Debezium CDC with Moose & Drizzle

Easy-to-run demo of a CDC pipeline using Debezium (Kafka Connect), PostgreSQL, Redpanda, Apicurio (JSON Schema), and ClickHouse.

🚀 Quick Start

Prerequisites

• Docker + Docker Compose
• Node.js 20+ and pnpm
• Moose CLI: npm i -g @514labs/moose-cli

1) Clone & Install

gh repo clone okane16/debezium-cdc
cd debezium-cdc
pnpm install

2) Start Dev Environment (keep this terminal open)

moose dev

This starts the Moose dev server, which:

• Spins up local ClickHouse and Redpanda
• Starts all CDC services defined in docker-compose.dev.override.yaml (PostgreSQL, Debezium Kafka Connect, Apicurio Schema Registry)
• Manages lifecycle: when you stop the dev server, these containers are torn down automatically

On first start, Moose runs the script configured in moose.config.toml:

[http_server_config]
...
on_first_start_script = "./setup-cdc.sh"

What setup-cdc.sh does:

• Pushes the Drizzle schema from app/oltp/schema.ts to the local PostgreSQL
• Seeds tables with random sample data
• Creates or updates the Debezium postgres connector, using the JSON config in postgres-connector.json

You’ll see the script’s output and subsequent CDC logs in the same terminal where you ran moose dev.

3) Seed Data (new terminal)

The startup script will seed 10 rows per table. You can seed more rows by running the following commands:

# Seed all tables (10 records each)
pnpm db:seed

# Or seed specific tables / counts
pnpm db:seed:customers 100
pnpm db:seed:another 50

# Clear data
pnpm db:clear
pnpm db:clear:customers
pnpm db:clear:another

4) Optional: Open Drizzle Studio

The Drizzle Studio GUI lets you easily view, edit, and delete rows in your PostgreSQL database tables. This is a great way to trigger CDC events and observe the data flowing into ClickHouse.

pnpm db:studio  # http://local.drizzle.studio/

📁 app/ Structure

app/
├── cdc/
│   ├── 1-sources/                  # CDC Kafka topics
│   │   ├── externalTopics.ts       # AUTO-GENERATED by `moose kafka pull`
│   │   └── typed-topics.ts         # Typed wrappers around generated topics
│   ├── 2-transforms/               # CDC transforms
│   │   ├── payload-handler.ts      # Generic CDC handler (insert/update/delete)
│   │   ├── customer-addresses.ts   # Per-table transform
│   │   └── another-table.ts        # Per-table transform
│   └── 3-destinations/             # ClickHouse targets
│       ├── olap-tables.ts          # Click table definitions (ReplacingMergeTree)
│       └── intermediate-streams.ts # Streaming buffers to store results from transforms before writing to ClickHouse tables
├── oltp/
│   ├── connection.ts               # PostgreSQL connection (Drizzle)
│   ├── schema.ts                   # Drizzle schema
│   └── seed.ts                     # Seeding CLI
├── models.ts                       # Shared types
└── index.ts                        # Entry point

Numbered folders visualize flow: 1-sources → 2-transforms → 3-destinations.

🔧 Useful Commands

# App
moose dev                 # Start Moose dev environment
moose build               # Build for production
moose truncate --all      # Clear all ClickHouse tables

# Data
pnpm db:seed             # Seed all tables (default: 10 each)
pnpm db:seed:customers 100
pnpm db:seed:another 50
pnpm db:clear            # Clear all tables
pnpm db:studio           # Open Drizzle Studio

# Kafka (inside Redpanda container)
pnpm dev:kafka:pull # Pull Kafka topics from Redpanda
docker exec debezium-cdc-redpanda-1 rpk topic list
docker exec debezium-cdc-redpanda-1 rpk topic consume pg-cdc.public.customer_addresses --num 5
docker exec debezium-cdc-redpanda-1 rpk topic consume pg-cdc.public.another_table --num 5

⚙️ Configuration

# app/oltp/connection.ts defaults
DB_HOST=localhost
DB_PORT=5433
DB_NAME=test-db
DB_USER=postgres
DB_PASSWORD=postgres

Debezium connector (see postgres-connector.json) streams:

• public.customer_addresses → pg-cdc.public.customer_addresses
• public.another_table → pg-cdc.public.another_table

Debezium connector config: most important settings

• topic.prefix — Prefix for all emitted Kafka topics. Final topics look like <topic.prefix>.public.<table>.
• table.include.list — Which tables to capture. Use schema-qualified names or patterns (e.g., public.* or public.customer_addresses,public.another_table).

Example:

{
  "topic.prefix": "pg-cdc",
  "table.include.list": "public.*"
}

See postgres-connector.jsonc for an annotated, human-friendly version. The actual file used by the setup script is postgres-connector.json (must be plain JSON, no comments).

🐛 Troubleshooting

• If setup-cdc.sh fails: chmod +x setup-cdc.sh then pnpm dev
• Check connector: curl http://localhost:8084/connectors/postgres-connector/status
• Verify topics: cat app/cdc/1-sources/externalTopics.ts

📚 References

• Debezium: https://debezium.io/
• Moose: https://docs.moosejs.com/
• Drizzle ORM: https://orm.drizzle.team/
• Redpanda: https://docs.redpanda.com/