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Connect Nodes

Connecting nodes creates the data flow in your graph. This guide shows you how to connect nodes together, creating the pathways that data follows through your pipeline.

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Prerequisites

Before you begin, make sure you have:

Nodes Created

At least two nodes created in your graph with ports configured.

Ports Added

Nodes have input and output ports. See Add Ports if needed.

Compatible Types

Output port type matches input port type. Ports must use the same schema.

Graph Editor Open

Cerulion Graph Editor running with your graph open on the canvas.
Connecting nodes automatically creates topics. You don’t need to create topics manually—the framework handles this for you.

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What You’ll Do

You’ll connect nodes by drawing links from output ports to input ports. Each connection creates a topic that carries data between the nodes.

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Step-by-Step Guide

1

Enter connection mode

Click the Connect tool in the toolbar (or press C key).
The cursor should change to a crosshair or connection icon, indicating connection mode is active.
You can also right-click on an output port and select “Connect to…” from the context menu.
2

Click output port

Click and hold on a green output port (on the right side of a node).
You should see a line starting from the output port, following your cursor as you move the mouse.
The line shows a preview of the connection you’re about to create.
3

Drag to input port

Drag the line to a blue input port (on the left side of another node).
The input port should highlight when you’re hovering over it, indicating it’s a valid connection target.
If the port doesn’t highlight, the types may not match. Check that both ports use the same schema type.
4

Release to connect

Release the mouse button to create the connection.
You should see:
  • A line connecting the two ports
  • A topic automatically created (visible in topics panel)
  • The connection is active and ready to carry data
The topic is automatically named based on the port names. You can rename it later in the properties panel.
5

Verify the connection

Click on the connection line to verify:
  • Topic name appears in the properties panel
  • Topic type matches the port types
  • Connection is valid (no error indicators)
The properties panel should show the topic details, confirming the connection is set up correctly.
6

Connect more nodes (optional)

Repeat steps 2-5 to connect more nodes:
  • Linear chain: Node A → Node B → Node C
  • Fan-out: One output to multiple inputs
  • Fan-in: Multiple outputs to one input
Arrange nodes so connections don’t cross unnecessarily. A clean layout is easier to understand.

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Understanding Connections

After connecting nodes:
  • Topics are created automatically with default names
  • Data can flow from output to input
  • Type safety is enforced - only compatible types can connect
  • Visual representation shows data flow at a glance

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Connection Patterns

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Linear Pipeline

Simple sequential connections: 
Node A → Node B → Node C → Node D
Use when: Data flows through processing stages sequentially.

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Fan-Out (Broadcast)

One output to multiple inputs: 
        → Node B
Node A → → Node C
        → Node D
Use when: Broadcasting data to multiple consumers.

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Fan-In (Merge)

Multiple outputs to one input: 
Node A →
Node B → → Node C
Node D →
Use when: Collecting data from multiple sources (use with caution).

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Manual Topic Creation (Advanced)

Topics are automatically created when you connect nodes. You only need to create them manually for advanced scenarios like pre-configuring topics or setting up complex topologies.
For advanced scenarios, you can create topics manually before connecting nodes:
1

Open topic dialog

Click Topic in the toolbar (or press T key), or right-click on the canvas and select “New Topic”.
The topic creation dialog should open.
2

Enter topic name

Enter a descriptive name for the topic:
  • Use lowercase with underscores (e.g., temperature_readings, sensor_data)
  • Be descriptive and specific
  • Avoid generic names like data or topic1
3

Select schema type

From the type dropdown, select the schema that defines this topic’s data structure. All nodes connecting to this topic must use the same type.
4

Configure transport (optional)

Configure how data is transported:
  • Auto (recommended) - Framework selects local or network automatically
  • Local - Force local shared memory transport
  • Network - Force network transport via Zenoh
5

Save the topic

Click Create to create the topic. The topic will appear in the topics panel and can be connected to nodes.

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Editing Connections

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Renaming Topics

To rename a topic created by a connection:
1

Select the connection

Click on the connection line to select it.
2

Open properties

The properties panel should show the topic properties:
  • Name - Edit the topic name
  • Type - The schema type (read-only)
  • Transport - Local or network (can be changed)
  • QoS Settings - Quality of service configuration (optional)
3

Edit topic name

Change the topic name in the properties panel.
The topic name updates immediately. The new name appears in the topics panel.

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Deleting Connections

To delete a connection:
1

Select the connection

Click on the connection line to select it.
2

Delete

Press Delete key (or right-click → Delete).
Deleting a connection also deletes the associated topic. Make sure no other nodes depend on that topic.
The connection line should disappear, and the topic should be removed.

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Connection Validation

The editor validates connections before creating them:

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Valid Connections

  • Type match - Output type exactly matches input type
  • Same schema - Both ports use the same schema
  • Compatible types - Types are structurally compatible

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Invalid Connections

  • Type mismatch - Output and input types don’t match
  • Self-connection - Trying to connect a node to itself (usually invalid)
  • Duplicate connection - Ports already connected
The editor prevents invalid connections. If you can’t connect two ports, check that their types are compatible.

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Best Practices

Clear Layout

Arrange nodes so connections don’t cross unnecessarily. A clean layout is easier to understand.

Descriptive Names

Rename topics to have meaningful names. “temperature_readings” is better than “topic1”.

Type Safety

Always ensure port types match before connecting. The editor helps, but understanding types prevents errors.

Avoid Loops

Be careful with circular connections. They can cause infinite loops if not handled properly.

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Troubleshooting

Problem: Editor won’t let you create a connection.Solutions:
  • Check that port types match (output type must match input type)
  • Verify both nodes are in the same graph
  • Ensure ports aren’t already connected (delete existing connection first)
  • Check for schema errors that might prevent type validation
  • Verify the connection mode is active (C key or Connect tool)
Problem: Connection is gone after moving nodes or saving.Solutions:
  • Check that both nodes still exist
  • Verify the graph file was saved correctly
  • Look for errors in the console
  • Try recreating the connection
  • Check for validation errors
Problem: Editor shows type mismatch when trying to connect.Solutions:
  • Verify both ports use the same schema
  • Check that schemas are correctly defined
  • Ensure schema files are saved and loaded
  • Look for schema validation errors
  • Try refreshing the project

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Next Steps

Now that you can connect nodes, learn more:

Write Node Code

Learn how to write code that uses these connections.

Generate and Run

Generate code and run your connected graph.

Ports and Links

Understand how ports and links work together.

Topics

Learn how connections automatically create topics.