// Category: debezium-using
// Type: assembly
// Title: Configuring notifications to report connector status
// ModuleID: configuring-notifications-to-report-connector-status
[id="debezium-notification"]
= {prodname} notifications
ifdef::community[]
:toc:
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:linkattrs:
:icons: font
:source-highlighter: highlight.js

toc::[]

== Overview
endif::community[]

{prodname} notifications provide a mechanism to obtain status information about the connector.
Notifications can be sent to the following channels:

SinkNotificationChannel:: Sends notifications through the Connect API to a configured topic.
LogNotificationChannel:: Notifications are appended to the log.
JmxNotificationChannel:: Notifications are exposed as an attribute in a JMX bean.
ifdef::community[]
Custom:: Notifications are sent to a xref:debezium-notification-custom-channel[custom channel] that you implement.
endif::community[]
ifdef::product[]
For details about {prodname} notifications, see the following topics::

* xref:debezium-notifications-description-of-the-format-of-debezium-notifications[]
* xref:debezium-notifications-types-of-debezium-notifications[]
* xref:debezium-notifications-enabling-debezium-to-emit-events-to-notification-channels[]
//   * xref:debezium-notification-custom-channel[]
endif::product[]

// Type: concept
// ModuleID: debezium-notifications-description-of-the-format-of-debezium-notifications
// Title: Description of the format of {prodname} notifications
[id="debezium-notification-format"]
== {prodname} notification format

Notification messages contain the following information:

|===
|Property |Description

|id
|A unique identifier that is assigned to the notification. For incremental snapshot notifications, the `id` is the same sent with the `execute-snapshot` signal.

|aggregate_type
|The data type of the aggregate root to which a notification is related.
In domain-driven design, exported events should always refer to an aggregate.

|type
|Provides status information about the event specified in the `aggregate_type` field.

|additional_data
|A Map<String,String> with detailed information about the notification.
For an example, see xref:debezium-notifications-about-the-progress-of-incremental-snapshots[{prodname} notifications about the progress of incremental snapshots].
|===

// Type: assembly
// Title: Types of {prodname} notifications
// ModuleID: debezium-notifications-types-of-debezium-notifications
[id="debezium-available-notifications"]
== Available notifications

{prodname} notifications deliver information about the progress of xref:debezium-notifications-about-the-status-of-an-initial-snapshot[initial snapshots] or xref:debezium-notifications-about-the-progress-of-incremental-snapshots[incremental snapshots].

// Title: Example: {prodname} notification that reports on the status of an initial snapshot
[id="debezium-notifications-about-the-status-of-an-initial-snapshot"]
=== {prodname} notifications about the status of an initial snapshot

The following example shows a typical notification that provides the status of an initial snapshot:

[source, json]
----
{
    "id": "5563ae14-49f8-4579-9641-c1bbc2d76f99",
    "aggregate_type": "Initial Snapshot",
    "type": "COMPLETED" <1>
}
----
<1> The type field can contain one of the following values:

* `COMPLETED`
* `ABORTED`
* `SKIPPED`

// Type: reference
// Title: Example: {prodname} notifications that report on the progress of incremental snapshots
[id="debezium-notifications-about-the-progress-of-incremental-snapshots"]
=== {prodname} notifications about the progress of incremental snapshots

The following table shows examples of the different payloads that might be present in notifications that report the status of incremental snapshots:

|===
|Status|Payload

|Start
a|[source, json]
----
  {
      "id":"ff81ba59-15ea-42ae-b5d0-4d74f1f4038f",
      "aggregate_type":"Incremental Snapshot",
      "type":"STARTED",
      "additional_data":{
         "connector_name":"my-connector",
         "data_collections":"table1, table2"
      }
}
----
|Paused
a|[source, json]
----
{
      "id":"068d07a5-d16b-4c4a-b95f-8ad061a69d51",
      "aggregate_type":"Incremental Snapshot",
      "type":"PAUSED",
      "additional_data":{
         "connector_name":"my-connector",
         "data_collections":"table1, table2"
      }
}
----
|Resumed
a|[source, json]
----
 {
   "id":"a9468204-769d-430f-96d2-b0933d4839f3",
   "aggregate_type":"Incremental Snapshot",
   "type":"RESUMED",
   "additional_data":{
      "connector_name":"my-connector",
      "data_collections":"table1, table2"
   }
}
----
|Stopped
a|[source, json]
----
{
   "id":"83fb3d6c-190b-4e40-96eb-f8f427bf482c",
   "aggregate_type":"Incremental Snapshot",
   "type":"ABORTED",
   "additional_data":{
      "connector_name":"my-connector"
   }
}
----
|Processing chunk
a|[source, json]
----
{
   "id":"d02047d6-377f-4a21-a4e9-cb6e817cf744",
   "aggregate_type":"Incremental Snapshot",
   "type":"IN_PROGRESS",
   "additional_data":{
      "connector_name":"my-connector",
      "data_collections":"table1, table2",
      "current_collection_in_progress":"table1",
      "maximum_key":"100",
      "last_processed_key":"50"
   }
}
----
|Snapshot completed for a table
a|[source, json]
----
{
   "id":"6d82a3ec-ba86-4b36-9168-7423b0dd5c1d",
   "aggregate_type":"Incremental Snapshot",
   "type":"TABLE_SCAN_COMPLETED",
   "additional_data":{
      "connector_name":"my-connector",
      "data_collection":"table1, table2",
      "scanned_collection":"table1",
      "total_rows_scanned":"100",
      "status":"SUCCEEDED" // <1>
   }
}
----
<1> The possible values are:
* EMPTY - table is empty
* NO_PRIMARY_KEY - table has no primary key necessary for snapshot
* SKIPPED - snapshot for this kind of table is not supported, check logs for details
* SQL_EXCEPTION - SQL exception caught while processing a snapshot
* SUCCEEDED - snapshot completed successfully
* UNKNOWN_SCHEMA - schema not found for table, check logs for the list of known tables
|Completed
a|[source, json]
----
{
   "id":"6d82a3ec-ba86-4b36-9168-7423b0dd5c1d",
   "aggregate_type":"Incremental Snapshot",
   "type":"COMPLETED",
   "additional_data":{
      "connector_name":"my-connector"
   }
}
----
|===

// Type: assembly
// ModuleID: debezium-notifications-enabling-debezium-to-emit-events-to-notification-channels
// Title: Enabling {prodname} to emit events to notification channels
[id="enabling-debezium-notifications"]
== Enabling {prodname} notifications

To enable {prodname} to emit notifications, specify a list of notification channels by setting the `notification.enabled.channels` configuration property.
By default, the following notification channels are available:

* `sink`
* `log`
* `jmx`

[IMPORTANT]
====
To use the `sink` notification channel, you must also set the `notification.sink.topic.name` configuration property to the name of the topic where you want {prodname} to send notifications.
====

// Type: procedure
// ModuleID: enabling-debezium-notifications-to-report-events-exposed-through-jmx-beans
// Title: Enabling {prodname} notifications to report events exposed through JMX beans
[id="access-debezium-jmx-notifications"]
=== Access to {prodname} JMX notifications

To enable {prodname} to report events that are exposed through JMX beans, complete the following configuration steps:

1. {link-prefix}:{link-debezium-monitoring}#monitoring-debezium[Enable the JMX MBean Server] to expose the notification bean.
2. Add `jmx` to the `notification.enabled.channels` property in the connector configuration.
3. Connect your preferred JMX client to the MBean Server.

Notifications are exposed through the `Notifications` attribute of a bean with the name `debezium.__<connector-type>__.management.notifications.__<server>__`.

The following image shows a notification that reports the start of an incremental snapshot:

image::jmx-notification-attribute.png[Fields in the JMX `Notifications` attribute]

To discard a notification, call the `reset` operation on the bean.

The notifications are also exposed as a JMX notification with type `debezium.notification`.
To enable an application to listen for the JMX notifications that an MBean emits,  link:https://docs.oracle.com/javase/tutorial/jmx/notifs/index.html[subscribe the application to the notifications].

ifdef::community[]
//   Type: assembly
//   Title: Setting up custom channels to deliver {prodname} notifications
//   ModuleID: debezium-notifications-setting-up-custom-channels-to-deliver-notifications
[id="debezium-notification-custom-channel"]
== Custom notification channels

The notification mechanism is designed to be extensible.
You can implement channels as needed to deliver notifications in a manner that works best in your environment.
Adding a notification channel involves several steps:

1. xref:debezium-configuring-custom-notification-channels[Create a Java project for the channel] to implement the channel, and xref:debezium-core-module-dependency[add `{prodname} Core` as a dependency].
2. xref:deploying-a-debezium-custom-notification-channel[Deploy the notification channel].
3. xref:configuring-connectors-to-use-a-custom-notification-channel[Enable connectors to use the custom notification channel by modifying the connector configuration].

//   Type: procedure
//   ModuleID: debezium-notifications-configuring-custom-notification-channels
//   Title: Configuring {prodname} custom notification channels
[id="debezium-configuring-custom-notification-channels"]
=== Configuring custom notification channels

Custom notification channels are Java classes that implement the `io.debezium.pipeline.notification.channels.NotificationChannel` service provider interface (SPI).
For example:
[source,java,indent=0]
----
public interface NotificationChannel {

    String name(); // <1>

    void init(CommonConnectorConfig config); // <2>

    void send(Notification notification); // <3>

    void close(); // <4>
}
----
<1> The name of the channel.
To enable {prodname} to use the channel, specify this name in the connector's `notification.enabled.channels` property.
<2> Initializes specific configuration, variables, or connections that the channel requires.
<3> Sends the notification on the channel.
{prodname} calls this method to report its status.
<4> Closes all allocated resources.
{prodname} calls this method when the connector is stopped.

//   Type: concept
[id="debezium-core-module-dependency"]
=== {prodname} core module dependencies

A custom notification channel Java project has compile dependencies on the {prodname} core module.
You must include these compile dependencies in your project's `pom.xml` file, as shown in the following example:

[source,xml]
----
<dependency>
    <groupId>io.debezium</groupId>
    <artifactId>debezium-core</artifactId>
    <version>${version.debezium}</version> // <1>
</dependency>
----
<1> `${version.debezium}` represents the version of the {prodname} connector.

Declare your implementation in the `META-INF/services/io.debezium.pipeline.notification.channels.NotificationChannel` file.

//   Type: procedure
[id="deploying-a-debezium-custom-notification-channel"]
=== Deploying a custom notification channel

.Prerequisites
* You have a custom notification channel Java program.

.Procedure
* To use a notification channel with a {prodname} connector, export the Java project to a JAR file, and copy the file to the directory that contains the JAR file for each {prodname} connector that you want to use it with. +
 +
For example, in a typical deployment, the {prodname} connector files are stored in subdirectories of a Kafka Connect directory (`/kafka/connect`), with each connector JAR in its own subdirectory (`/kafka/connect/debezium-connector-db2`, `/kafka/connect/debezium-connector-mysql`, and so forth).
To use a signaling channel with a connector, add the converter JAR file to the connector's subdirectory.

NOTE: To use a custom notification channel with multiple connectors, you must place a copy of the notification channel JAR file in each connector subdirectory.

//   Type: procedure
[id="configuring-connectors-to-use-a-custom-notification-channel"]
=== Configuring connectors to use a custom notification channel

In the connector configuration, add the name of the custom notification channel to the `notification.enabled.channels` property.
endif::community[]
