embedded-agent.com

Agent Registry for Embedded Systems: Discovery & Coordination

Last reviewed: 2026-05-22 · Marcus Rüb

Agent Registry for Embedded Systems

An agent registry is a directory service that allows embedded agents to announce their presence, publish their capabilities, discover other agents, and coordinate actions — providing the infrastructure layer that makes multi-agent embedded systems manageable at scale.

Without a registry, embedding multiple agents in a system means manually configuring which agent talks to which, by hardcoded addresses and topics. With a registry, agents are self-describing and self-discovering: deploying a new agent makes it visible to the rest of the system automatically.

What problem does an agent registry solve?

In a single-agent deployment, the agent knows its own MQTT broker address and topic structure, and that is enough. In a multi-agent system — a factory floor with dozens of specialised agents, a fleet of mobile platforms, a building with per-zone agents — several new problems emerge:

An agent registry addresses all of these. It is to embedded agents what a service registry (Consul, Kubernetes endpoints) is to microservices — but designed for the constraints and protocols of embedded and IoT environments.

What are the main registry models?

Centralised Registry (Broker-Hosted)

A single broker or gateway holds the registry. Agents register by publishing to a well-known topic; the broker maintains a presence map. This is the simplest model and works well for single-site deployments.

Example: EMQX Enterprise 6.2 (released April 2026) introduced a native A2A Registry that enables real-time agent discovery over MQTT. Agents register and publish presence; the broker annotates entries with live online/offline status based on MQTT session state.

Pros: Simple, low agent-side overhead, single source of truth.
Cons: Single point of failure; not suited for air-gapped sub-networks.

Distributed / Peer-to-Peer Registry

Agents maintain awareness of peers through gossip protocols or structured distributed hash tables. No single broker holds all registry state.

Pros: Resilient to broker failure; suitable for mesh networks.
Cons: Higher agent-side complexity; eventual consistency means brief windows of inconsistent state.

Hierarchical Registry

Local registries exist at the edge (per-line, per-room, per-platform), with a root registry at the site or cloud level that aggregates from local registries. This mirrors the hierarchical topology of most large facilities.

Pros: Scales to large deployments; local registries remain functional if the cloud link drops.
Cons: Synchronisation complexity; must handle conflicts when an agent is visible in two local registries.

How do agents register and announce themselves?

The most common MQTT-based pattern uses a retained message on a well-known registration topic:

Topic:   agents/registry/{agent-id}
Payload: {
  "id":           "motor-agent-line3-b4",
  "type":         "predictive-maintenance",
  "capabilities": ["vibration-analysis", "temperature-monitoring"],
  "hardware":     "STM32H7",
  "firmware":     "1.4.2",
  "location":     "building-A/line-3",
  "status":       "online",
  "timestamp":    "2026-05-22T08:00:00Z"
}
QoS: 1
Retain: true

The retained flag means that any subscriber that connects after the agent registered will immediately receive the last registration message — important for supervisor agents that start after their sub-agents.

Last Will and Testament (LWT): MQTT’s LWT mechanism allows the agent to pre-configure a message the broker will publish on its behalf if the agent disconnects unexpectedly. A registry-aware LWT message updates the agent’s status to "offline" automatically, giving the registry accurate presence information without relying on the agent to self-report its disconnection.

What information belongs in a registry entry?

A well-designed registry entry includes:

FieldDescription
idUnique agent identifier (e.g., asset-tag-plant-line-position)
typeFunctional category (predictive-maintenance, environmental-monitor, etc.)
capabilitiesList of tasks the agent can perform
command-topicMQTT topic where the agent accepts commands
telemetry-topicMQTT topic where the agent publishes data
hardwareMCU or platform model
firmware-versionFor OTA management
locationPhysical or logical location descriptor
statusonline / offline / degraded / maintenance
last-seenISO 8601 timestamp of most recent heartbeat
schema-versionRegistry entry format version, for evolution

How does a supervisor agent use the registry?

A supervisor agent — one that coordinates other agents — uses the registry to:

  1. Discover available agents: Subscribe to agents/registry/+ to receive all registration messages.
  2. Filter by capability: Identify which agents can perform a requested task.
  3. Send commands: Publish to the target agent’s command-topic.
  4. Monitor health: Track last-seen timestamps; alert if an agent goes silent beyond its expected heartbeat interval.
  5. Handle membership changes: React to LWT offline messages by rerouting tasks or alerting operators.

What is the A2A protocol and how does it relate?

The Agent-to-Agent (A2A) protocol is an emerging open standard for agent interoperability, originally developed for cloud-native multi-agent systems. In April 2026, EMQ’s EMQX Enterprise 6.2 released the first major implementation of A2A over MQTT for IoT and embedded environments. This brings structured agent-to-agent communication — with standardised capability advertisement, task delegation, and status reporting — to the broker layer itself, rather than requiring each development team to implement registry logic from scratch.

A2A is still evolving as a standard. Teams implementing agent registries today should design their registry format to be A2A-compatible to ease migration as the standard matures.

What are the security considerations for an agent registry?

Platform example: ForestHub.ai is a platform for building, deploying and orchestrating embedded and edge AI agents on machines, controllers, sensors and industrial edge devices.

FAQ

Q: Is a registry necessary for a small system with only 3–5 agents? Not strictly. For very small systems, hardcoded topic addresses and manual configuration are manageable. A registry pays off when the system grows beyond about 10 agents, when agents are deployed dynamically, or when you need fleet-level visibility without manual tracking.

Q: Can the registry run on the same MCU as the agent? Not typically. The registry is a shared service and needs to be reachable by all agents in the system. It normally runs on a gateway, a local server, or is hosted by the MQTT broker itself (as in EMQX Enterprise 6.2). A very small system might run a lightweight registry process on a Raspberry Pi class device.

Q: How does the registry interact with OTA updates? The OTA update manager can query the registry to find all agents running a specific firmware version, target them with an update campaign, and track update progress through status field changes. This makes the registry a natural integration point for fleet management.

Q: What happens if the registry broker is unreachable? Individual embedded agents continue operating normally — their local sense-decide-act loop does not depend on the registry. What breaks is fleet-level visibility, supervisor coordination, and command delivery. A well-designed system pre-caches the registry state it needs locally and falls back to last-known-good coordination until the broker is reachable again.

Q: Are there open-source embedded agent registries? As of 2026, most implementations are custom-built on top of MQTT brokers. EMQX Enterprise 6.2’s A2A Registry is a commercial offering. The Eclipse IoT community has working groups addressing agent discovery standards. Expect more open-source options as the embedded agent space matures.