TriggerBindings

A TriggerBinding is a resource that specifies the fields in the event payload from which you want to extract data as well as the fields in your corresponding TriggerTemplate to populate with the extracted values. In other words, it binds payload fields to fields in the [TriggerTemplate] and for this to work the fields specified in the [TriggerBinding] And the corresponding [TriggerTemplate] must match. You can then use the populated fields in your [TriggerTemplate] to populate fields in the [TaskRun] or [PipelineRun] associated with that [TriggerTemplate]. Tekton also supports a cluster-scoped version called a ClusterTriggerBinding to encourage reusability across your entire cluster.

Structure of a TriggerBinding

Below is an example TriggerBinding definition:

apiVersion: triggers.tekton.dev/v1beta1
kind: TriggerBinding
metadata:
  name: pipeline-binding
spec:
  params:
  - name: gitrevision
    value: $(body.head_commit.id)
  - name: gitrepositoryurl
    value: $(body.repository.url)
  - name: contenttype
    value: $(header.Content-Type)

TriggerBindings vs. ClusterTriggerBindings

A ClusterTriggerBinding is a cluster-scoped TriggerBinding that you can reuse across your entire cluster. You can reference a ClusterTriggerBinding in any EventListener in any namespace. You can specify multiple ClusterTriggerBindings within your Trigger as well as specify the same ClusterTriggerBinding in multiple Triggers.

Below is an example ClusterTriggerBinding definition:

apiVersion: triggers.tekton.dev/v1beta1
kind: ClusterTriggerBinding
metadata:
  name: pipeline-clusterbinding
spec:
  params:
    - name: gitrevision
      value: $(body.head_commit.id)
    - name: gitrepositoryurl
      value: $(body.repository.url)
    - name: contenttype
      value: $(header.Content-Type)

When referencing a ClusterTriggerBinding, you must specify a kind value within the bindings field. The default is TriggerBinding which denotes a namespaced TriggerBinding. For example:

---
apiVersion: triggers.tekton.dev/v1beta1
kind: EventListener
metadata:
  name: listener-clustertriggerbinding
spec:
  serviceAccountName: tekton-triggers-example-sa
  triggers:
    - name: foo-trig
      bindings:
        - ref: pipeline-clusterbinding
          kind: ClusterTriggerBinding
        - ref: message-clusterbinding
          kind: ClusterTriggerBinding
      template:
        ref: pipeline-template

Specifying paramters

A TriggerBinding allows you to specify parameters (params) that Tekton passes to the corresponding TriggerTemplate. For each parameter, you must specify a name and a value field with the appropriate values.

Accessing data in HTTP JSON payloads

Tekton can use a TriggerBinding to access data in the headers and body of an HTTP JSON payload. To do so, it uses JSONPath expressions encapsulated within a $() wrapper. Keys in HTTP JSON headers are case-sensitive.

For example, below is a valid expression:

$(body.key1)
$(.body.key)

On the other hand, the expressions below are invalid:

.body.key1 # INVALID - Expression is not wrapped in `$()`.
$({body) # INVALID - Trailing curly brace is missing.

If a $() wrapper is embedded inside another $() wrapper, Tekton parses the contents of the innermost wrapper as the JSONPath expression. For example:

$($(body.b)) # Parsed as $(body.b)
$($($(body.b))) # Parsed as $(body.b)

Accessing JSON keys containing periods (.)

To access a JSON key that contains a period (.), you must escape the period with a backslash (\.). For example:

# Body contains a `tekton.dev` field: {"body": {"tekton.dev": "triggers"}}
$(body.tekton\.dev) -> "triggers"

Fallback to default values

If Tekton fails to resolve the JSONPath expressions you have configured against the HTTP JSON payload, it falls back to the default value in the corresponding TriggerTemplate, if specified.

Field binding examples

Below are some examples of Tekton performing field binding based on the most commonly used field definitions:

`$(body)` -> replaced by the entire body

$(body) -> "{"key1": "value1", "key2": {"key3": "value3"}, "key4": ["value4", "value5", "value6"]}"

$(body.key1) -> "value1"

$(body.key2) -> "{"key3": "value3"}"

$(body.key2.key3) -> "value3"

$(body.key4[0]) -> "value4"

$(body.key4[0:2]) -> "{"value4", "value5"}"

# $(header) -> replaced by all headers from the event

$(header) -> "{"One":["one"], "Two":["one","two","three"]}"

$(header.One) -> "one"

$(header.one) -> "one"

$(header.Two) -> "one two three"

$(header.Two[1]) -> "two"

Specifying multiple bindings

You can specify multiple bindings within the Trigger definition in your EventListener. This allows you to reuse as well as mix-and-match your bindings across multiple Trigger definitions. For example, you can create a Trigger with a binding that extracts event data and another binding that provides information on the deployment environment:

apiVersion: triggers.tekton.dev/v1alpha1
kind: TriggerBinding
metadata:
  name: event-binding
spec:
  params:
    - name: gitrevision
      value: $(body.head_commit.id)
    - name: gitrepositoryurl
      value: $(body.repository.url)
---
apiVersion: triggers.tekton.dev/v1alpha1
kind: TriggerBinding
metadata:
  name: prod-env
spec:
  params:
    - name: environment
      value: prod
---
apiVersion: triggers.tekton.dev/v1alpha1
kind: TriggerBinding
metadata:
  name: staging-env
spec:
  params:
    - name: environment
      value: staging
---
apiVersion: triggers.tekton.dev/v1alpha1
kind: EventListener
metadata:
  name: listener
spec:
  triggers:
    - name: prod-trigger
      bindings:
        - ref: event-binding
        - ref: prod-env
      template:
        ref: pipeline-template
    - name: staging-trigger
      bindings:
        - ref: event-binding
        - ref: staging-env
      template:
        ref: pipeline-template

Troubleshooting TriggerBindings

You can use the binding-eval tool to evaluate your TriggerBinding against a specific HTTP request to determine the parameters that Tekton generates from that request when your corresponding Trigger executes.

To install the binding-eval tool use the following command:

$ go get -u github.com/tektoncd/triggers/cmd/binding-eval

Below is an example of using the tool to evaluate a TriggerBinding:

$ cat testdata/triggerbinding.yaml
apiVersion: tekton.dev/v1alpha1
kind: TriggerBinding
metadata:
  name: pipeline-binding
spec:
  params:
  - name: foo
    value: $(body.test)
  - name: bar
    value: $(header.X-Header)

$ cat testdata/http.txt
POST /foo HTTP/1.1
Content-Length: 16
Content-Type: application/json
X-Header: tacocat

{"test": "body"}

$ binding-eval -b testdata/triggerbinding.yaml -r testdata/http.txt
[
  {
    "name": "foo",
    "value": "body"
  },
  {
    "name": "bar",
    "value": "tacocat"
  }
]

Last modified January 1, 0001