Generic Webhook Receiver

The generic webhook receiver responds to any inbound POST request by determining whether it meets user-defined criteria, then executing user-defined actions on a user-defined set of resources when it does.

note

Currently, these actions are limited to "refreshing" Warehouse resources, which triggers their artifact discovery processes, so a typical use of this component is responding to "push" events from artifact repositories that lack dedicated webhook receiver implementations. Since this component effectively enables imperatively refreshing a Warehouse from any external process, other uses are possible and practical.

Configuring the Receiver

Base Configuration

A Generic webhook receiver must reference a Kubernetes Secret resource with a secret key in its data map.

info

Kargo incorporates the secret into the generation of a hard-to-guess URL for the receiver. This URL serves as a de facto shared secret and authentication mechanism.

note

The following commands are suggested for generating and base64-encoding a complex secret:

secret=$(openssl rand -base64 48 | tr -d '=+/' | head -c 32)
echo "Secret: $secret"
echo "Encoded secret: $(echo -n $secret | base64)"

apiVersion: v1
kind: Secret
metadata:
  name: wh-secret
  namespace: kargo-demo
  labels:
    kargo.akuity.io/cred-type: generic
data:
  secret: <base64-encoded secret>
---
apiVersion: kargo.akuity.io/v1alpha1
kind: ProjectConfig
metadata:
  name: kargo-demo
  namespace: kargo-demo
spec:
  webhookReceivers:
    - name: my-receiver
      generic:
        secretRef:
          name: wh-secret

Defining Actions

Actions are defined by:

1. actionType
2. whenExpression
3. targetSelectionCriteria

actionType

The actionType field specifies the action that should be performed.

apiVersion: kargo.akuity.io/v1alpha1
kind: ProjectConfig
metadata:
  name: kargo-demo
  namespace: kargo-demo
spec:
  webhookReceivers:
    - name: my-receiver
      generic:
        secretRef:
          name: wh-secret
      actions:
        - actionType: Refresh

note

The only currently supported actionType is Refresh.

whenExpression

Use whenExpression to ensure that an action is only executed when specific criteria are met, providing fine-grained control over webhook behavior.

The following example depicts an action that is executed only when the request contains an X-Event-Type header with the value push:

apiVersion: kargo.akuity.io/v1alpha1
kind: ProjectConfig
metadata:
  name: kargo-demo
  namespace: kargo-demo
spec:
  webhookReceivers:
    - name: my-receiver
      generic:
        secretRef:
          name: wh-secret
      actions:
        - actionType: Refresh
          whenExpression: "request.header("X-Event-Type") == 'push'"

note

This is can be left empty if the action should run unconditionally.

targetSelectionCriteria

targetSelectionCriteria is used to select resources that an action needs to be performed on. There are three ways to define targetSelectionCriteria:

1. By Name
2. By Labels
3. By Values in an Index

All methods support both static and dynamic values.

note

Using more than one of the above selects resources at the logical intersection of the criteria. (i.e. Criteria are "ANDed.")

By Name

The simplest way to select a resource is by specifying its name.

The following example depicts targetSelectionCriteria that selects Warehouse resources by a static name.

apiVersion: kargo.akuity.io/v1alpha1
kind: ProjectConfig
metadata:
  name: kargo-demo
  namespace: kargo-demo
spec:
  webhookReceivers:
    - name: my-receiver
      generic:
        secretRef:
          name: wh-secret
      actions:
        - actionType: Refresh
          whenExpression: "request.header('X-Event-Type') == 'push'"
          targetSelectionCriteria:
            - kind: Warehouse
              name: my-warehouse

The following example depicts targetSelectionCriteria that selects Warehouse resources by a name that is dynamically sourced from a repository URL in the request body.

apiVersion: kargo.akuity.io/v1alpha1
kind: ProjectConfig
metadata:
  name: kargo-demo
  namespace: kargo-demo
spec:
  webhookReceivers:
    - name: my-receiver
      generic:
        secretRef:
          name: wh-secret
      actions:
        - actionType: Refresh
          whenExpression: "request.header('X-Event-Type') == 'push'"
          targetSelectionCriteria:
            - kind: Warehouse
              name: "${{ normalizeGit(request.body.repository.name) }}"

By Labels

The following example depicts targetSelectionCriteria that selects Warehouse resources with an environment label whose value is prod:

apiVersion: kargo.akuity.io/v1alpha1
kind: ProjectConfig
metadata:
  name: kargo-demo
  namespace: kargo-demo
spec:
  webhookReceivers:
    - name: my-receiver
      generic:
        secretRef:
          name: wh-secret
      actions:
        - actionType: Refresh
          whenExpression: "request.header('X-Event-Type') == 'push'"
          targetSelectionCriteria:
            - kind: Warehouse
              labelSelector:
                matchLabels:
                  environment: prod

The following example depicts targetSelectionCriteria that selects Warehouse resources with a service label whose value is either ui or api:

apiVersion: kargo.akuity.io/v1alpha1
kind: ProjectConfig
metadata:
  name: kargo-demo
  namespace: kargo-demo
spec:
  webhookReceivers:
    - name: my-receiver
      generic:
        secretRef:
          name: wh-secret
      actions:
        - actionType: Refresh
          whenExpression: "request.header('X-Event-Type') == 'push'"
          targetSelectionCriteria:
            - kind: Warehouse
              labelSelector:
                matchExpressions:
                  - key: service
                    operator: In
                    values: ["ui", "api"]

By Values in an Index

Use indexSelector to retrieve resources by a cached index.

The following example depicts targetSelectionCriteria that dynamically selects Warehouse resources that contain subscriptions to the normalized git URL from the request body.

actions:
  - actionType: Refresh
    whenExpression: "request.header('X-Event-Type') == 'push'"
    targetSelectionCriteria:
      - kind: Warehouse
        indexSelector:
          matchIndices:
            - key: subscribedURLs
              operator: Equals
              value: "${{ normalizeGit(request.body.repository.url) }}"

note

subscribedURLs is the only available index. It refers to Warehouse resources that contain subscriptions for a provided repository URL.

Expression Reference

The Generic webhook receiver extends built-in expr-lang support with utilities that can be used to help resolve targetSelectionCriteria information from incoming requests. The following reference contains the variables and functions available for yeilding dynamic values.

• request.body
• request.header
• request.headers
• request.params
• normalizeGit
• normalizeImage
• normalizeChart

request.body

request.body is structured data parsed from the original request body which is assumed to contain valid JSON. Fields can be accessed using bracket or dot-notation. For example, data.address.city would access the city property nested within the address object, and data.users[0] would access the first item in a users array.

request.header(headerKey)

Retrieves first value for headerKey.

It has one argument:

• headerKey (Required): Case-insensitive header key.

If headerKey is not present in the request headers, an empty string will be returned.

request.headers(headerKey)

Retrieves all values for headerKey.

It has one argument:

• headerKey (Required): Case-insensitive header key.

If headerKey is not present in the request headers, an empty string array will be returned.

request.params(queryParamKey)

Retrieves the query param value for the provided query param key.

It has one argument:

• queryParamKey (Required): URL query parameter key.

If queryParamKey is not present in the request headers, an empty string will be returned.

normalizeGit(url)

Normalizes Git URLs of the following forms:

• http[s]://[proxy-user:proxy-pass@]host.xz[:port][/path/to/repo[.git][/]]
• ssh://[user@]host.xz[:port][/path/to/repo[.git][/]]
• [user@]host.xz[:path/to/repo[.git][/]]

This is useful for the purposes of comparison and also in cases where a canonical representation of a Git URL is needed. Any URL that cannot be normalized will be returned as-is.

It has one argument:

• url (Required): The URL of a git repository.

The returned value is a string.

normalizeImage(url)

Normalizes image repository URLs. Notably, hostnames docker.io and index.docker.io, if present, are dropped. The optional /library prefix for official images from Docker Hub, if included, is also dropped. Valid, non-Docker Hub repository URLs will be returned unchanged.

This is useful for the purposes of comparison and also in cases where a canonical representation of a repository URL is needed. Any URL that cannot be normalized will be returned as-is.

It has one argument:

• url (Required): The URL of an image repository.

The returned value is a string.

normalizeChart(url)

Normalizes a chart repository URL for purposes of comparison. Crucially, this function removes the oci:// prefix from the URL if there is one.

It has one argument:

• url (Required): The URL of a chart repository.

The returned value is a string.

Retrieving the Receiver's URL

Kargo will generate a hard-to-guess URL from the receiver's configuration. This URL can be obtained using a command such as the following:

kubectl get projectconfigs kargo-demo \
  -n kargo-demo \
  -o=jsonpath='{.status.webhookReceivers}'