Fault Tolerance Guarantees of Data Sources and Sinks

Sink	Guarantees	Notes
Elasticsearch	at least once
Kafka producer	at least once / exactly once	exactly once with transactional producers (v 0.11+)
Cassandra sink	at least once / exactly once	exactly once only for idempotent updates
AWS Kinesis Streams	at least once
File sinks	exactly once
Socket sinks	at least once
Standard output	at least once
Redis sink	at least once