Configure a Debezium Reaction

The Drasi Debezium Reaction connector generates a Debezium-compatible data change event for each Added, Updated, or Removed in a Drasi result for a given Continuous Query. The events produced by this Reaction should be analogous to the data change events produced by similar Debezium Connectors, which can be used as a reference model and more detailed commentary.

Requirements

On the computer from where you will create the Drasi Debezium Reaction, you need to install the following software:

• Drasi CLI

Creating the Reaction

To create a Reaction, execute the drasi apply command as follows:

drasi apply -f my-reaction.yaml -n drasi-namespace

The drasi apply command is how you create all new Drasi resources (in this case a Reaction). The -f flag specifies that the definition of the new Reaction is contained in the referenced YAML file my-reaction.yaml and the -n flag specifies the Drasi namespace in which to create the Reaction (Drasi must already be installed in that namespace).

Reaction Definitions

The YAML file passed to drasi apply can contain one or more Reaction definitions. Here is an example of a Drasi Debezium Reaction definition:

apiVersion: v1
kind: Reaction
name: debezium-reaction
spec:
  kind: Debezium
  queries:
    <query-id>:
  properties:
    brokers: <kafka-broker>
    topic: <kafka-topic>
    saslUsername: <username>
    saslPassword: <password>

In this definition:

• the apiVersion must be v1.
• the kind property tells Drasi to create a Reaction resource.
• the spec.kind property tells Drasi the kind of Reaction to create, in this case a Debezium Reaction.
• the name property tells Drasi the identity of the Reaction and must be unique within the scope of Reactions within the target Drasi environment. In the above example, the name of the Reaction is debezium-reaction.

This table describes the other settings in the spec section of the Reaction definition:

Inspecting the Reaction

As soon as the Reaction is created it will start running, subscribing to the specified list of Continuous Queries and processing changes to the Continuous Query results.

You can check the status of the Reaction using the drasi list command:

drasi list reaction

Or including a target namespace:

drasi list reaction -n drasi-namespace

This will return a simple list of all Reactions in the default (or specified) namespace and their overall status. For example:

        ID               | AVAILABLE
-------------------------+------------
    debezium-reaction    | true

If an error has occurred during the creation or operation of a Reaction, the AVAILABLE column will contain the error text instead of true or false.

For more details about the Reaction you can use the drasi describe command:

drasi describe reaction debezium-reaction

This will return the full definition used to create the Reaction along with more detailed status information.

Using the Reaction

The Debezium Reaction output differs from standard Debezium data change events (for example, Vitess events), which typically include four JSON fields: the change event key schema, the actual event key, the change event value schema, and the event value payload. Instead, the Debezium Reaction output contains only a single payload field. This field contains the result from a query change event and its metadata.

We removed the event key fields as the change events themselves do not have primary keys, and we removed the change event value schema field as currently the Drasi Reactions do not have the ability to access the definition of the Continuous Queries. In other words, Drasi is currently unable to generate an accurate schema of a Change Event based on the results from a Continuous Query.

The following skeleton JSON shows the basic format of a standard Debezium change data event:

{
   "payload": { // <1>
        "before":  { ... }, // <2>
        "after": { ... }, // <3>
        "source": { // <4>
            "version": "0.1.6",
            "connector": "drasi",
            "ts_ms": 123456789,
            "seq": 26716600
        },
        "op": "c", // <5>
        "ts_ms": 123456789 // <6>
    }
}

Testing the Reaction

Please navigate this link for guidance on how to test the Debezium Reaction.

Modifying the Reaction

If you want to modify an existing reaction, you can use the drasi apply command to apply the updated YAML file. Ensure that the name of the reaction remains consistent.

Deleting the Reaction

To delete a Reaction you use the drasi delete command. There are two ways to do this.

Firstly, you can specify the type of resource (Reaction) and its name, for example:

drasi delete reaction debezium-reaction

Secondly, you can refer to the YAML file(s) that contain the definitions used to create the Reaction(s):

drasi delete -f my-reaction.yaml <file2.yaml> <file3.yaml> <...>

This is a convenience, especially if a single YAML file contains multiple Reaction definitions.

If the Reaction is not in the default Drasi namespace, you should specific the target namespace using the -n flag as usual:

drasi delete -f my-reaction.yaml -n drasi-namespace