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Our /s3/store Robot

Export files to Amazon S3

🤖/s3/store exports encoding results to Amazon S3.

If you are new to Amazon S3, see our tutorial on using your own S3 bucket.

The URL to the result file in your S3 bucket will be returned in the Assembly Status JSON. If your S3 bucket has versioning enabled, the version ID of the file will be returned within meta.version_id

Avoid permission errors. By default, acl is set to "public". AWS S3 has a bucket setting called "Block new public ACLs and uploading public objects". Set this to False in your bucket if you intend to leave acl as "public". Otherwise, you’ll receive permission errors in your Assemblies despite your S3 credentials being configured correctly.

Use DNS-compliant bucket names. Your bucket name must be DNS-compliant and must not contain uppercase letters. Any non-alphanumeric characters in the file names will be replaced with an underscore, and spaces will be replaced with dashes. If your existing S3 bucket contains uppercase letters or is otherwise not DNS-compliant, rewrite the result URLs using the Robot’s url_prefix parameter.

Limit access

You will also need to add permissions to your bucket so that Transloadit can access it properly. Here is an example IAM policy that you can use. Following the principle of least privilege, it contains the minimum required permissions to export a file to your S3 bucket using Transloadit. You may require more permissions (especially viewing permissions) depending on your application.

Please change {BUCKET_NAME} in the values for Sid and Resource accordingly. Also, this policy will grant the minimum required permissions to all your users. We advise you to create a separate Amazon IAM user, and use its User ARN (can be found in the "Summary" tab of a user here) for the Principal value. More information about this can be found here.

  "Version": "2012-10-17",
  "Statement": [
      "Sid": "AllowTransloaditToStoreFilesIn{BUCKET_NAME}Bucket",
      "Effect": "Allow",
      "Action": ["s3:GetBucketLocation", "s3:ListBucket", "s3:PutObject", "s3:PutObjectAcl"],
      "Resource": ["arn:aws:s3:::{BUCKET_NAME}", "arn:aws:s3:::{BUCKET_NAME}/*"]

The Sid value is just an identifier for you to recognize the rule later. You can name it anything you like.

The policy needs to be separated into two parts, because the ListBucket action requires permissions on the bucket while the other actions require permissions on the objects in the bucket. When targeting the objects there's a trailing slash and an asterisk in the Resource parameter, whereas when the policy targets the bucket, the slash and the asterisk are omitted.

Please note that if you give the Robot's acl parameter a value of "bucket-default", then you do not need the "s3:PutObjectAcl" permission in your bucket policy.

In order to build proper result URLs we need to know the region in which your S3 bucket resides. For this we require the GetBucketLocation permission. Figuring out your bucket's region this way will also slow down your Assemblies. To make this much faster and to also not require the GetBucketLocation permission, we have added the bucket_region parameter to the /s3/store and /s3/import Robots. We recommend using them at all times.

Please keep in mind that if you use bucket encryption you may also need to add "sts:*" and "kms:*" to the bucket policy. Please read here and here in case you run into trouble with our example bucket policy.

Usage example

Export uploaded files to my_target_folder in an S3 bucket:

  "steps": {
    "exported": {
      "robot": "/s3/store",
      "use": ":original",
      "credentials": "YOUR_AWS_CREDENTIALS",
      "path": "my_target_folder/${unique_prefix}/${file.url_name}"


  • use

    String / Array of Strings / Object required

    Specifies which Step(s) to use as input.

    • You can pick any names for Steps except ":original" (reserved for user uploads handled by Transloadit)

    • You can provide several Steps as input with arrays:

      "use": [

    💡 That’s likely all you need to know about use, but you can view Advanced use cases.

  • credentials


    Please create your associated Template Credentials in your Transloadit account and use the name of your Template Credentials as this parameter's value. They will contain the values for your S3 bucket, Key, Secret and Bucket region.

    While we recommend to use Template Credentials at all times, some use cases demand dynamic credentials for which using Template Credentials is too unwieldy because of their static nature. If you have this requirement, feel free to use the following parameters instead: "bucket", "bucket_region" (for example: "us-east-1" or "eu-west-2"), "key", "secret".

  • path

    String ⋅ default: "${unique_prefix}/${file.url_name}"

    The path at which the file is to be stored. This may include any available Assembly variables. The path must not be a directory.

  • url_prefix

    String ⋅ default: "http://{bucket}.s3.amazonaws.com/"

    The URL prefix used for the returned URL, such as "http://my.cdn.com/some/path/".

  • acl

    String ⋅ default: "public-read"

    The permissions used for this file. This can be "public-read", "public", "private" or "bucket-default".

    Please keep in mind that the default value "public-read" can lead to permission errors due to the "Block all public access" checkbox that is checked by default when creating a new Amazon S3 Bucket in the AWS console.

  • check_integrity

    Boolean ⋅ default: false

    Calculate and submit the file's checksum in order for S3 to verify its integrity after uploading, which can help with occasional file corruption issues.

    Enabling this option adds to the overall execution time, as integrity checking can be CPU intensive, especially for larger files.

  • headers

    Object ⋅ default: { "Content-Type": "${file.mime}" }

    An object containing a list of headers to be set for this file on S3, such as { FileURL: "${file.url_name}" }. This can also include any available Assembly Variables. You can find a list of available headers here.

    Object Metadata can be specified using x-amz-meta-* headers. Note that these headers do not support non-ASCII metadata values.

  • tags

    Object ⋅ default: { }

    A hashmap of x-amz meta tags you can attach to the file during the export.

  • host

    String ⋅ default: "s3.amazonaws.com"

    The host of the storage service used. This only needs to be set when the storage service used is not Amazon S3, but has a compatible API (such as hosteurope.de). The default protocol used is HTTP, for anything else the protocol needs to be explicitly specified. For example, prefix the host with https:// or s3:// to use either respective protocol.

  • no_vhost

    Boolean ⋅ default: false

    Set to true if you use a custom host and run into access denied errors.

  • sign_urls_for


    This parameter provides signed URLs in the result JSON (in the signed_url and signed_ssl_url properties). The number that you set this parameter to is the URL expiry time in seconds. If this parameter is not used, no URL signing is done.

Note: The URLs in the result JSON already point to the file on your target storage platform, so you can just save that URL in your database.


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