Node-RED Concepts

Nodes are triggered by either receiving a message from the previous node in a flow, or by waiting for some external event, such as an incoming HTTP request, a timer or GPIO hardware change. They process that message, or event, and then may send a message to the next nodes in the flow.

A node can have at most one input port and as many output ports as it requires.

• Working with Nodes
• The Core Nodes
• Creating Nodes

For example, the MQTT In and Out nodes use an MQTT Broker config node to represent a shared connection to an MQTT broker.

Config nodes do not appear in the main workspace, but can be seen by opening the Configuration nodes sidebar.

• Working with Configuration nodes
• Configuration node sidebar

The term “flow” is also used to informally describe a single set of connected nodes. So a flow (tab) can contain multiple flows (sets of connected nodes).

• Working with Flows

There are three types of context;

• Node - only visible to the node that set the value
• Flow - visible to all nodes on the same flow (or tab in the editor)
• Global - visible to all nodes

By default, Node-RED uses an in-memory Context store so values do not get saved across restarts. It can be configured to use a file-system based store to make the values persistent. It is also possible to plug-in alternative storage plugins.

• Working with context
• Context Store API

By convention, they have a payload property containing the most useful information.

• Working with messages

They can be used to reduce some visual complexity of a flow, or to package up a group of nodes as a reusable component used in multiple places.

• Working with Subflows

• Working with Wires

Extra nodes can be installed into the palette using either the command-line or the Palette Manager.

• Working with the Palette
• Adding nodes to the palette
• The Palette Manager

The workspace has a row of tabs along the top; one for each flow and any subflows that have been opened.

• Working with the Workspace

• Working with the Sidebar