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name: confluent-kafka-connect description: Kafka Connect integration expert. Covers source and sink connectors, JDBC, Elasticsearch, S3, Debezium CDC, SMT (Single Message Transforms), connector configuration, and data pipeline patterns. Activates for kafka connect, connectors, source connector, sink connector, jdbc connector, debezium, smt, data pipeline, cdc.

Confluent Kafka Connect Skill

Expert knowledge of Kafka Connect for building data pipelines with source and sink connectors.

What I Know

Connector Types

Source Connectors (External System → Kafka):

• JDBC Source: Databases → Kafka
• Debezium: CDC (MySQL, PostgreSQL, MongoDB) → Kafka
• S3 Source: AWS S3 files → Kafka
• File Source: Local files → Kafka

Sink Connectors (Kafka → External System):

• JDBC Sink: Kafka → Databases
• Elasticsearch Sink: Kafka → Elasticsearch
• S3 Sink: Kafka → AWS S3
• HDFS Sink: Kafka → Hadoop HDFS

Single Message Transforms (SMTs):

• Field operations: Insert, Mask, Replace, TimestampConverter
• Routing: RegexRouter, TimestampRouter
• Filtering: Filter, Predicates

When to Use This Skill

Activate me when you need help with:

• Connector setup ("Configure JDBC connector")
• CDC patterns ("Debezium MySQL CDC")
• Data pipelines ("Stream database changes to Kafka")
• SMT transforms ("Mask sensitive fields")
• Connector troubleshooting ("Connector task failed")

Common Patterns

Pattern 1: JDBC Source (Database → Kafka)

Use Case: Stream database table changes to Kafka

Configuration:

{
  "name": "jdbc-source-users",
  "config": {
    "connector.class": "io.confluent.connect.jdbc.JdbcSourceConnector",
    "tasks.max": "1",
    "connection.url": "jdbc:postgresql://localhost:5432/mydb",
    "connection.user": "postgres",
    "connection.password": "password",
    "mode": "incrementing",
    "incrementing.column.name": "id",
    "topic.prefix": "postgres-",
    "table.whitelist": "users,orders",
    "poll.interval.ms": "5000"
  }
}

Modes:

• incrementing: Track by auto-increment ID
• timestamp: Track by timestamp column
• timestamp+incrementing: Both (most reliable)

Pattern 2: Debezium CDC (MySQL → Kafka)

Use Case: Capture all database changes (INSERT/UPDATE/DELETE)

Configuration:

{
  "name": "debezium-mysql-cdc",
  "config": {
    "connector.class": "io.debezium.connector.mysql.MySqlConnector",
    "tasks.max": "1",
    "database.hostname": "localhost",
    "database.port": "3306",
    "database.user": "debezium",
    "database.password": "password",
    "database.server.id": "1",
    "database.server.name": "mysql",
    "database.include.list": "mydb",
    "table.include.list": "mydb.users,mydb.orders",
    "schema.history.internal.kafka.bootstrap.servers": "localhost:9092",
    "schema.history.internal.kafka.topic": "schema-changes.mydb"
  }
}

Output Format (Debezium Envelope):

{
  "before": null,
  "after": {
    "id": 1,
    "name": "John Doe",
    "email": "john@example.com"
  },
  "source": {
    "version": "1.9.0",
    "connector": "mysql",
    "name": "mysql",
    "ts_ms": 1620000000000,
    "snapshot": "false",
    "db": "mydb",
    "table": "users",
    "server_id": 1,
    "gtid": null,
    "file": "mysql-bin.000001",
    "pos": 12345,
    "row": 0,
    "thread": null,
    "query": null
  },
  "op": "c",  // c=CREATE, u=UPDATE, d=DELETE, r=READ
  "ts_ms": 1620000000000
}

Pattern 3: JDBC Sink (Kafka → Database)

Use Case: Write Kafka events to PostgreSQL

Configuration:

{
  "name": "jdbc-sink-enriched-orders",
  "config": {
    "connector.class": "io.confluent.connect.jdbc.JdbcSinkConnector",
    "tasks.max": "3",
    "topics": "enriched-orders",
    "connection.url": "jdbc:postgresql://localhost:5432/analytics",
    "connection.user": "postgres",
    "connection.password": "password",
    "auto.create": "true",
    "auto.evolve": "true",
    "insert.mode": "upsert",
    "pk.mode": "record_value",
    "pk.fields": "order_id",
    "table.name.format": "orders_${topic}"
  }
}

Insert Modes:

• insert: Append only (fails on duplicate)
• update: Update only (requires PK)
• upsert: INSERT or UPDATE (recommended)

Pattern 4: S3 Sink (Kafka → AWS S3)

Use Case: Archive Kafka topics to S3

Configuration:

{
  "name": "s3-sink-events",
  "config": {
    "connector.class": "io.confluent.connect.s3.S3SinkConnector",
    "tasks.max": "3",
    "topics": "user-events,order-events",
    "s3.region": "us-east-1",
    "s3.bucket.name": "my-kafka-archive",
    "s3.part.size": "5242880",
    "flush.size": "1000",
    "rotate.interval.ms": "60000",
    "rotate.schedule.interval.ms": "3600000",
    "timezone": "UTC",
    "format.class": "io.confluent.connect.s3.format.json.JsonFormat",
    "partitioner.class": "io.confluent.connect.storage.partitioner.TimeBasedPartitioner",
    "path.format": "'year'=YYYY/'month'=MM/'day'=dd/'hour'=HH",
    "locale": "US",
    "timestamp.extractor": "Record"
  }
}

Partitioning (S3 folder structure):

s3://my-kafka-archive/
  topics/user-events/year=2025/month=01/day=15/hour=10/
    user-events+0+0000000000.json
    user-events+0+0000001000.json
  topics/order-events/year=2025/month=01/day=15/hour=10/
    order-events+0+0000000000.json

Pattern 5: Elasticsearch Sink (Kafka → Elasticsearch)

Use Case: Index Kafka events for search

Configuration:

{
  "name": "elasticsearch-sink-logs",
  "config": {
    "connector.class": "io.confluent.connect.elasticsearch.ElasticsearchSinkConnector",
    "tasks.max": "3",
    "topics": "application-logs",
    "connection.url": "http://localhost:9200",
    "connection.username": "elastic",
    "connection.password": "password",
    "key.ignore": "true",
    "schema.ignore": "true",
    "type.name": "_doc",
    "index.write.wait_for_active_shards": "1"
  }
}

Single Message Transforms (SMTs)

Transform 1: Mask Sensitive Fields

Use Case: Hide email/phone in Kafka topics

Configuration:

{
  "transforms": "maskEmail",
  "transforms.maskEmail.type": "org.apache.kafka.connect.transforms.MaskField$Value",
  "transforms.maskEmail.fields": "email,phone"
}

Before:

{"id": 1, "name": "John", "email": "john@example.com", "phone": "555-1234"}

After:

{"id": 1, "name": "John", "email": null, "phone": null}

Transform 2: Add Timestamp

Use Case: Add processing timestamp to all messages

Configuration:

{
  "transforms": "insertTimestamp",
  "transforms.insertTimestamp.type": "org.apache.kafka.connect.transforms.InsertField$Value",
  "transforms.insertTimestamp.timestamp.field": "processed_at"
}

Transform 3: Route by Field Value

Use Case: Route high-value orders to separate topic

Configuration:

{
  "transforms": "routeByValue",
  "transforms.routeByValue.type": "org.apache.kafka.connect.transforms.RegexRouter",
  "transforms.routeByValue.regex": "(.*)",
  "transforms.routeByValue.replacement": "$1-high-value",
  "transforms.routeByValue.predicate": "isHighValue",
  "predicates": "isHighValue",
  "predicates.isHighValue.type": "org.apache.kafka.connect.transforms.predicates.TopicNameMatches",
  "predicates.isHighValue.pattern": "orders"
}

Transform 4: Flatten Nested JSON

Use Case: Flatten nested structures for JDBC sink

Configuration:

{
  "transforms": "flatten",
  "transforms.flatten.type": "org.apache.kafka.connect.transforms.Flatten$Value",
  "transforms.flatten.delimiter": "_"
}

Before:

{
  "user": {
    "id": 1,
    "profile": {
      "name": "John",
      "email": "john@example.com"
    }
  }
}

After:

{
  "user_id": 1,
  "user_profile_name": "John",
  "user_profile_email": "john@example.com"
}

Best Practices

1. Use Idempotent Connectors

✅ DO:

// JDBC Sink with upsert mode
{
  "insert.mode": "upsert",
  "pk.mode": "record_value",
  "pk.fields": "id"
}

❌ DON'T:

// WRONG: insert mode (duplicates on restart!)
{
  "insert.mode": "insert"
}

2. Monitor Connector Status

# Check connector status
curl http://localhost:8083/connectors/jdbc-source-users/status

# Check task status
curl http://localhost:8083/connectors/jdbc-source-users/tasks/0/status

3. Use Schema Registry

✅ DO:

{
  "value.converter": "io.confluent.connect.avro.AvroConverter",
  "value.converter.schema.registry.url": "http://localhost:8081"
}

4. Configure Error Handling

{
  "errors.tolerance": "all",
  "errors.log.enable": "true",
  "errors.log.include.messages": "true",
  "errors.deadletterqueue.topic.name": "dlq-jdbc-sink",
  "errors.deadletterqueue.context.headers.enable": "true"
}

Connector Management

Deploy Connector

# Create connector via REST API
curl -X POST http://localhost:8083/connectors \
  -H "Content-Type: application/json" \
  -d @jdbc-source.json

# Update connector
curl -X PUT http://localhost:8083/connectors/jdbc-source-users/config \
  -H "Content-Type: application/json" \
  -d @jdbc-source.json

Monitor Connectors

# List all connectors
curl http://localhost:8083/connectors

# Get connector info
curl http://localhost:8083/connectors/jdbc-source-users

# Get connector status
curl http://localhost:8083/connectors/jdbc-source-users/status

# Get connector tasks
curl http://localhost:8083/connectors/jdbc-source-users/tasks

Pause/Resume Connectors

# Pause connector
curl -X PUT http://localhost:8083/connectors/jdbc-source-users/pause

# Resume connector
curl -X PUT http://localhost:8083/connectors/jdbc-source-users/resume

# Restart connector
curl -X POST http://localhost:8083/connectors/jdbc-source-users/restart

# Restart task
curl -X POST http://localhost:8083/connectors/jdbc-source-users/tasks/0/restart

Common Issues & Solutions

Issue 1: Connector Task Failed

Symptoms: Task state = FAILED

Solutions:

1. Check connector logs: docker logs connect-worker
2. Validate configuration: curl http://localhost:8083/connector-plugins/<class>/config/validate
3. Restart task: curl -X POST .../tasks/0/restart

Issue 2: Schema Evolution Error

Error: Incompatible schema detected

Solution: Enable auto-evolution:

{
  "auto.create": "true",
  "auto.evolve": "true"
}

Issue 3: JDBC Connection Pool Exhausted

Error: Could not get JDBC connection

Solution: Increase pool size:

{
  "connection.attempts": "3",
  "connection.backoff.ms": "10000"
}

References

• Kafka Connect Documentation: https://kafka.apache.org/documentation/#connect
• Confluent Hub: https://www.confluent.io/hub/
• Debezium Documentation: https://debezium.io/documentation/
• Transform Reference: https://kafka.apache.org/documentation/#connect_transforms

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Invoke me when you need Kafka Connect, connectors, CDC, or data pipeline expertise!