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[ aws . topics ]

AWS CLI S3 Configuration

The aws s3 transfer commands, which include the cp, sync, mv, and rm commands, have additional configuration values you can use to control S3 transfers. This topic guide discusses these parameters as well as best practices and guidelines for setting these values.

Before discussing the specifics of these values, note that these values are entirely optional. You should be able to use the aws s3 transfer commands without having to configure any of these values. These configuration values are provided in the case where you need to modify one of these values, either for performance reasons or to account for the specific environment where these aws s3 commands are being run.

Configuration Values

These are the configuration values you can set specifically for the aws s3 command set:

  • max_concurrent_requests - The maximum number of concurrent requests.
  • max_queue_size - The maximum number of tasks in the task queue.
  • multipart_threshold - The size threshold the CLI uses for multipart transfers of individual files.
  • multipart_chunksize - When using multipart transfers, this is the chunk size that the CLI uses for multipart transfers of individual files.
  • max_bandwidth - The maximum bandwidth that will be consumed for uploading and downloading data to and from Amazon S3.

These are the configuration values that can be set for both aws s3 and aws s3api:

  • use_accelerate_endpoint - Use the Amazon S3 Accelerate endpoint for all s3 and s3api commands. You must first enable S3 Accelerate on your bucket before attempting to use the endpoint. This is mutually exclusive with the use_dualstack_endpoint option.
  • use_dualstack_endpoint - Use the Amazon S3 dual IPv4 / IPv6 endpoint for all s3 `` and ``s3api commands. This is mutually exclusive with the use_accelerate_endpoint option.
  • addressing_style - Specifies which addressing style to use. This controls if the bucket name is in the hostname or part of the URL. Value values are: path, virtual, and auto. The default value is auto.
  • payload_signing_enabled - Refers to whether or not to SHA256 sign sigv4 payloads. By default, this is disabled for streaming uploads (UploadPart and PutObject) when using https.

These values must be set under the top level s3 key in the AWS Config File, which has a default location of ~/.aws/config. Below is an example configuration:

[profile development]
s3 =
  max_concurrent_requests = 20
  max_queue_size = 10000
  multipart_threshold = 64MB
  multipart_chunksize = 16MB
  max_bandwidth = 50MB/s
  use_accelerate_endpoint = true
  addressing_style = path

Note that all the S3 configuration values are indented and nested under the top level s3 key.

You can also set these values programmatically using the aws configure set command. For example, to set the above values for the default profile, you could instead run these commands:

$ aws configure set default.s3.max_concurrent_requests 20
$ aws configure set default.s3.max_queue_size 10000
$ aws configure set default.s3.multipart_threshold 64MB
$ aws configure set default.s3.multipart_chunksize 16MB
$ aws configure set default.s3.max_bandwidth 50MB/s
$ aws configure set default.s3.use_accelerate_endpoint true
$ aws configure set default.s3.addressing_style path

To programmatically set these values for a profile other than the default profile the --profile flag can be provided. For example, to set configuration for a profile named test-profile you could run a command like this one:

$ aws configure set s3.max_concurrent_requests 20 --profile test-profile


Default - 10

The aws s3 transfer commands are multithreaded. At any given time, multiple requests to Amazon S3 are in flight. For example, if you are uploading a directory via aws s3 cp localdir s3://bucket/ --recursive, the AWS CLI could be uploading the local files localdir/file1, localdir/file2, and localdir/file3 in parallel. The max_concurrent_requests specifies the maximum number of transfer commands that are allowed at any given time.

You may need to change this value for a few reasons:

  • Decreasing this value - On some environments, the default of 10 concurrent requests can overwhelm a system. This may cause connection timeouts or slow the responsiveness of the system. Lowering this value will make the S3 transfer commands less resource intensive. The tradeoff is that S3 transfers may take longer to complete. Lowering this value may be necessary if using a tool such as trickle to limit bandwidth.
  • Increasing this value - In some scenarios, you may want the S3 transfers to complete as quickly as possible, using as much network bandwidth as necessary. In this scenario, the default number of concurrent requests may not be sufficient to utilize all the network bandwidth available. Increasing this value may improve the time it takes to complete an S3 transfer.


Default - 1000

The AWS CLI internally uses a producer consumer model, where we queue up S3 tasks that are then executed by consumers, which in this case utilize a bound thread pool, controlled by max_concurrent_requests. A task generally maps to a single S3 operation. For example, as task could be a PutObjectTask, or a GetObjectTask, or an UploadPartTask. The enqueuing rate can be much faster than the rate at which consumers are executing tasks. To avoid unbounded growth, the task queue size is capped to a specific size. This configuration value changes the value of that maximum number.

You generally will not need to change this value. This value also corresponds to the number of tasks we are aware of that need to be executed. This means that by default we can only see 1000 tasks ahead. Until the S3 command knows the total number of tasks executed, the progress line will show a total of .... Increasing this value means that we will be able to more quickly know the total number of tasks needed, assuming that the enqueuing rate is quicker than the rate of task consumption. The tradeoff is that a larger max queue size will require more memory.


Default - 8MB

When uploading, downloading, or copying a file, the S3 commands will switch to multipart operations if the file reaches a given size threshold. The multipart_threshold controls this value. You can specify this value in one of two ways:

  • The file size in bytes. For example, 1048576.
  • The file size with a size suffix. You can use KB, MB, GB, TB. For example: 10MB, 1GB. Note that S3 imposes constraints on valid values that can be used for multipart operations.


Default - 8MB

Minimum For Uploads - 5MB

Once the S3 commands have decided to use multipart operations, the file is divided into chunks. This configuration option specifies what the chunk size (also referred to as the part size) should be. This value can specified using the same semantics as multipart_threshold, that is either as the number of bytes as an integer, or using a size suffix.


Default - None

This controls the maximum bandwidth that the S3 commands will utilize when streaming content data to and from S3. Thus, this value only applies for uploads and downloads. It does not apply to copies nor deletes because those data transfers take place server side. The value is in terms of bytes per second. The value can be specified as:

  • An integer. For example, 1048576 would set the maximum bandwidth usage to 1 MB per second.
  • A rate suffix. You can specify rate suffixes using: KB/s, MB/s, GB/s, etc. For example: 300KB/s, 10MB/s.

In general, it is recommended to first use max_concurrent_requests to lower transfers to the desired bandwidth consumption. The max_bandwidth setting should then be used to further limit bandwidth consumption if setting max_concurrent_requests is unable to lower bandwidth consumption to the desired rate. This is recommended because max_concurrent_requests controls how many threads are currently running. So if a high max_concurrent_requests value is set and a low max_bandwidth value is set, it may result in threads having to wait unnecessarily which can lead to excess resource consumption and connection timeouts.


Default - false

If set to true, will direct all Amazon S3 requests to the S3 Accelerate endpoint: To use this endpoint, your bucket must be enabled to use S3 Accelerate. All request will be sent using the virtual style of bucket addressing: Any ListBuckets, CreateBucket, and DeleteBucket requests will not be sent to the Accelerate endpoint as the endpoint does not support those operations. This behavior can also be set if --endpoint-url parameter is set to or for any s3 or s3api command. This option is mutually exclusive with the use_dualstack_endpoint option.


Default - false

If set to true, will direct all Amazon S3 requests to the dual IPv4 / IPv6 endpoint for the configured region. This option is mutually exclusive with the use_accelerate_endpoint option.


Default - auto

There's two styles of constructing an S3 endpoint. The first is with the bucket included as part of the hostname. This corresponds to the addressing style of virtual. The second is with the bucket included as part of the path of the URI, corresponding to the addressing style of path. The default value in the CLI is to use auto, which will attempt to use virtual where possible, but will fall back to path style if necessary. For example, if your bucket name is not DNS compatible, the bucket name cannot be part of the hostname and must be in the path. With auto, the CLI will detect this condition and automatically switch to path style for you. If you set the addressing style to path, you must ensure that the AWS region you configured in the AWS CLI matches the same region of your bucket.


If set to true, s3 payloads will receive additional content validation in the form of a SHA256 checksum which will be calculated for you and included in the request signature. If set to false, the checksum will not be calculated. Disabling this can be useful to save the performance overhead that the checksum calculation would otherwise cause.

By default, this is disabled for streaming uploads (UploadPart and PutObject), but only if a ContentMD5 is present (it is generated by default) and the endpoint uses HTTPS.