AWS Lambda for .NET Files

Release 2026-09-08

Amazon.Lambda.DurableExecution (2.0.0)

• Behavior change: steps and child contexts now round-trip their result through the configured serializer on a fresh (non-replay) success, deserializing the just-written checkpoint before returning — matching replay semantics. A custom per-operation serializer's transform is now reflected in the operation result on the first execution, not only on replay. The returned value is a fresh deserialized instance rather than the exact object the step/child body produced. Overflow (replay-children) results are unaffected.
• Behavior change: when a step's fresh-success serializer round-trip fails (e.g. an asymmetric/broken StepConfig.Serializer that cannot deserialize its own output), the step now fails TERMINALLY (FAIL checkpoint + StepException) instead of being routed through the configured RetryStrategy. Previously a non-null RetryStrategy would re-invoke the already-succeeded, side-effecting step body on each attempt (duplicating side effects) until attempts exhausted. This mirrors ChildContextOperation's terminal handling of a round-trip failure.
• Add FileSystemSerializer for offloading large durable operation results to a filesystem (e.g. EFS/S3 Files), keeping only a small pointer in the checkpoint. It wraps an inner ILambdaSerializer, so callers control the on-the-wire format (JSON, compressed, etc.). Introduces the optional IDurableResultSerializer interface and DurableSerializationContext (EntityId + DurableExecutionArn); when an operation's configured serializer implements it, the durable runtime supplies operation/execution identity so external storage can be keyed safely. Applied to Step, ChildContext, WaitForCondition, and Map/Parallel per-item results. Plain ILambdaSerializer serializers are unaffected.
• Add optional per-item serializer override (ItemSerializer) on MapConfig and ParallelConfig; when null the globally-registered ILambdaSerializer is used for item/branch results.
• Add optional per-operation serializer override (Serializer) on StepConfig, CallbackConfig, InvokeConfig, WaitForConditionConfig, and ChildContextConfig; when null the globally-registered ILambdaSerializer is used.
• Behavior change: when a step post-round-trip SUCCEED-checkpoint enqueue fails (e.g. a broken CheckpointBatcher), the failure is now routed through the terminal path (FAIL checkpoint plus StepException) rather than propagating raw, consistent with the fresh-success round-trip failure handling. The side-effecting body is never re-invoked, and if emitting the terminal FAIL itself throws, the error propagates without recursion.
• Behavior change: under NestingType.Flat, Map and Parallel per-item/branch results are now round-tripped through the configured ItemSerializer on a fresh (non-replay) success -- deserializing the just-serialized inline payload before it enters the result -- matching what replay reconstructs from that payload. A non-round-tripping ItemSerializer transform is now reflected in the item/branch result on the first execution, not only on replay, eliminating a fresh-vs-replay divergence. As with steps and child contexts, the returned value is a fresh deserialized instance, and overflow (replay-children) results are unaffected (recovered by re-running the body).
• Behavior change: a fresh-success serializer round-trip DESERIALIZE failure is now terminal on the child-context and Flat Map/Parallel paths, matching StepOperation. (Child) ChildContextOperation now emits a CONTEXT FAIL for a non-virtual, non-suppressed child whose round-trip deserialize throws, instead of throwing with no terminal checkpoint (which left the child STARTED and re-ran its side-effecting body on replay). (Flat Map/Parallel) a per-item round-trip deserialize failure now records that unit's terminal Error inline and still emits the parent SUCCEED, instead of propagating raw with no parent checkpoint (which re-ran every virtual unit body on replay, a poison loop, and bypassed the record-failure contract). Replay reconstructs the terminal failure without re-running or re-deserializing.
• Behavior change (Map/Parallel, NestingType.Nested default): the parent now inlines each Nested unit's ORIGINAL child SUCCEED-checkpoint payload (S(body)) verbatim on the parent summary, and reconstructs it on replay with the child's own operation id, instead of re-serializing the already-round-tripped return value at the parent's per-unit id. This removes a fresh-vs-replay divergence with a non-round-tripping ItemSerializer (fresh vs replay values now match) and, for a context-aware serializer such as FileSystemSerializer, stops the parent writing a second file that orphaned the child's file. Round-tripping (symmetric) serializers and the default JSON serializer are unaffected; the Flat path is unchanged.