= Debezium Spring Boot Starter

Spring Boot Starter for easy integration of https://debezium.io[Debezium] in Spring Boot applications.

To use it you just add the `cdc-debezium-boot-starter` dependency to your application POM and implement your own `Consumer<SourceRecord>` handler to process the incoming database change events. Follow the link below for further instructions.

https://en.wikipedia.org/wiki/Change_data_capture[Change Data Capture] (CDC) Spring Boot Starter that allows capturing change events from various databases including `MySQL`, `PostgreSQL`, `MongoDB`, `Oracle` and `SQL Server`.

== Quick Start

https://start.spring.io/[Start new Spring Boot project] and add the following starter dependency to activate the CDC:

[source, xml]
----
<dependency>
    <groupId>org.springframework.cloud.fn</groupId>
    <artifactId>cdc-debezium-boot-starter</artifactId>
    <version>1.0.0-SNAPSHOT</version>
</dependency>
----

NOTE: for MySQL you need to adjust the mysql client version to `mysql:mysql-connector-java:8.0.13`.

The CDC starter setups an embedded https://debezium.io/documentation/reference/0.10/connectors/index.html[debezium connector] to capture the database changes.

Then implement a `Consumer<SourceRecord>` bean handler to receive and process the CDC notifications:

[source, java]
----
@Bean
public Consumer<SourceRecord> mySourceRecordConsumer( # <1>
        Function<SourceRecord, byte[]> keySerializer, # <2>
        Function<SourceRecord, byte[]> valueSerializer) { # <3>

    return sourceRecord -> {
        System.out.println(sourceRecord.topic() # <4>
            + " : " + new String(keySerializer.apply(sourceRecord)) # <5>
            + " : " + new String(valueSerializer.apply(sourceRecord))); # <6>
    };
}
----

<1> CDC event listener that is called on every data change.
<2> Optional keySerializer converter that allows to serialize the keys of the SourceRecord into a compact binary format.
<3> Optional valueSerializer converter (by default JsonConverter) that allows to serialize the SourceRecord into a compact binary format.
<4> The `topic()` provides a logical identifier of the changed data (e.g. cdc-name.DB-name.table-name)
<5> Convert kay to text message using the keySerializer
<6> Convert payload to JSON message using the valueSerializer.

NOTE: you may have to add `@AutoConfigureBefore(CdcAutoConfiguration.class)` to your Boot class to ensure that your record consumer overrides the default handlers.

Above handler will produce output messages like this:
[source, bash]
----
my-app-connector.inventory.addresses : {"id":10,"customer_id":1001,"street":"3183 Moore Avenue","city":"Euless","state":"Texas","zip":"76036","type":"SHIPPING"}
my-app-connector.inventory.customers : {"id":1004,"first_name":"Anne","last_name":"Kretchmar","email":"annek@noanswer.org"}
my-app-connector.inventory.orders : {"order_number":10001,"order_date":16816,"purchaser":1001,"quantity":1,"product_id":102}
my-app-connector.inventory.products : {"id":109,"name":"spare tire","description":"24 inch spare tire","weight":22.200000762939453}
my-app-connector.inventory.products_on_hand : {"product_id":101,"quantity":3}
----

All Debezium connector properties are supported. Just prefix those properties with `cdc.config` prefix.

Following snipped shows how to configure the https://debezium.io/docs/connectors/mysql/[MySqlConnector] to connect to a local MySQL database run via the `debezium/example-mysql` docker image:
[source, bash]
----
docker run -it --rm --name mysql -p 3306:3306 -e MYSQL_ROOT_PASSWORD=debezium -e MYSQL_USER=mysqluser -e MYSQL_PASSWORD=mysqlpw debezium/example-mysql:1.0
----

[TIP]
====
(optional) Use `mysql` client to connected to the database and to create a `debezium` user with required credentials:
[source, bash]
----
docker run -it --rm --name mysqlterm --link mysql --rm mysql:5.7 sh -c 'exec mysql -h"$MYSQL_PORT_3306_TCP_ADDR" -P"$MYSQL_PORT_3306_TCP_PORT" -uroot -p"$MYSQL_ENV_MYSQL_ROOT_PASSWORD"'
mysql> GRANT SELECT, RELOAD, SHOW DATABASES, REPLICATION SLAVE, REPLICATION CLIENT ON *.* TO 'debezium' IDENTIFIED BY 'dbz';
----
====

Configure `cdc-debezium-boot-starter` for consuming cdc events from the MySQL:

[source]
----
cdc.name=my-sql-connector # <1>

cdc.connector=mysql # <2>

cdc.config.database.server.id=85744 # <3>
cdc.config.database.server.name=my-app-connector # <3>
cdc.config.database.user=debezium # <3>
cdc.config.database.password=dbz # <3>
cdc.config.database.hostname=localhost # <3>
cdc.config.database.port=3306 # <3>

cdc.schema=false # <4>

cdc.flattening.enabled=true # <5>
----

<1> Metadata used to identify and dispatch the events received by this cdc consumer instance.
<2> Configures the CDC Source to use https://debezium.io/docs/connectors/mysql/[MySqlConnector]. (equivalent to setting `cdc.config.connector.class=io.debezium.connector.mysql.MySqlConnector`).
<3> Connector specific configurations. MySQL server logical name, connect location and access credentials.
<4> Do not serialize the record's schema in the output messages.
<5> Enables the https://debezium.io/docs/configuration/event-flattening/[CDC Event Flattening] feature.

The full list of properties:

==== Options

//tag::configuration-properties[]
$$cdc.config$$:: $$Spring pass-trough wrapper for debezium configuration properties. All properties with a 'cdc.config.' prefix are native Debezium properties. The prefix is removed, converting them into Debezium io.debezium.config.Configuration.$$ *($$Map<String, String>$$, default: `$$<none>$$`)*
$$cdc.connector$$:: $$Shortcut for the cdc.config.connector.class property. Either of those can be used as long as they do not contradict with each other.$$ *($$ConnectorType$$, default: `$$<none>$$`, possible values: `mysql`,`postgres`,`mongodb`,`oracle`,`sqlserver`)*
$$cdc.flattening.add-fields$$:: $$Comma separated list of metadata fields to add to the flattened message. The fields will be prefixed with "__" or "__[<]struct]__", depending on the specification of the struct.$$ *($$String$$, default: `$$<none>$$`)*
$$cdc.flattening.add-headers$$:: $$Comma separated list specify a list of metadata fields to add to the header of the flattened message. The fields will be prefixed with "__" or "__[struct]__".$$ *($$String$$, default: `$$<none>$$`)*
$$cdc.flattening.delete-handling-mode$$:: $$Options for handling deleted records: (1) none - pass the records through, (2) drop - remove the records and (3) rewrite - add a '__deleted' field to the records.$$ *($$DeleteHandlingMode$$, default: `$$<none>$$`, possible values: `drop`,`rewrite`,`none`)*
$$cdc.flattening.drop-tombstones$$:: $$By default Debezium generates tombstone records to enable Kafka compaction on deleted records. The dropTombstones can suppress the tombstone records.$$ *($$Boolean$$, default: `$$true$$`)*
$$cdc.flattening.enabled$$:: $$Enable flattening the source record events (https://debezium.io/docs/configuration/event-flattening).$$ *($$Boolean$$, default: `$$true$$`)*
$$cdc.name$$:: $$Unique name for this sourceConnector instance.$$ *($$String$$, default: `$$<none>$$`)*
$$cdc.offset.commit-timeout$$:: $$Maximum number of milliseconds to wait for records to flush and partition offset data to be committed to offset storage before cancelling the process and restoring the offset data to be committed in a future attempt.$$ *($$Duration$$, default: `$$5000ms$$`)*
$$cdc.offset.flush-interval$$:: $$Interval at which to try committing offsets. The default is 1 minute.$$ *($$Duration$$, default: `$$60000ms$$`)*
$$cdc.offset.policy$$:: $$Offset storage commit policy.$$ *($$OffsetPolicy$$, default: `$$<none>$$`)*
$$cdc.offset.storage$$:: $$Kafka connector tracks the number processed records and regularly stores the count (as "offsets") in a preconfigured metadata storage. On restart the connector resumes the reading from the last recorded source offset.$$ *($$OffsetStorageType$$, default: `$$<none>$$`, possible values: `memory`,`file`,`kafka`,`metadata`)*
$$cdc.schema$$:: $$Include the schema's as part of the outbound message.$$ *($$Boolean$$, default: `$$false$$`)*
//end::configuration-properties[]
