The out_s3 TimeSliced Output plugin writes records into the Amazon S3 cloud object storage service. By default, it creates files on an hourly basis. This means that when you first import records using the plugin, no file is created immediately. The file will be created when the time_slice_format condition has been met. To change the output frequency, please modify the time_slice_format value. This document doesn't describe all parameters. If you want to know full features, check the Further Reading section.


out_s3 is included in td-agent by default. Fluentd gem users will need to install the fluent-plugin-s3 gem using the following command.

$ fluent-gem install fluent-plugin-s3

Example Configuration

<match pattern>
  @type s3

  aws_key_id YOUR_AWS_KEY_ID
  aws_sec_key YOUR_AWS_SECRET_KEY
  s3_bucket YOUR_S3_BUCKET_NAME
  s3_region ap-northeast-1
  path logs/
  buffer_path /var/log/fluent/s3

  time_slice_format %Y%m%d%H
  time_slice_wait 10m

  buffer_chunk_limit 256m

Please see the Store Apache Logs into Amazon S3 article for real-world use cases.

Please see the Config File article for the basic structure and syntax of the configuration file.

Please make sure that you have enough space in the buffer_path directory. Running out of disk space is a problem frequently reported by users.


type (required)

The value must be s3.

aws_key_id (required/optional)

The AWS access key id. This parameter is required when your agent is not running on an EC2 instance with an IAM Instance Profile.

aws_sec_key (required/optional)

The AWS secret key. This parameter is required when your agent is not running on an EC2 instance with an IAM Instance Profile.

s3_bucket (required)

The Amazon S3 bucket name.

buffer_path (required)

The path prefix of the log buffer files.


The Amazon S3 region name. Please select the appropriate region name and confirm that your bucket has been created in the correct region. Here are the region examples.

  • us-east-1

  • us-west-1

  • eu-central-1

  • ap-southeast-1

  • sa-east-1

The full list can be found official AWS document.


This option is deprecated because latest aws-sdk ignores this option. Please use s3_region instead.

The Amazon S3 enpoint name. Please select the appropriate endpoint name from the list below and confirm that your bucket has been created in the correct region.

  • s3.amazonaws.com

  • s3-us-west-1.amazonaws.com

  • s3-us-west-2.amazonaws.com

  • s3.sa-east-1.amazonaws.com

  • s3-eu-west-1.amazonaws.com

  • s3-ap-southeast-1.amazonaws.com

  • s3-ap-northeast-1.amazonaws.com

The most recent versions of the endpoints can be found here.


The format of the S3 object. The default is out_file.

See formatter article for more detail.


The format of the time written in files. The default format is ISO-8601.


The path prefix of the files on S3. The default is "" (no prefix).

The actual path on S3 will be: "{path}{time_slice_format}_{sequential_index}.gz" (see `s3_object_key_format`)


The actual S3 path. The default value is %{path}%{time_slice}_%{index}.%{file_extension}, which is interpolated to the actual path (ex: Ruby's variable interpolation).

  • path: the value of the path parameter above

  • time_slice: the time string as formatted by time_slice_format

  • index: the index for the given path. Incremented per buffer flush

  • file_extension: as determined by the store_as parameter.

For example, if

  • s3_object_key_format is as default

  • path is "hello"

  • time_slice_format is "%Y%m%d"

  • store_as is "json"

Then, "hello20141111_0.json" would be an example actual S3 path.

This parameter is for advanced users. Most users should NOT modify it. Also, always make sure that %{index} appears in the customized `s3_object_key_format` (Otherwise, multiple buffer flushes within the same time slice throws an error).


Uses UTC for path formatting. The default format is localtime.


The compression type. The default is "gzip", but you can also choose "lzo", "json", or "txt".


The proxy url. The default is nil.


Verify SSL certificate of the endpoint. The default is true. Set false when you want to ignore the endpoint SSL certificate.

Time Sliced Output Parameters

For advanced usage, you can tune Fluentd's internal buffering mechanism with these parameters.


The time format used as part of the file name. The following characters are replaced with actual values when the file is created:

  • \%Y: year including the century (at least 4 digits)

  • \%m: month of the year (01..12)

  • \%d: Day of the month (01..31)

  • \%H: Hour of the day, 24-hour clock (00..23)

  • \%M: Minute of the hour (00..59)

  • \%S: Second of the minute (00..60)

The default format is %Y%m%d%H, which creates one file per hour.


The amount of time Fluentd will wait for old logs to arrive. This is used to account for delays in logs arriving to your Fluentd node. The default wait time is 10 minutes ('10m'), where Fluentd will wait until 10 minutes past the hour for any logs that occurred within the past hour.

For example, when splitting files on an hourly basis, a log recorded at 1:59 but arriving at the Fluentd node between 2:00 and 2:10 will be uploaded together with all the other logs from 1:00 to 1:59 in one transaction, avoiding extra overhead. Larger values can be set as needed.


The buffer type is file by default (buf_file). The memory (buf_memory) buffer type can be chosen as well. If you use file buffer type, buffer_path parameter is required.

buffer_queue_limit, buffer_chunk_limit

The length of the chunk queue and the size of each chunk, respectively. Please see the Buffer Plugin Overview article for the basic buffer structure. The default values are 64 and 8m, respectively. The suffixes "k" (KB), "m" (MB), and "g" (GB) can be used for buffer_chunk_limit.


The interval between data flushes. The default is 60s. The suffixes "s" (seconds), "m" (minutes), and "h" (hours) can be used.


If set to true, Fluentd waits for the buffer to flush at shutdown. By default, it is set to true for Memory Buffer and false for File Buffer.

retry_wait, max_retry_wait

The initial and maximum intervals between write retries. The default values are 1.0 and unset (no limit). The interval doubles (with +/-12.5% randomness) every retry until max_retry_wait is reached.

Since td-agent will retry 17 times before giving up by default (see the retry_limit parameter for details), the sleep interval can be up to approximately 131072 seconds (roughly 36 hours) in the default configurations.

retry_limit, disable_retry_limit

The limit on the number of retries before buffered data is discarded, and an option to disable that limit (if true, the value of retry_limit is ignored and there is no limit). The default values are 17 and false (not disabled). If the limit is reached, buffered data is discarded and the retry interval is reset to its initial value (retry_wait).


The number of threads to flush the buffer. This option can be used to parallelize writes into the output(s) designated by the output plugin. The default is 1.


Same as Buffered Output but default value is changed to 40.0 seconds.

log_level option

The log_level option allows the user to set different levels of logging for each plugin. The supported log levels are: fatal, error, warn, info, debug, and trace.

Please see the logging article for further details.

Further Reading

This page doesn't describe all the possible configurations. If you want to know about other configurations, please check the link below.

If this article is incorrect or outdated, or omits critical information, please let us know. Fluentd is a open source project under Cloud Native Computing Foundation (CNCF). All components are available under the Apache 2 License.

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