Understand custom prefixes for Amazon S3 objects

Objects delivered to Amazon S3 follow the name format of <evaluated prefix><suffix>. You can specify your custom prefix that includes expressions that are evaluated at runtime. Custom prefix you specify will override the default prefix of yyyy/MM/dd/HH.

You can use expressions of the following forms in your custom prefix: !{namespace:value}, where namespace can be one of the following, as explained in the following sections.

• firehose

• timestamp

• partitionKeyFromQuery

• partitionKeyFromLambda

If a prefix ends with a slash, it appears as a folder in the Amazon S3 bucket. For more information, see Amazon S3 Object Name Format in the Amazon Data FirehoseDeveloper Guide.

timestamp namespace

Valid values for this namespace are strings that are valid Java DateTimeFormatter strings. As an example, in the year 2018, the expression !{timestamp:yyyy} evaluates to 2018.

When evaluating timestamps, Firehose uses the approximate arrival timestamp of the oldest record that's contained in the Amazon S3 object being written.

By default, timestamp is in UTC. But, you can specify a time zone that you prefer. For example, you can configure the time zone to Asia/Tokyo in the AWS Management Console or in API parameter setting (CustomTimeZone) if you want to use Japan Standard Time instead of UTC. To see the list of supported time zones, see Amazon S3 Object Name Format.

If you use the timestamp namespace more than once in the same prefix expression, every instance evaluates to the same instant in time.

firehose namespace

There are two values that you can use with this namespace: error-output-type and random-string. The following table explains how to use them.

The firehose namespace values

Conversion	Description	Example input	Example output	Notes
error-output-type	Evaluates to one of the following strings, depending on the configuration of your Firehose stream, and the reason of failure: {processing-failed, AmazonOpenSearchService-failed, splunk-failed, format-conversion-failed, http-endpoint-failed}. If you use it more than once in the same expression, every instance evaluates to the same error string..	myPrefix/result=!{firehose:error-output-type}/!{timestamp:yyyy/MM/dd}	myPrefix/result=processing-failed/2018/08/03	The error-output-type value can only be used in the ErrorOutputPrefix field.
random-string	Evaluates to a random string of 11 characters. If you use it more than once in the same expression, every instance evaluates to a new random string.	myPrefix/!{firehose:random-string}/	myPrefix/046b6c7f-0b/	You can use it with both prefix types. You can place it at the beginning of the format string to get a randomized prefix, which is sometimes necessary for attaining extremely high throughput with Amazon S3.

partitionKeyFromLambda and partitionKeyFromQuery namespaces

For dynamic partitioning, you must use the following expression format in your S3 bucket prefix: !{namespace:value}, where namespace can be either partitionKeyFromQuery or partitionKeyFromLambda, or both. If you are using inline parsing to create the partitioning keys for your source data, you must specify an S3 bucket prefix value that consists of expressions specified in the following format: "partitionKeyFromQuery:keyID". If you are using an AWS Lambda function to create partitioning keys for your source data, you must specify an S3 bucket prefix value that consists of expressions specified in the following format: "partitionKeyFromLambda:keyID". For more information, see the "Choose Amazon S3 for Your Destination" in Creating an Amazon Firehose stream.

Semantic rules

The following rules apply to Prefix and ErrorOutputPrefix expressions.

• For the timestamp namespace, any character that isn't in single quotes is evaluated. In other words, any string escaped with single quotes in the value field is taken literally.

• If you specify a prefix that doesn't contain a timestamp namespace expression, Firehose appends the expression !{timestamp:yyyy/MM/dd/HH/}to the value in the Prefix field.

• The sequence !{ can only appear in !{namespace:value} expressions.

• ErrorOutputPrefix can be null only if Prefix contains no expressions. In this case, Prefix evaluates to <specified-prefix>yyyy/MM/DDD/HH/ and ErrorOutputPrefix evaluates to <specified-prefix><error-output-type>yyyy/MM/DDD/HH/. DDD represents the day of the year.

• If you specify an expression for ErrorOutputPrefix, you must include at least one instance of !{firehose:error-output-type}.

• Prefix can't contain !{firehose:error-output-type}.

• Neither Prefix nor ErrorOutputPrefix can be greater than 512 characters after they're evaluated.

• If the destination is Amazon Redshift, Prefix must not contain expressions and ErrorOutputPrefix must be null.

• When the destination is Amazon OpenSearch Service or Splunk, and no ErrorOutputPrefix is specified, Firehose uses the Prefix field for failed records.

• When the destination is Amazon S3, the Prefix and ErrorOutputPrefix in the Amazon S3 destination configuration are used for successful records and failed records, respectively. If you use the AWS CLI or the API, you can use ExtendedS3DestinationConfiguration to specify an Amazon S3 backup configuration with its own Prefix and ErrorOutputPrefix.

• When you use the AWS Management Console and set the destination to Amazon S3, Firehose uses the Prefix and ErrorOutputPrefix in the destination configuration for successful records and failed records, respectively. If you specify a prefix using expressions, you must specify the error prefix including !{firehose:error-output-type}.

• When you use ExtendedS3DestinationConfiguration with the AWS CLI, the API, or AWS CloudFormation, if you specify a S3BackupConfiguration, Firehose doesn't provide a default ErrorOutputPrefix.

• You cannot use partitionKeyFromLambda and partitionKeyFromQuery namespaces when creating ErrorOutputPrefix expressions.

Example prefixes

Prefix and ErrorOutputPrefix examples

Input	Evaluated prefix (at 10:30 AM UTC on Aug 27, 2018)
Prefix: Unspecified ErrorOutputPrefix: myFirehoseFailures/!{firehose:error-output-type}/	Prefix: 2018/08/27/10 ErrorOutputPrefix: myFirehoseFailures/processing-failed/
Prefix: !{timestamp:yyyy/MM/dd} ErrorOutputPrefix: Unspecified	Invalid input: ErrorOutputPrefix can't be null when Prefix contains expressions
Prefix: myFirehose/DeliveredYear=!{timestamp:yyyy}/anyMonth/rand=!{firehose:random-string} ErrorOutputPrefix: myFirehoseFailures/!{firehose:error-output-type}/!{timestamp:yyyy}/anyMonth/!{timestamp:dd}	Prefix: myFirehose/DeliveredYear=2018/anyMonth/rand=5abf82daaa5 ErrorOutputPrefix: myFirehoseFailures/processing-failed/2018/anyMonth/10
Prefix: myPrefix/year=!{timestamp:yyyy}/month=!{timestamp:MM}/day=!{timestamp:dd}/hour=!{timestamp:HH}/ ErrorOutputPrefix: myErrorPrefix/year=!{timestamp:yyyy}/month=!{timestamp:MM}/day=!{timestamp:dd}/hour=!{timestamp:HH}/!{firehose:error-output-type}	Prefix: myPrefix/year=2018/month=07/day=06/hour=23/ ErrorOutputPrefix: myErrorPrefix/year=2018/month=07/day=06/hour=23/processing-failed
Prefix: myFirehosePrefix/ ErrorOutputPrefix: Unspecified	Prefix: myFirehosePrefix/2018/08/27/ ErrorOutputPrefix: myFirehosePrefix/processing-failed/2018/08/27/