Before image task settings - AWS Database Migration Service

Before image task settings

When writing CDC updates to a data-streaming target like Kinesis or Apache Kafka, you can view a source database row's original values before change by an update. To make this possible, AWS DMS populates a before image of update events based on data supplied by the source database engine. For information about how to use a task configuration file to set task settings, see Task settings example.

To do so, you use the BeforeImageSettings parameter, which adds a new JSON attribute to every update operation with values collected from the source database system.

Make sure to apply BeforeImageSettings only to full load plus CDC tasks or CDC only tasks. Full load plus CDC tasks migrate existing data and replicate ongoing changes. CDC only tasks replicate data changes only.

Don't apply BeforeImageSettings to tasks that are full load only.

Possible options for BeforeImageSettings are the following:

  • EnableBeforeImage – Turns on before imaging when set to true. The default is false.

  • FieldName – Assigns a name to the new JSON attribute. When EnableBeforeImage is true, FieldName is required and can't be empty.

  • ColumnFilter – Specifies a column to add by using before imaging. To add only columns that are part of the table's primary keys, use the default value, pk-only. To add any column that has a before image value, use all. Note that the before image doesn't support large binary object (LOB) data types such as CLOB and BLOB.

The following shows an example of the use of BeforeImageSettings. 

"BeforeImageSettings": {
    "EnableBeforeImage": true,
    "FieldName": "before-image",
    "ColumnFilter": "pk-only"
  }

For information on before image settings for Kinesis, including additional table mapping settings, see Using a before image to view original values of CDC rows for a Kinesis data stream as a target.

For information on before image settings for Kafka, including additional table mapping settings, see Using a before image to view original values of CDC rows for Apache Kafka as a target.