service-example

Service Example

Demonstrates the service communication pattern with multiple clients: two clients send structured requests to a single server and receive correlated responses via REQUEST_ID metadata. Each client filters responses by its own tracked request IDs.

Architecture

timer (500ms) --> service-client-1 --> request --> service-server --> response --> service-client-1
timer (700ms) --> service-client-2 --> request -->                --> response --> service-client-2

Both clients use the same binary -- the YAML wires them as separate nodes with different timers. Responses fan out to all clients; each filters by its own tracked REQUEST_ID.

Nodes

service-client-1 / service-client-2 (Rust, same binary) -- Sends requests at 500ms / 700ms intervals containing a StructArray with fields a (sequential counter) and b (counter + 10). Uses node.send_service_request() which automatically generates a REQUEST_ID and embeds it in metadata. Tracks pending requests by ID in a HashMap and matches responses. Logs are prefixed with the node ID (DORA_NODE_ID) to distinguish output.

service-server (Rust) -- Receives requests from both clients (via separate named inputs), extracts fields a and b, computes sum = a + b, and returns a response StructArray with the sum field. Uses node.send_service_response() which propagates the REQUEST_ID from the incoming metadata.

Key Concepts

• Multi-client fan-in/fan-out: multiple clients share one server; responses fan out, clients correlate by ID
• Request ID: unique UUID v7 identifier, generated internally by send_service_request()
• Metadata key: REQUEST_ID automatically managed by helper methods
• Arrow StructArray: typed structured data for request/response payloads
• Same binary, multiple nodes: YAML declares distinct nodes pointing to the same executable

See docs/patterns.md for the full pattern specification.

Run

cargo build -p service-example-client -p service-example-server
dora run dataflow.yml

Or in distributed mode:

dora up
dora start dataflow.yml --attach
# Ctrl+C to detach, then:
dora stop --all && dora down

What This Demonstrates

Feature	Where
Multi-client service pattern	Two clients, one server
send_service_request() / send_service_response()	Client / Server
REQUEST_ID metadata correlation	Automatic via helpers
Arrow StructArray for typed payloads	Both nodes
Pending request tracking	Client HashMap
Same binary, multiple nodes	YAML dataflow