DeliveryPolicy Reference
The delivery policy object appears on every edge in a FlowDSL document. It governs how packets travel from the source node to the destination node.
All fields
| Field | Type | Required | Applies to | Description |
|---|---|---|---|---|
mode | string | Yes | All | Delivery mode: direct, ephemeral, checkpoint, durable, stream |
packet | string | No | All | Packet type reference: "PacketName" or "asyncapi#/..." |
retryPolicy | object | No | durable, ephemeral | Retry configuration |
idempotencyKey | string | No | durable | Template for deduplication key |
deadLetterQueue | string | No | durable, ephemeral | Named dead letter queue |
timeout | string (ISO 8601) | No | durable, ephemeral | Delivery timeout |
priority | integer (1–10) | No | durable, ephemeral | Delivery priority |
batchSize | integer | No | checkpoint | Packets to accumulate before checkpoint write |
checkpointInterval | integer | No | checkpoint | Checkpoint every N packets |
topic | string | No | stream | Kafka topic name |
consumerGroup | string | No | stream | Kafka consumer group |
partitionKey | string | No | stream | Template for Kafka partition key |
stream | string | No | ephemeral | Redis stream name |
maxLen | integer | No | ephemeral | Redis stream max length |
Conditional field requirements
| Field | Required for | Notes |
|---|---|---|
mode | All modes | Always required |
topic | stream | Required — Kafka topic |
stream | ephemeral | Required — Redis stream name |
idempotencyKey | — | Strongly recommended for durable with side effects |
batchSize | — | Default 1 for checkpoint |
direct example
delivery:
mode: direct
packet: ParsedEvent
No additional fields are relevant for direct mode. Delivery is in-process and synchronous.
ephemeral example
delivery:
mode: ephemeral
packet: EnrichmentInput
stream: enrichment-queue
maxLen: 200000
retryPolicy:
maxAttempts: 2
backoff: fixed
initialDelay: PT1S
timeout: PT30S
priority: 5
checkpoint example
delivery:
mode: checkpoint
packet: DocumentChunks
batchSize: 50
checkpointInterval: 1000
durable example
delivery:
mode: durable
packet: OrderPayload
idempotencyKey: "{{payload.orderId}}-charge"
deadLetterQueue: payment-failures
timeout: PT60S
retryPolicy:
maxAttempts: 5
backoff: exponential
initialDelay: PT2S
maxDelay: PT120S
jitter: true
retryOn: [TIMEOUT, RATE_LIMITED, TEMPORARY]
priority: 8
stream example
delivery:
mode: stream
packet: OrderProcessed
topic: orders.processed
consumerGroup: fulfillment-workers
partitionKey: "{{payload.customerId}}"
The partitionKey template ensures all events for the same customer are processed in order by the same Kafka partition.
Field details
idempotencyKey
A Go template string evaluated against each packet. The result is stored in MongoDB to prevent duplicate processing.
idempotencyKey: "{{payload.orderId}}-{{operationId}}"
Available template variables:
{{payload.*}}— any field from the packet payload{{operationId}}— the destination node's operationId{{flowId}}— the current flow ID
Must be unique per logical operation. Reusing keys across different operations causes incorrect deduplication.
timeout
ISO 8601 duration. If the node does not acknowledge the packet within this duration, the packet is considered failed and the retry policy is applied.
| Duration | Meaning |
|---|---|
PT30S | 30 seconds |
PT5M | 5 minutes |
PT1H | 1 hour |
priority
Integer 1–10 (10 = highest). Higher priority packets are delivered first when the queue has backlog. Default: 5.
deadLetterQueue
Name of the dead letter collection in MongoDB. Defaults to {flowId}.dead_letters. Use named queues to separate errors by type for different monitoring and recovery workflows.
Next steps
- Delivery Modes concept — behavior and guarantees
- RetryPolicy reference — retry field reference
- Edge reference — the full edge object