orbit/agent

The observability agent embeds in every framework process and ships events to a standalone admin server over a single Connect-RPC bidirectional stream. One agent per application node; many agents per server.

Wiring it into an app

The agent owns its configuration type (agent.ExtensionConfig) — the framework carries no admin-specific config. Populate it directly, for example from your own config file, and pass it to agent.NewExtension together with the framework's state directory and your application's version string:

import (
    "context"
    "log"
    "os"

    "github.com/jcsvwinston/nucleus/pkg/app"
    "github.com/jcsvwinston/orbit/agent"
)

func main() {
    cfg, err := app.LoadConfig("nucleus.yml")
    if err != nil {
        log.Fatal(err)
    }
    a, err := app.New(cfg,
        app.WithExtensions(
            agent.NewExtension(agent.ExtensionConfig{
                Endpoints: []string{"https://admin.internal:9090"},
                Token:     os.Getenv("NUCLEUS_ADMIN_TOKEN"),
            }, cfg.StateDir, "v1.2.3"), // your app's version string
        ),
    )
    if err != nil {
        log.Fatal(err)
    }
    if err := a.Run(context.Background()); err != nil {
        log.Fatal(err)
    }
}

Endpoints is the switch. Leave it empty and the extension is a no-op: the framework runs exactly as it would without it. Set it and the agent starts in parallel with the framework's Run, and observability events flow from the framework's pkg/observability bus into the stream.

Node identity

The agent resolves a stable NodeID: a UUIDv4 persisted at ${state_dir}/node_id, falling back to a hostname-derived ephemeral value when the state directory is unavailable.

This is the identity the agent registers under, and the value every fleet view keys on — the Nodes page, per-node stream filters, and the metrics cards. Events shipped over the stream carry the same NodeID, so an event's node_id always matches a registered node. (The agent stamps it over the in-process bus's own node label, which is host-local and does not correlate with the fleet registry.)

Hot-path cost

The agent never blocks the framework's request thread. Every producer-side path — the HTTP middleware, the SQL observer — starts with a single atomic load on observability.Bus.HasSubscribers(kind) and short-circuits when nobody is watching.

What's inside

The agent is layered:

• Node identity — resolution and persistence, as described above.
• Event pipeline — conversion and sampling, then a drop-oldest ring buffer that bridges brief disconnects.
• Transport — an endpoint-failover dialer with exponential backoff, and the bidirectional stream lifecycle: registration, recv/send/heartbeat, and replay on reconnect.
• Metrics — the admin_agent_* Prometheus collectors.
• RBAC snapshot — the read-only handler behind the fleet UI's Access control screen, wired automatically from the application's authorizer when the extension attaches. No extra configuration.

The top-level Agent exposes New, Run, NodeID, Connected, and Metrics.