Templating

EXPERIMENTAL

Templates are an experimental feature and therefore subject to change outside of major version releases.

Templates are a way to define new Benthos components (similar to plugins) that are implemented by generating a Benthos config snippet from pre-defined parameter fields. This is useful when a common pattern of Benthos configuration is used but with varying parameters each time.

A template is defined in a YAML file that can be imported when Benthos runs using the flag -t:

benthos -t "./templates/*.yaml" -c ./config.yaml

The template describes the type of the component and configuration fields that can be used to customize it, followed by a Bloblang mapping that translates an object containing those fields into a benthos config structure. This allows you to use logic to generate more complex configurations:

Template

name: aws_sqs_list
type: input

fields:
  - name: urls
    type: string
    kind: list
  - name: region
    type: string
    default: us-east-1

mapping: |
  root.broker.inputs = this.urls.map_each(url -> {
    "aws_sqs": {
      "url": url,
      "region": this.region,
    }
  })

Config

input:
  aws_sqs_list:
    urls:
      - https://sqs.us-east-2.amazonaws.com/123456789012/MyQueue1
      - https://sqs.us-east-2.amazonaws.com/123456789012/MyQueue2

pipeline:
  processors:
    - mapping: |
        root.id = uuid_v4()
        root.foo = this.inner.foo
        root.body = this.outer

Result

input:
  broker:
    inputs:
      - aws_sqs:
          url: https://sqs.us-east-2.amazonaws.com/123456789012/MyQueue1
          region: us-east-1
      - aws_sqs:
          url: https://sqs.us-east-2.amazonaws.com/123456789012/MyQueue2
          region: us-east-1

pipeline:
  processors:
    - mapping: |
        root.id = uuid_v4()
        root.foo = this.inner.foo
        root.body = this.outer

You can see more examples of templates at https://github.com/benthosdev/benthos/tree/main/config/template_examples.

Fields

The schema of a template file is as follows:

name

The name of the component this template will create.

Type: string

type

The type of the component this template will create.

Type: string
Options: cache, input, output, processor, rate_limit.

status

The stability of the template describing the likelihood that the configuration spec of the template, or it's behaviour, will change.

Type: string
Default: "stable"

Option	Summary
stable	This template is stable and will therefore not change in a breaking way outside of major version releases.
beta	This template is beta and will therefore not change in a breaking way unless a major problem is found.
experimental	This template is experimental and therefore subject to breaking changes outside of major version releases.

categories

An optional list of tags, which are used for arbitrarily grouping components in documentation.

Type: list of string
Default: []

summary

A short summary of the component.

Type: string
Default: ""

description

A longer form description of the component and how to use it.

Type: string
Default: ""

fields

The configuration fields of the template, fields specified here will be parsed from a Benthos config and will be accessible from the template mapping.

Type: list of object

fields[].name

The name of the field.

Type: string

fields[].description

A description of the field.

Type: string
Default: ""

fields[].type

The scalar type of the field.

Type: string

Option	Summary
string	standard string type
int	standard integer type
float	standard float type
bool	a boolean true/false
unknown	allows for nesting arbitrary configuration inside of a field

fields[].kind

The kind of the field.

Type: string
Default: "scalar"
Options: scalar, map, list.

fields[].default

An optional default value for the field. If a default value is not specified then a configuration without the field is considered incorrect.

Type: unknown

fields[].advanced

Whether this field is considered advanced.

Type: bool
Default: false

mapping

A Bloblang mapping that translates the fields of the template into a valid Benthos configuration for the target component type.

Type: string

metrics_mapping

An optional Bloblang mapping that allows you to rename or prevent certain metrics paths from being exported. For more information check out the metrics documentation. When metric paths are created, renamed and dropped a trace log is written, enabling TRACE level logging is therefore a good way to diagnose path mappings.

Invocations of this mapping are able to reference a variable $label in order to obtain the value of the label provided to the template config. This allows you to match labels with the root of the config.

Type: string
Default: ""

# Examples

metrics_mapping: this.replace("input", "source").replace("output", "sink")

metrics_mapping: |-
  root = if ![
    "input_received",
    "input_latency",
    "output_sent"
  ].contains(this) { deleted() }

tests

Optional unit test definitions for the template that verify certain configurations produce valid configs. These tests are executed with the command benthos template lint.

Type: list of object
Default: []

tests[].name

A name to identify the test.

Type: string

tests[].config

A configuration to run this test with, the config resulting from applying the template with this config will be linted.

Type: object

tests[].expected

An optional configuration describing the expected result of applying the template, when specified the result will be diffed and any mismatching fields will be reported as a test error.

Type: object