FlowFuse Project Nodes

Node-RED instances running within FlowFuse include a set of nodes that make it very quick and easy to securely send and receive messages between different instances in a team.

The nodes act in a similar way to the Node-RED Link nodes, but by allowing the links to extend between different instances, they open up a wide range of possibilities. Remote instances can take part too.

For example, a single Node-RED instance may contain a set of utility flows that you want to reuse in other instances. Rather than copy the flows around, the Project Nodes allow you to easily call those flows and get the result back. The flows stay in one place, so a change to them applies to every caller at once, with the trade-offs covered in Limitations.

The project nodes are included in every FlowFuse product: Edge, Hub and Fleet.

Nodes

There are three nodes in this collection:

• Project In - listens for messages being broadcast by other Node-RED instances, or for messages being sent just to this instance
• Project Out - sends messages to other Node-RED instances
• Project Call - sends messages to other Node-RED instances and waits for a response

The nodes send the whole msg object. Due to the way the nodes encode messages, there are some data types that do not get sent. For example, the msg.req/msg.res properties used by the core HTTP nodes will not be sent. Instead, they are temporarily removed from the message and re-attached when the message is received back.

Each node is configured with a topic on which it either sends or receives messages on. This is similar in concept to MQTT topics - although the nodes do not currently support using MQTT wildcards in their topics.

The Project Out nodes can either broadcast messages on a topic to anyone listening, or they can send messages on a topic to a specific other instance.

The Project In nodes do the opposite - they can either listen for messages being broadcast, or for messages sent directly to them.

The Project Call node can be used to send a message to another Project In node and then wait for a response, with a built-in timeout if it doesn't arrive. The response is sent back using a Project Out node configured to respond to the call node.

Applications

The application features need FlowFuse v3.3 or later (already available on FlowFuse Cloud) and @flowfuse/nr-project-nodes v0.8.0 or later on every instance that uses them, remote instances included. Older versions of the nodes keep working with team broadcasts and hosted instance targets.

The list of targets and sources offered by the nodes is grouped by application. Use the Application filter above the list to show a single application. The list contains the hosted instances in your team and the remote instances assigned to an application. Project Out and Project Call can target either.

Broadcast messages are sent on one of two channels. Choose the channel with the Channel option on the Project In and Project Out nodes:

• Team - received by any instance or remote instance in the team whose Project In node listens on the Team channel. This is the default.
• Application - only received by instances and remote instances in the same application whose Project In node listens on the Application channel. Instances outside the application cannot send or receive these messages.

The channels are separate. A Project In node listening on the Team channel does not receive Application channel broadcasts, even from an instance in the same application.

Received messages include msg.projectLink.applicationId, the application of the sender, and for broadcasts msg.projectLink.scope, the channel it was sent on.

Limitations

Remote instances assigned to an instance are reached through that instance. They share the identity of the instance they are assigned to, so they are not listed separately. A message or call sent to the instance is also received by its remote instances that are listening on the same topic.

Calls need the target to be up. The Project Call node waits for the default timeout of 30 seconds, then logs an error that can be caught with a Catch node. The target instance must be running and have a Project In node listening on the same topic. Because every call travels through the platform's broker, logic called this way is unavailable to a caller whose connection to the platform is down.

Load is shared only in HA mode. The instance holding the called flows serves every caller from a single Node-RED runtime. In High Availability mode the nodes automatically switch to MQTT shared subscriptions, so calls are distributed between the copies.

GitHub

The nodes are published under an Apache-2.0 license and available on GitHub.