Fault Tolerance Guarantees
This documentation is for an out-of-date version of Apache Flink. We recommend you use the latest stable version.

Fault Tolerance Guarantees of Data Sources and Sinks #

Flink’s fault tolerance mechanism recovers programs in the presence of failures and continues to execute them. Such failures include machine hardware failures, network failures, transient program failures, etc.

Flink can guarantee exactly-once state updates to user-defined state only when the source participates in the snapshotting mechanism. The following table lists the state update guarantees of Flink coupled with the bundled connectors.

Please read the documentation of each connector to understand the details of the fault tolerance guarantees.

Source Guarantees Notes
Apache Kafka exactly once Use the appropriate Kafka connector for your version
AWS Kinesis Streams exactly once
RabbitMQ at most once (v 0.10) / exactly once (v 1.0)
Twitter Streaming API at most once
Google PubSub at least once
Collections exactly once
Files exactly once
Sockets at most once

To guarantee end-to-end exactly-once record delivery (in addition to exactly-once state semantics), the data sink needs to take part in the checkpointing mechanism. The following table lists the delivery guarantees (assuming exactly-once state updates) of Flink coupled with bundled 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

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