What is Assembly Replay?
Transloadit Assembly Replay re-executes an Assembly as a new run when its input files can be recovered, without uploading the original files again. It can be triggered manually, and crashed Assemblies are replayed automatically when the Workspace has enabled that option.
How Assembly Replay works
Replay creates another processing attempt from a previous execution. It reuses the Instructions stored with the original Assembly, so a Template is not required, although Template-backed Assemblies can re-resolve their Template at replay time. Inputs are recovered rather than re-transferred: Transloadit prefers its internal temporary copies of uploads, which are retained for roughly 24 hours, and otherwise imports each upload from its stored URL, while Steps that import or generate files simply recreate their inputs. Automatic replay addresses crashed executions in Workspaces that enable it, and manual replay gives an operator explicit retry control. The new run is a distinct execution whose status links back to the parent.
Key facts
- 1Eligibility depends on recoverable inputs, not on a Template or a fixed deadline. An Assembly with neither recoverable uploaded files nor import Steps is rejected with ASSEMBLY_CANNOT_BE_REPLAYED. The roughly 24-hour retention applies to Transloadit’s internal temporary upload copies; it is not a hard replay cutoff.
- 2The replayed work is a new Assembly with its own identifier; its status references the original through parent_assembly_status, and the replay request may supply a different notify_url or override Steps.
- 3External inputs or destinations can change between attempts, making replay non-deterministic when a Step reads mutable remote state or writes to a non-idempotent target.
When Assembly Replay matters
Replay an eligible Assembly when processing failed but re-uploading the originals would be wasteful. Check that every input is still recoverable and that the Instructions still fit the current external state, and track the replay as a new Assembly correlated with its parent.
Common use cases for platform workflows
These examples cover platform workflows broadly, not specifically Assembly Replay.
- Running repeatable upload, import, processing, AI, storage, and notification pipelines.
- Tracking long-running media work independently from an application request.
- Referencing centrally stored credentials by name instead of sending storage secrets with each request.
Working with platform workflows
This guidance covers platform workflows broadly, not just Assembly Replay.
A client authenticates and submits files or references together with workflow instructions. The platform validates the request, schedules dependent operations, records state transitions, and exposes results through a response, polling endpoint, or notification.
Platform concepts become reliable only when their lifecycle is explicit. Authentication, idempotency, retries, timeouts, observability, quotas, and terminal states should be designed together rather than added after failures occur.
What you gain
- Reusable workflows separate application intent from processing infrastructure.
- Stable job identifiers and lifecycle events improve observability and recovery.
- Managed queues and workers let products scale without embedding every media tool.
What it costs
- Synchronous responses are simple but keep connections open while long work executes.
- Aggressive retries improve recovery from transient faults but can duplicate work or overload a dependency.
- Higher concurrency reduces queue time until resource contention or a downstream limit becomes the bottleneck.
Before production
- 1Define authentication, authorization, idempotency, retries, and terminal error behavior.
- 2Observe queue time, execution time, callbacks, and partial results with stable identifiers.
- 3Exercise malformed, duplicate, interrupted, and unauthorized requests before launch.