Service Discovery (nats-micro)

DagNats’s internal control-plane endpoints run as nats-micro services. That means dagnats is discoverable and observable with standard NATS tooling out of the box — no extra wiring — and the console Services page shows live instance/version/health data sourced from the $SRV.* discovery protocol rather than a static registry.

This is purely additive: the request/reply subjects are unchanged, so every existing caller keeps working. Wrapping them in micro.Service only adds the discovery + per-endpoint statistics surface.

The services

Each service reports the build version stamped into the binary (an un-stamped dev build reports 0.0.0-dev).

Inspecting with the nats CLI

# List discoverable dagnats services and their instances
nats micro ls

# Full info for one service (endpoints, subjects, metadata)
nats micro info dagnats-api

# Per-endpoint request/error counts + processing time
nats micro stats dagnats-api

Under the hood these use the reserved $SRV.PING, $SRV.INFO, and $SRV.STATS subjects that micro.Service answers automatically. Discovery is request-many-reply: every running instance responds, so nats micro ls shows the instance count for a horizontally-scaled deployment.

In the console

Console → Services renders a live roster: it issues a bounded $SRV discovery request per page load (a short, bounded timeout so a slow or absent responder can never stall the page) and shows, per service:

• Instances — count of $SRV.PING responders.
• Version — from the ping response.
• Status — online (responding, no errors), degraded (errors reported), unknown (reachable but stats unavailable), or stale (registered but not responding). Anything unbacked is dashed, never fabricated.

The page is a union of the services KV roster and live-discovered services, so dagnats-api and dagnats-trigger appear even though they don’t self-register in the KV bucket.

Notes

• Fan-out preserved. The endpoints run without a micro queue group, matching the pre-micro plain-subscribe behavior — every instance receives each message (no load-balancing was silently introduced).
• Error envelope unchanged. Handlers reply with the same JSON error shape as before (they do not use micro’s Nats-Service-Error headers), so existing request/reply clients parse responses identically.