than or equal to the maximum one.
   • The Function CR contains all the required parameters.
   • If you decide to set a Git repository as the source of your Function's code and dependencies (spec.type set to git), the spec.reference and spec.baseDir fields must contain values.
   • The format of deps, envs, labels, and the Function name (RFC 1035) is correct.
   • The Function CR contains any envs reserved for the Deployment: FUNC_RUNTIME, FUNC_HANDLER, FUNC_PORT, MOD_NAME, NODE_PATH, PYTHONPATH.

2. GitRepository CR

   • The spec.url parameter must:

     • Not be empty
     • Start with the http(s), git, or ssh prefix
     • End with the .git suffix

   • If you use SSH to authenticate to the repository:

     • spec.auth.type must be set to key
     • spec.auth.secretName must not be empty

   • If you use HTTP(S) to point to the repository that requires authentication (spec.auth):

     • spec.auth.type must be set to either key (SSH key) or basic (password or token)
     • spec.auth.secretName must not be empty

Admission webhook

There is also the admission webhook that is only triggered in the scenario when you switch in the runtime from one registry to another.

To switch registries in the runtime, you must create or update a Secret CR that complies with specific requirements. This Secret CR, among other details, contains a username and password to the registry. The admission webhook encodes these credentials to base64, a format that is required by Kaniko - the Function's job building tool - to access the registry and push a Function's image to it. These encoded credentials also allow Kubernetes to pull images of deployed Functions from the registry. The admission webhook adds these credentials to the created Secret CR. They take the form of the .dockerconfigjson entry with a valid value. The admission webhook also updates this entry's value each time the username and password change.

Requirements

This admission webhook is triggered every time you CREATE or UPDATE a Secret in any Namespace, as long as the Secret contains the serverless.kyma-project.io/remote-registry: config label.

Function's resources and replicas as well as resources for image-building Jobs are based on presets. A preset is a predefined group of values. There are three groups of presets defined for a Function CR and include the presents for:

• Function's resources
• Function's replicas
• Image-building Job's resources

Configuration

To add a new preset to the Serverless configuration for the defaulting webhook to set it on all Function CRs, update the values.yaml file in the Serverless chart. To do it, change the configuration for the webhook.values.function.replicas.presets, webhook.values.function.resources.presets or webhook.values.buildJob.resources.presets parameters. Read the Serverless chart configuration to find out more.

Usage

If you want to apply values from a preset to a single Function, override the existing values for a given preset in the Function CR. To do it, first remove the relevant fields from the Function CR and then add the relevant preset labels. For example, to modify the default values for buildResources, remove all its entries from the Function CR and add an appropriate serverless.kyma-project.io/build-resources-preset: {PRESET} label to the Function CR.

Function's replicas

To apply values ​​from a given preset, use the serverless.kyma-project.io/replicas-preset: {PRESET} label in the Function CR.

Function's resources

To apply values ​​from a given preset, use the serverless.kyma-project.io/function-resources-preset: {PRESET} label in the Function CR.

Build Job's resources

To apply values ​​from a given preset, use the serverless.kyma-project.io/build-resources-preset: {PRESET} label in the Function CR.

To access a Function within the cluster, use the {function-name}.{namespace}.svc.cluster.local endpoint, such as test-function.default.svc.cluster.local. To expose a Function outside the cluster, you must create an APIRule custom resource (CR):

1. Create the APIRule CR where you specify the Function to expose, define an Oathkeeper Access Rule to secure it, and list which HTTP request methods you want to enable for it.

2. The API Gateway Controller detects a new APIRule CR and reads its definition.

3. The API Gateway Controller creates an Istio Virtual Service and Access Rules according to details specified in the CR. Such a Function service is available under the {host-name}.{domain} endpoint, such as my-function.kyma.local.

This way you can specify multiple API Rules with different authentication methods for a single Function service.

TIP: See the tutorial for a detailed example.

NOTE: If you are using Minikube, before you can access the function you must add the endpoint to the Minikube IP entry in the /etc/hosts file.

From the moment you create a Function (Function CR) until the time it is ready, it goes through three processing stages that are defined as these condition types:

1. ConfigurationReady (PrinterColumn CONFIGURED)
2. BuildReady (PrinterColumn BUILT)
3. Running (PrinterColumn RUNNING)

For a Function to be considered ready, the status of all three conditions must be True:

NAME            CONFIGURED   BUILT     RUNNING   RUNTIME    VERSION   AGE
test-function   True         True      True      nodejs12   1         96s

When you update an existing Function, conditions change asynchronously depending on the change type.

The diagrams illustrate all three core status changes in the Function processing circle that the Function Controller handles. They also list all custom resources involved in this process and specify in which cases their update is required.

NOTE: Before you start reading, see the Function CR document for the custom resource detailed definition, the list of all Function's condition types and reasons for their success or failure.

Configured

This initial phase starts when you create a Function CR with configuration specifying the Function's setup. It ends with creating a ConfigMap that is used as a building block for a Function image.

Built

This phase involves creating and processing the Job CR. It ends successfully when the Function image is built and sent to the Docker registry. If the image already exists and only an update is required, the Docker image receives a new tag.

Updating an existing Function requires an image rebuild only if you change the Function's body (source) or dependencies (deps). An update of Function's other configuration details, such as environment variables, replicas, resources, or labels, does not require image rebuild as it only affects the Deployment.

NOTE: Each time you update Function's configuration, the Function Controller deletes all previous Job CRs for the given Function's UID.

Running

This stage revolves around creating a Deployment, Service and HorizontalPodAutoscaler or updating them when configuration changes were made in the Function CR or the Function image was rebuilt.

In general, the Deployment is considered updated when both configuration and the image tag in the Deployment are up to date. Service and HorizontalPodAutoscaler are considered updated when there are proper labels set and configuration is up to date.

Thanks to the implemented reconciliation loop, the Function Controller constantly observes all newly created or updated resources. If it detects changes, it fetches the appropriate resource's status and only then updates the Function's status.

To eliminate potential security risks when using Functions, bear in mind these few facts:

• Kyma does not run any security scans against Functions and their images. Before you store any sensitive data in Functions, consider the potential risk of data leakage.

• By default, JSON Web Tokens (JWTs) issued by Dex do not provide the scope parameter for Functions. This means that if you expose your Function and secure it with a JWT, you can use the token to validate access to all Functions within the cluster.

• Kyma does not define any authorization policies that would restrict Functions' access to other resources within the Namespace. If you deploy a Function in a given Namespace, it can freely access all events and APIs of services within this Namespace.

• All administrators and regular users who have access to a specific Namespace in a cluster can also access:

  • Source code of all Functions within this Namespace
  • Internal Docker registry that contains Function images
  • Secrets allowing the build Job to pull and push images from and to the Docker registry (in non-system Namespaces)

Serverless Functions are adapted to run in a non-privileged mode. If you enable Pod Security Policies in your cluster, Functions will have the following security measures set in place:

• The root filesystem is set to read-only mode, apart from the /tmp directory which is read-write.
• The Function's container is non-privileged and runs as a non-root user.
• All Linux capabilities are dropped.

To configure the Serverless chart, override the default values of its values.yaml file. This document describes parameters that you can configure.

TIP: To learn more about how to use overrides in Kyma, see the following documents:

• Helm overrides for Kyma installation
• Top-level charts overrides

Configurable parameters

This table lists the configurable parameters, their descriptions, and default values for both cluster and local installations.

NOTE: Limited memory and CPU resources on Minikube directly affect the Serverless functionality as you can process only a limited number of Functions at the same time. Also, their processing time is significantly longer. To process large workloads, we recommend using the cluster setup.

TIP: To learn more, read the official documentation on resource units in Kubernetes.

The gitrepositories.serverless.kyma-project.io CustomResourceDefinition (CRD) is a detailed description of the kind of data and the format used to define and manage Git repositories that store the Function's source code and dependencies. To get the up-to-date CRD and show the output in the YAML format, run this command:

kubectl get crd gitrepositories.serverless.kyma-project.io -o yaml

Sample custom resource

This is a sample custom resource that creates a GitRepository object pointing to a Git repository with the Function's source code and dependencies. This resource specifies that the repository requires an SSH key to authenticate to it and points to the Secret that stores these credentials.

apiVersion: serverless.kyma-project.io/v1alpha1
kind: GitRepository
metadata:
  name: sample-with-auth
spec:
  url: "git@github.com:sample-organization/sample-repo.git"
  auth:
    type: key
    secretName: kyma-git-creds

Custom resource parameters

This table lists all the possible parameters of a given resource together with their descriptions:

Related resources and components

These are the resources related to this CR:

These components use this CR:

This tutorial shows how you can expose your Function to access it outside the cluster, through an HTTP proxy. To expose it, use an APIRule custom resource (CR) managed by the in-house API Gateway Controller. This controller reacts to an instance of the APIRule CR and, based on its details, it creates an Istio Virtual Service and Oathkeeper Access Rules that specify your permissions for the exposed Function.

When you complete this tutorial, you get a Function that:

• Is available on an unsecured endpoint (handler set to noop in the APIRule CR).
• Accepts the GET, POST, PUT, and DELETE methods.

NOTE: To learn more about securing your Function, see the tutorial.

Prerequisites

This tutorial is based on an existing Function. To create one, follow the Create a Function tutorial.

Steps

Follows these steps:

This tutorial shows how you can bind a sample instance of the Redis service to a Function. After completing all steps, you will get the Function with encoded Secrets to the service. You can use them for authentication when you connect to the service to implement custom business logic of your Function.

To create the binding, you will use ServiceBinding and ServiceBindingUsage custom resources (CRs) managed by the Service Catalog.

NOTE: See the document on provisioning and binding to learn more about binding ServiceInstances to applications in Kyma.

Prerequisites

This tutorial is based on an existing Function. To create one, follow the Create a Function tutorial.

Steps

Follows these steps:

Test the Function

To test if the Secret has been properly connected to the Function:

1. Change the Function's code to:​

   Click to copy

   module.exports = {
     main: function (event, context) {
       return "Redis port: " + process.env.REDIS_PORT;
     },
   };

2. Expose the Function through an API Rule, and access the Function's external address. You should get this result:

   Click to copy

   Redis port: 6379

This tutorial shows how to trigger a Function with an event from an Application connected to Kyma.

NOTE: To learn more about events flow in Kyma, read the eventing documentation.

Prerequisites

This tutorial is based on an existing Function. To create one, follow the Create a Function tutorial.

You must also have:

• An Application bound to a specific Namespace. Read the tutorials to learn how to create an Application and bind it to a Namespace.
• An event service (an API of AsyncAPI type) registered in the desired Application. Read the tutorial to learn how to do it.
• A Service Instance created for the registered service to expose events in a specific Namespace. Read the tutorial for details.

Steps

Follows these steps:

Test the trigger

CAUTION: Before you follow steps in this section and send a sample event, bear in mind that it will be propagated to all services subscribed to this event type.

To test if the Trigger CR is properly connected to the Function:

1. Change the Function's code to:​

   Click to copy

   module.exports = {
     main: function (event, context) {
       console.log("User created: ", event.data);
     }
   }

2. Send an event manually to trigger the function. The first example shows the implementation introduced with the Kyma 1.11 release where a CloudEvent is sent directly to the Event Mesh. In the second example, an event also reaches the Event Mesh, but it is first modified by the compatibility layer to the format compliant with the CloudEvents specification. This solution ensures compatibility if your events follow a format other than CloudEvents, or you use the Event Bus available before 1.11.

   TIP: For details on CloudEvents, exposed endpoints, and the compatibility layer, read about event processing and delivery.

   • Send CloudEvents directly to Event Mesh
   • Send events to Event Mesh through compatibility layer

   • CLUSTER_DOMAIN is the domain of your cluster, such as kyma.local.

   • CERT_FILE_NAME and KEY_FILE_NAME are client certificates for a given Application. You can get them by completing steps in the tutorial.

3. After sending an event, you should get this result from logs of your Function's latest Pod:

   Click to copy

   User created: 123456789

This tutorial shows how you can build a Function from code and dependencies stored in a Git repository, which is an alternative way to keeping the code in the Function CR. The tutorial is based on the Function from the orders service example. It describes steps required to fetch Function's source code and dependencies from a public Git repository that does not require any authentication method. However, it also provides additional guidance on how to secure it if you are using a private repository.

NOTE: This tutorial shows an alternative way of storing Function's code and dependencies. If you want to follow the whole end-to-end flow described for Functions in the Serverless tutorials, create an inline Function instead. To learn more about Git repository sources for Functions and different ways of securing your repository, read about the Git source type.

Steps

Follows these steps:

By default, you install Kyma with Serverless that uses the internal Docker registry running on a cluster. This tutorial shows how to switch to an external Docker registry from one of these cloud providers using an override:

• Docker Hub
• Google Container Registry (GCR)
• Azure Container Registry (ACR)

CAUTION: Function images are not cached in the Docker Hub. The reason is that this registry is not compatible with the caching logic defined in Kaniko that Serverless uses for building images.

Prerequisites

Steps

Create required cloud resources

Override Serverless configuration

Apply the following Secret with an override to a cluster or Minikube. Run:

CAUTION: If you want to set an external Docker registry before you install Kyma, manually apply the Secret to the cluster before you run the installation script.

Trigger installation

Trigger Kyma installation or update it by labeling the Installation custom resource. Run:

kubectl -n default label installation/kyma-installation action=install

This tutorial shows how you can switch to an external Docker registry in a specific Namespace, with Serverless already installed on your cluster. This example relies on the default Namespace but you can use any other. You will create a Secret custom resource (CR) with credentials to one of these registries:

• Docker Hub
• Google Container Registry (GCR)
• Azure Container Registry (ACR)

After this change, any Function deployed in the default Namespace will store images in this registry.

CAUTION: Function images are not cached in the Docker Hub. The reason is that this registry is not compatible with the caching logic defined in Kaniko that Serverless uses for building images.

Prerequisites

Steps

Create required cloud resources

To create cloud resources required for a given registry provider, follow the steps described in the Set an external Docker registry tutorial.

Create a Secret CR

Create a Secret CR in the default Namespace. Such a Secret must contain the serverless.kyma-project.io/remote-registry: config label and the required data (username, password, serverAddress, and registryAddress):

cat <<EOF | kubectl apply -f -
apiVersion: v1
kind: Secret
type: kubernetes.io/dockerconfigjson
metadata:
 name: serverless-registry-config
 namespace: default
 labels:
   serverless.kyma-project.io/remote-registry: config
data:
 username: {VALUE}
 password: {VALUE}
 serverAddress: {VALUE}
 registryAddress: {VALUE}
EOF

CAUTION: If you want to create a cluster-wide Secret, you must create it in the kyma-system Namespace and add the serverless.kyma-project.io/config: credentials label. Read more about requirements for Secret CRs.

Test the registry switch

Create a Function in the default Namespace and check if the Function's Deployment points to the external registry using this command:

kubectl get pods -n default -l serverless.kyma-project.io/resource=deployment -o jsonpath='{ ...image }'

This tutorial shows how you can automate the deployment of local Kyma resources on a cluster using the GitOps logic. You will use Kyma CLI to create an inline Python Function with a trigger. You will later push both resources to a GitHub repository of your choice and set up a GitOps operator to monitor the given repository folder and synchronize any changes in it with your cluster. For the purpose of this tutorial, you will install and use the Flux GitOps operator and a lightweight k3d cluster.

TIP: Although this tutorial uses Flux to synchronize Git resources with the cluster, you can use an alternative GitOps operator for this purpose, such as Argo.

Prerequisites

All you need before you start is to have the following:

• Docker
• Git repository
• Homebrew
• Kyma CLI

Steps

These sections will lead you through the whole installation, configuration, and synchronization process. You will first install k3d and create a cluster for your custom resources (CRs). Then, you will need to apply the necessary Custom Resource Definitions (CRDs) from Kyma to be able to create Functions and triggers. Finally, you will install Flux and authorize it with the write access to your GitHub repository in which you store the resource files. Flux will automatically synchronize any new changes pushed to your repository with your k3d cluster.

Install and configure a k3d cluster

1. Install k3d using Homebrew on macOS:

   Click to copy

   brew install k3d

2. Create a default k3d cluster with a single server node:

   Click to copy

   k3d cluster create {CLUSTER_NAME}

   This command also sets your context to the newly created cluster. Run this command to display the cluster information:

   Click to copy

   kubectl cluster-info

3. Apply the functions.serverless.kyma-project.io and triggers.eventing.knative.dev CRDs from sources in the kyma repository. You will need them to create the Function and Trigger CRs on the cluster.

   Click to copy

   kubectl apply -f https://raw.githubusercontent.com/kyma-project/kyma/master/resources/cluster-essentials/files/functions.serverless.crd.yaml && kubectl apply -f https://raw.githubusercontent.com/kyma-project/kyma/master/resources/cluster-essentials/files/triggers.eventing.knative.dev.crd.yaml

4. Run this command to make sure the CRs are applied:

   Click to copy

   kubectl get customresourcedefinitions

Prepare your local workspace

1. Create a workspace folder in which you will create source files for your Function:

   Click to copy

   mkdir {WORKSPACE_FOLDER}

2. Use the init Kyma CLI command to create a local workspace with default configuration for a Python Function:

   Click to copy

   kyma init function --runtime python38 --dir $PWD/{WORKSPACE_FOLDER}

   TIP: Python 3.8 is only one of the available runtimes. Read about all supported runtimes and sample Functions to run on them.

   This command will download the following files to your workspace folder:

• config.yaml with the Function's configuration
• 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

  It will also set sourcePath in the config.yaml file to the full path of the workspace folder:

  Click to copy

  name: my-function
  namespace: default
  runtime: python38
  source:
      sourceType: inline
      sourcePath: {FULL_PATH_TO_WORKSPACE_FOLDER}

Install and configure Flux

You can now install the Flux operator, connect it with a specific Git repository folder, and authorize Flux to automatically pull changes from this repository folder and apply them on your cluster.

1. Install Flux:

   Click to copy

   brew install fluxctl

2. Create a flux Namespace for the Flux operator's CRDs:

   Click to copy

   kubectl create namespace flux

3. Export details of your GitHub repository - its name, the account name, and related e-mail address. You must also specify the name of the folder in your GitHub repository to which you will push Function and Trigger CRs built from local sources. If you don't have this folder in your repository yet, you will create it in further steps. Flux will synchronize the cluster with the content of this folder on the main (master) branch.

   Click to copy

   export GH_USER="{USERNAME}"
   export GH_REPO="{REPOSITORY_NAME}"
   export GH_EMAIL="{EMAIL_OF_YOUR_GH_ACCOUNT}"
   export GH_FOLDER="{GIT_REPO_FOLDER_FOR_FUNCTION_RESOURCES}"

4. Run this command to apply CRDs of the Flux operator to the flux Namespace on your cluster:

   Click to copy

   fluxctl install \
   --git-user=${GH_USER} \
   --git-email=${GH_EMAIL} \
   --git-url=git@github.com:${GH_USER}/${GH_REPO}.git \
   --git-path=${GH_FOLDER} \
   --namespace=flux | kubectl apply -f -

   You will see that Flux created these CRDs:

   Click to copy

   serviceaccount/flux created
   clusterrole.rbac.authorization.k8s.io/flux created
   clusterrolebinding.rbac.authorization.k8s.io/flux created
   deployment.apps/flux created
   secret/flux-git-deploy created
   deployment.apps/memcached created
   service/memcached created

5. List all Pods in the flux Namespace to make sure that the one for Flux is in the Running state:

   Click to copy

   kubectl get pods --namespace flux

   Expect a response similar to this one:

   Click to copy

   NAME                        READY   STATUS    RESTARTS   AGE
   flux-75758595b9-m4885       1/1     Running   0          32m

6. Obtain the certificate (SSH key) that Flux generated:

   Click to copy

   fluxctl identity --k8s-fwd-ns flux

7. Run this command to copy the SSH key to the clipboard:

   Click to copy

   fluxctl identity --k8s-fwd-ns flux | pbcopy

8. Go to Settings in your GitHub account:

   

9. Go to the SSH and GPG keys section and select the New SSH key button:

   

10. Provide the new key name, paste the previously copied SSH key, and confirm changes by selecting the Add SSH Key button:

    

Create a Function

Now that Flux is authenticated to pull changes from your Git repository, you can start creating CRs from your local workspace files. You will create a sample inline Function and modify it by adding a trigger to it.

1. Back in the terminal, clone this GitHub repository to your current workspace location:

   Click to copy

   git clone git@github.com:${GH_USER}/${GH_REPO}.git

2. Go to the repository folder:

   Click to copy

   cd ${GH_REPO}

3. If the folder you specified during the Flux configuration does not exist yet in the Git repository, create it:

   Click to copy

   mkdir ${GH_FOLDER}

4. Run the apply Kyma CLI command to create a Function CR in the YAML format in your remote GitHub repository. This command will generate the output in the my-function.yaml file.

   Click to copy

   kyma apply function --filename {FULL_PATH_TO_LOCAL_WORKSPACE_FOLDER}/config.yaml --output yaml --dry-run > ./${GH_FOLDER}/my-function.yaml

5. Push the local changes to the remote repository:

   Click to copy

   git add .                        # Stage changes for the commit
   git commit -m 'Add my-function'  # Add a commit message
   git push origin main             # Push changes to the "main" branch of your Git repository. If you have a repository with the "master" branch, use this command instead: git push origin master

6. Go to the GitHub repository to check that the changes were pushed.

7. By default, Flux pulls CRs from the Git repository and pushes them to the cluster in 5-minute intervals. To enforce immediate synchronization, run this command from the terminal:

   Click to copy

   fluxctl sync --k8s-fwd-ns flux

8. Make sure that the Function CR was applied by Flux to the cluster:

   Click to copy

   kubectl get functions

Create a Trigger

1. From your workspace folder, modify the local config.yaml file by adding trigger details (triggers) to your Function as follows:

   Click to copy

   name: my-function
   namespace: default
   runtime: python38
   source:
       sourceType: inline
       sourcePath: {FULL_PATH_TO_WORKSPACE_FOLDER}
   triggers:
     - version: evt1
       source: the-source
       type: t1

2. Create the Function resource from local sources and place the output in your Git repository folder:

   Click to copy

   kyma apply function --filename {FULL_PATH_TO_LOCAL_WORKSPACE_FOLDER}/config.yaml --output yaml --dry-run > ./{GH_REPO}/${GH_FOLDER}/my-function.yaml

3. Push the local changes to the remote repository:

   Click to copy

   git add .
   git commit -m 'Update my-function'
   git push origin main                # Or run: git push origin master

4. Go to the GitHub repository and see that the my-function.yaml file was modified as intended.

5. From the terminal, force Flux to immediately propagate the Git repository changes to the cluster:

   Click to copy

   fluxctl sync --k8s-fwd-ns flux

6. Check that the new Trigger CR for the Function was created:

   Click to copy

   kubectl get triggers

You can see that Flux synchronized the resources and the new Trigger CR for the Function was added to your cluster.

Reverting feature

Once you set it up, Flux will keep monitoring the given Git repository folder for any changes. If you modify the existing resources directly on the cluster, Flux will automatically revert these changes and update the given resource back to its version on the main (master) branch of the Git repository.