Spec

Runtime Bindings Reference

The x-runtime extension for binding FlowDSL delivery modes to specific infrastructure.

Runtime bindings allow you to configure delivery mode infrastructure at the edge level — overriding the runtime's defaults for a specific edge. Use them when you need non-default MongoDB collections, Redis streams, or Kafka topics.

`x-runtime` extension

yaml

edges:
  - from: ProcessOrder
    to: NotifyFulfillment
    delivery:
      mode: durable
      packet: OrderProcessed
    x-runtime:
      mongodb:
        collection: orders.fulfillment_queue    # Override default collection name
        writeConcern: majority                   # "majority" or "1"
        readPreference: primaryPreferred

  - from: IngestEvent
    to: ProcessEvent
    delivery:
      mode: ephemeral
      stream: high-priority-events
    x-runtime:
      redis:
        keyPrefix: "flowdsl:hp:"   # Custom key prefix
        maxLen: 1000000
        trimStrategy: maxlen        # "maxlen" or "minid"

  - from: PublishResult
    to: ExternalConsumers
    delivery:
      mode: stream
      topic: results.processed
    x-runtime:
      kafka:
        acks: all                   # "0", "1", or "all"
        compression: lz4            # "none", "gzip", "snappy", "lz4", "zstd"
        batchSize: 16384
        lingerMs: 5

MongoDB binding fields

Field	Type	Default	Description
`collection`	string	`{flowId}.packets`	MongoDB collection name
`writeConcern`	string	`"1"`	`"1"` or `"majority"`
`readPreference`	string	`"primary"`	`"primary"`, `"primaryPreferred"`, `"secondary"`

Redis binding fields

Field	Type	Default	Description
`keyPrefix`	string	`"flowdsl:"`	Prefix for Redis keys
`maxLen`	integer	100000	Maximum stream length
`trimStrategy`	string	`"maxlen"`	`"maxlen"` or `"minid"`

Kafka binding fields

Field	Type	Default	Description
`acks`	string	`"1"`	Producer acknowledgment: `"0"`, `"1"`, or `"all"`
`compression`	string	`"none"`	Compression codec
`batchSize`	integer	16384	Producer batch size in bytes
`lingerMs`	integer	0	Producer linger time in milliseconds

When to use runtime bindings

Most flows do not need x-runtime — the runtime's defaults are appropriate for the vast majority of use cases.

Use x-runtime when:

You need to use a specific MongoDB collection for compliance or monitoring
You need Kafka acks: all for a specific edge that requires stronger durability
You are tuning Kafka producer settings for high-throughput edges
You need to share a Redis stream with non-FlowDSL consumers

Next steps

Extensions reference — all supported extension fields
DeliveryPolicy reference — delivery policy fields
High-Throughput Pipelines — performance tuning

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RetryPolicy Reference

Complete field reference for the RetryPolicy object in FlowDSL.

Tools

Official FlowDSL tools — Studio, CLI, and language SDKs.