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Nodes are the primary building blocks in an Aion project. Each node represents a configured runtime participant in your system. A node is not just an implementation class or a single API surface. It combines behavior, environment, identities, and capabilities into something that can participate in a live agent system.

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What a node contains

At a high level, a node brings together:
  • a behavior implementation
  • environment-specific configuration
  • one or more identities
  • a set of enabled capabilities
That combination determines how the node can be addressed and what kinds of work it can perform.

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Capabilities

Capabilities define the kinds of interfaces a node can expose. Depending on the node and its configuration, that may include things like:
  • agent-to-agent communication
  • MCP tools and resources
  • event-driven interfaces
  • distribution or network-specific integrations
Capabilities are important because they tell Aion which surfaces can be published and which roles a node can participate in.

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Nodes can play more than one role

One of the most important things to understand is that a node can play multiple roles. The same node may:
  • act as a public distribution entrypoint
  • participate in a sequence as middleware
  • act as a terminal agent
  • expose a direct daemon agent surface
Those roles are related, but they are not interchangeable.

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Public distribution role

When a node is used as a distribution, it acts as the public-facing integration layer. In that role, it receives requests from an external source, starts the configured sequence, and helps return the response back through that same route. For public agent-to-agent distributions, that surface may publish a public distribution card. That card represents the distribution entrypoint for the whole sequence. For other network types, such as Twitter, the distribution is still a public integration point, but it should not publish a public A2A card just because the node has internal A2A capabilities.

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Daemon role

A node can also act as a daemon agent. In that role, the node is addressed directly through its daemon identity rather than through the public distribution sequence. This is useful when another agent needs to call the node itself for extra context or integration-specific functionality. That direct surface is described by the component agent card, not the distribution’s public distribution card.

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Public distribution cards versus component agent cards

These two concepts should be kept separate:
  • The public distribution card describes a distribution’s public sequence entrypoint.
  • The component agent card describes a node’s direct singular-agent surface.
A node may support both, only one, or neither, depending on how it is configured.

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Identities

Because nodes can expose different surfaces, identities matter. In practice, you will often see two different identity concepts around the same node:
  • a distribution-facing identity for the public entrypoint
  • a daemon identity for direct singular-agent access
Those identities are how Aion keeps public routing concerns separate from direct internal agent invocation.

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How to think about nodes

A good mental model is:
  • the node is the configured runtime participant
  • the distribution role is how it participates in public ingress and sequence routing
  • the daemon role is how it exposes itself directly as an agent
That distinction becomes especially important for agent-to-agent capability, because a node may be part of a public sequence and also be directly addressable by other agents.

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Learn more

The rest of the Core Concepts section expands the individual pieces: