Append processor

Use the Append processor to add a value to an existing array field, or create the field as an array if it doesn't exist.

To use an append processor:

Select Create → Create processor.
Select Append from the Processor menu.
Set Source Field to the field you want to append values to.
Set Target field to the values you want to append to the Source Field.

This functionality uses the Elasticsearch append processor internally, but you configure it in Streamlang. Streamlang doesn't always have 1:1 parity with the ingest processor options and behavior. Refer to Processor limitations and inconsistencies.

YAML reference

In YAML mode, configure the append processor using the following parameters. For the complete Streamlang syntax, refer to the Streamlang reference.

Parameter	Type	Required	Description
`to`	string	Yes	Array field to append to.
`value`	array	Yes	Values to append.
`allow_duplicates`	boolean	No	When `false`, duplicate values are not appended.

- action: append
  to: attributes.tags
  value:
    - processed
    - reviewed