MQTT Bridge Connector

MQTT Bridge Overview

The MQTT_BRIDGE connector connects your Coreflux broker to another MQTT broker and keeps selected topics in sync between them. Use it for edge-to-cloud synchronization, linking multiple sites, or mirroring data to a backup broker.

Like call forwarding for messages. You decide which topics get forwarded and in which direction, and the bridge relays every matching message between the two brokers automatically.

When to use it

Push local sensor data from an edge device up to a cloud broker.
Pull commands or configuration from a central broker down to remote sites.
Keep two brokers continuously in sync for redundancy.

Let’s look at how to define a bridge, starting with the most common scenarios.

Quick Start

Edge to cloud (out)
Cloud to edge (in)
Bidirectional (both)

Forward local sensor data up to a cloud broker over TLS:

DEFINE CONNECTOR EdgeToCloud WITH TYPE MQTT_BRIDGE
    ADD SOURCE_CONFIG
        WITH BROKER SELF
    ADD DESTINATION_CONFIG
        WITH BROKER_ADDRESS "iot.cloud-provider.com"
        WITH BROKER_PORT '8883'
        WITH CLIENT_ID "EdgeDevice001"
        WITH USERNAME "edge_user"
        WITH PASSWORD "secure_password"
        WITH USE_TLS "true"
    ADD MAPPING sensorData
        WITH SOURCE_TOPIC "sensors/+/data"
        WITH DESTINATION_TOPIC "edge-001/sensors/+/data"
        WITH DIRECTION "out"

Pull commands from a cloud broker down to the local broker:

DEFINE CONNECTOR CloudCommands WITH TYPE MQTT_BRIDGE
    ADD SOURCE_CONFIG
        WITH BROKER SELF
    ADD DESTINATION_CONFIG
        WITH BROKER_ADDRESS "iot.cloud-provider.com"
        WITH BROKER_PORT '8883'
        WITH CLIENT_ID "EdgeDevice001-Commands"
        WITH USE_TLS "true"
    ADD MAPPING commands
        WITH SOURCE_TOPIC "local/commands/#"
        WITH DESTINATION_TOPIC "edge-001/commands/#"
        WITH DIRECTION "in"

Keep two brokers fully in sync in both directions:

DEFINE CONNECTOR FullSync WITH TYPE MQTT_BRIDGE
    ADD SOURCE_CONFIG
        WITH BROKER SELF
    ADD DESTINATION_CONFIG
        WITH BROKER_ADDRESS "partner-broker.example.com"
        WITH BROKER_PORT '1883'
        WITH CLIENT_ID "SyncClient"
    ADD MAPPING bidirectionalSync
        WITH SOURCE_TOPIC "shared/data/#"
        WITH DESTINATION_TOPIC "partner/data/#"
        WITH DIRECTION "both"

Connection Configuration

A bridge has two endpoints: a SOURCE_CONFIG (usually your local broker) and a DESTINATION_CONFIG (the remote broker). Use WITH BROKER SELF for the local Coreflux broker, or provide explicit connection details for a remote one.

Broker Settings

string

required

IP address or hostname of the broker. Use SELF for the local broker.

integer

required

MQTT port (typically 1883 for unencrypted, 8883 for TLS).

string

Client identifier for the bridge connection. Optional. When unset, the broker generates one that is unique per host, connector and endpoint (cf-<host>-<connector>-src or cf-<host>-<connector>-dst). Set it when the remote broker expects a specific client ID, and keep it distinct for each connector.

Authentication

string

Authentication username.

string

Authentication password.

TLS/Security

boolean

Enable TLS encryption. Default: false.

boolean

Allow untrusted certificates. Default: false.

string

Path to CA certificate file.

string

Path to client certificate for mTLS.

string

Client certificate password.

Connection Handling

integer

Number of reconnection attempts. Default: 5.

Mapping Configuration

Each ADD MAPPING block defines which topics are bridged and in which direction.

Topic Mapping

string

required

Topic pattern to subscribe to on the source broker. Supports wildcards.

string

required

Topic to publish to on the destination broker.

string

required

Data flow direction: out (source→dest), in (dest→source), or both.

Secure mTLS Bridge

For production links between sites, encrypt both endpoints and authenticate with mutual TLS:

DEFINE CONNECTOR SecureBridge WITH TYPE MQTT_BRIDGE
    ADD SOURCE_CONFIG
        WITH BROKER_ADDRESS "192.168.1.10"
        WITH BROKER_PORT '8883'
        WITH CLIENT_ID "SecureSource"
        WITH USE_TLS "true"
        WITH SERVER_CA_CERT_PATH "/certs/ca.pem"
        WITH CLIENT_CERT_PATH "/certs/client.pem"
        WITH CLIENT_CERT_PASS "cert_password"
    ADD DESTINATION_CONFIG
        WITH BROKER_ADDRESS "secure.cloud.com"
        WITH BROKER_PORT '8883'
        WITH CLIENT_ID "SecureDest"
        WITH USE_TLS "true"
        WITH ALLOW_UNTRUSTED_CERTS "false"
    ADD MAPPING secureMapping
        WITH SOURCE_TOPIC "secure/+/data"
        WITH DESTINATION_TOPIC "cloud/+/data"
        WITH DIRECTION "out"

Best Practices

Use TLS for External Connections

Always enable TLS when connecting to external brokers:

WITH USE_TLS "true"

Unique Client IDs

If you set CLIENT_ID, keep it unique per bridge connection to avoid conflicts. Two connections with the same client ID on one remote broker disconnect each other. Leave it unset to use the generated default.

WITH CLIENT_ID "EdgeDevice001-SensorBridge"

Test with Local Broker First

Use WITH BROKER SELF during development:

ADD SOURCE_CONFIG
    WITH BROKER SELF

Secure Credentials

Store passwords securely and use app-specific passwords where available.

Handle Reconnection

Configure appropriate retry settings:

WITH RECONNECTION_RETRIES '10'

Troubleshooting

Bridge Connection Timeout

Verify IP address and port are correct
Check firewall allows outbound connections on the configured port
Ensure remote broker is running and accessible
Try increasing RECONNECTION_RETRIES

TLS/Certificate Errors

Verify certificate paths are correct
Ensure certificates are valid and not expired
Check certificate chain is complete
For testing, use ALLOW_UNTRUSTED_CERTS "true" (not recommended for production)

Messages Not Bridging

Verify SOURCE_TOPIC and DESTINATION_TOPIC are correct
Check DIRECTION setting matches your expected data flow
If you set CLIENT_ID, ensure it is unique across all connections
Check broker logs for subscription errors

Next Steps

System Connectors

Compare bridging and Sparkplug roles.

Sparkplug B

Publish and consume structured industrial MQTT data.

Quick Start

Coreflux MQTT Broker

LoT Language

Coreflux HUB

VS Code - LoT Notebooks

Coreflux Portal

Using AI with Coreflux

Product Updates

MQTT Bridge Overview

When to use it

Quick Start

Connection Configuration

Mapping Configuration

Secure mTLS Bridge

Best Practices

Troubleshooting

Next Steps

System Connectors

Sparkplug B

​MQTT Bridge Overview

​When to use it

​Quick Start

​Connection Configuration

​Mapping Configuration

​Secure mTLS Bridge

​Best Practices

​Troubleshooting

​Next Steps

System Connectors

Sparkplug B

MQTT Bridge Overview

When to use it

Quick Start

Connection Configuration

Mapping Configuration

Secure mTLS Bridge

Best Practices

Troubleshooting

Next Steps