S3 sink connector by Aiven naming and data formats

The Apache Kafka Connect® S3 sink connector by Aiven enables you to move data from an Aiven for Apache Kafka® cluster to Amazon S3 for long term storage. The following document describes advanced parameters defining the naming and data formats.


Aiven provides two version of S3 sink connector: one developed by Aiven, another developed by Confluent.

This article is about the Aiven version. Documentation for the Confluent version is available at the dedicated page.

S3 naming format

The Apache Kafka Connect® S3 sink connector by Aiven stores a series of files as objects in the specified S3 bucket. By default, each object is named using the pattern:


The placeholders are the following:

  • AWS_S3_PREFIX: Can be any string and use placeholders like {{ utc_date }} and {{ local_date }} to create different files for each date.

  • TOPIC_NAME: Name of the topic to be pushed to S3

  • PARTITION_NUMBER: Topic partitions number

  • START_OFFSET: File starting offset

  • FILE_EXTENSION: The file extension depends on the compression defined in the file.compression.type parameter. The gz extension is generated when using the gzip compression.


You can customise the S3 object naming and how records are grouped into files, see the documentation in GitHub on the file naming format for further details.

The Apache Kafka Connect® connector creates one file per period defined by the offset.flush.interval.ms parameter. The file is generated for every partition that has received at least one new message during the period. The setting defaults to 60 seconds.

S3 data format

By default, data is stored in one record per line in S3 in CSV format.


You can change the output data format to JSON or Parquet by setting the format.output.type. More details can be found in the GitHub connector repository documentation

You can define the output data fields with the format.output.fields connector configuration. The message key and value, if included in the output, are encoded in Base64.

For example, setting format.output.fields to value,key,timestamp results in rows in the S3 files like the following:



You can disable the Base64 encoding by setting the format.output.fields.value.encoding to none