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Logs

FaaSr logs

Logs produced by FaaSr functions using the faasr_log() API are stored in an S3 server. This document overviews how to select an S3 server to store these logs, and the folder naming structure to help you locate a particular log

Selecting an S3 bucket for logs

  • In the typical scenario, a single S3 server/bucket can be used for both workflow files and logs, but you may also use separate buckets
  • The S3 server used for logs is configured as the Default server to store logs under Workflow settings in the FaaSr Workflow Builder Web UI (this corresponds to the LoggingDataStore field in the workflow JSON)

Log folder naming convention

  • Using the FaaSr Workflow Builder Web UI you must name your workflow uniquely; we'll use WorkflowName in this example
  • Using the FaaSr Workflow Builder Web UI you can also provide a name for the top-level log folder; if you do not provide one, by default the name is set to FaaSrLog
  • Then, the path where you can find logs for a particular Action function execution is:

FaaSrLog/WorkflowName/InvocationTimestamp/InvocationID/ActionName.txt

Where: - ActionName is the name of the action (i.e. the name of a node in your DAG). For actions invoked concurrently with rank, the log file name also includes the rank, e.g. ActionName(Rank).txt - InvocationID is a specific invocation of your Action. Refer to the invocationID documentation for the different types of invocation IDs supported (UUID, user-provided, and timestamp-derived) - InvocationTimestamp is a string-formatted invocation timestamp recorded at the time your workflow's entry action starts execution. It is recorded as an ISO 8601-like timestamp with filename-safe separators

Examples

  • Suppose you run the FaaSr tutorial as an example
  • In this workflow configuration, the log folder is the default FaaSrLog and the workflow name is tutorial
  • Suppose you also leave the InvocationID as default, which generates a unique UUID automatically at the start entry point. In this example, let's assume the UUID generated is: f81d4fae-7dec-11d0-a765-00a0c91e6bf6
  • Suppose when you invoke the workflow, the current time seen by the start action was timestamped as 2025-08-29T23-17-01

You will then be able to retrieve logs for the sum action from the (unique) path:

FaaSrLog/tutorial/2025-08-29T23-17-01/f81d4fae-7dec-11d0-a765-00a0c91e6bf6/sum.txt

If you invoke the workflow again, a new timestamp and UUID will be generated

Cloud logs