Why this matters
- VaultCommerce uses Kafka Streams for fraud; Flink for cross-region join of orders + clickstream (2TB state).
- ksqlDB offers SQL over Kafka topics — fast analytics prototypes.
- Flink provides event-time watermarks, savepoints, and true distributed state.
- Know when to escalate — not every team needs Flink day one.
ksqlDB use cases
Persistent queries: CREATE STREAM orders AS SELECT * FROM order_raw WHERE total > 1000. Materialized tables for pull queries. VaultCommerce analytics team prototypes dashboards in ksqlDB before porting to Streams for production hardening.
Key points
- ksqlDB — Confluent SQL engine over Kafka topics
- Persistent query — continuous SQL statement as running job
- Flink checkpoint — consistent distributed state snapshot
- Savepoint — manual checkpoint for upgrade/migration
- State backend — RocksDB or heap; S3 for checkpoint storage
Apache Flink
Distributed runtime with checkpointing to S3. VaultCommerce Flink job joins orders KTable with clicks stream on customerId with 1-hour state TTL. Savepoints enable code upgrade without losing state.
VaultCommerce rollout checklist
Before promoting changes that touch the VaultCommerce order and payment event backbone, run the staging KRaft cluster (Kafka 3.7+, Schema Registry 7.x) through a 10k events/min soak test. Compare producer request latency p99 and consumer lag per group against the pre-deploy baseline. Streams for embedded JVM topologies. Document the change in the internal topic registry, attach Grafana screenshots to the change ticket, and keep an engineer on lag dashboards for 30 minutes after production rollout — roll back the service release before altering broker-level settings if lag or under-replicated partitions spike.
-- VaultCommerce ksqlDB — high-value order stream (prototype)
CREATE STREAM vaultcommerce_orders (
order_id VARCHAR KEY,
customer_id VARCHAR,
total_cents BIGINT,
placed_at TIMESTAMP
) WITH (KAFKA_TOPIC='vaultcommerce.orders.placed.v1', VALUE_FORMAT='AVRO');
CREATE STREAM high_value_orders AS
SELECT * FROM vaultcommerce_orders
WHERE total_cents > 50000
EMIT CHANGES;
Quick recall
Everything you need if you only revisit this box.
- Streams for embedded JVM topologies.
- ksqlDB for SQL prototyping.
- Flink for large state, joins, and savepoint upgrades.
Test yourself
Answer these before moving on — recall is what makes it stick.