mProxy

mProxy is an MQTT proxy.

It is deployed in front of MQTT broker and can be used for authorization, packet inspection and modification, logging and debugging and various other purposes.

Usage

go get github.com/absmach/mproxy
cd $(GOPATH)/github.com/absmach/mproxy
make
./mproxy

Architecture

mProxy starts TCP and WS servers, offering connections to devices. Upon the connection, it establishes a session with a remote MQTT broker. It then pipes packets from devices to MQTT broker, inspecting or modifying them as they flow through proxy.

Here is the flow in more details:

• Device connects to mProxy's TCP server
• mProxy accepts the inbound (IN) connection and estabishes a new session with remote MQTT broker (i.e. it dials out to MQTT broker only once it accepted new connection from a device. This way one device-mProxy connection corresponds to one mProxy-MQTT broker connection.)
• mProxy then spawn 2 goroutines: one that will read incoming packets from device-mProxy socket (INBOUND or UPLINK), inspect them (calling event handlers) and write them to mProxy-broker socket (forwarding them towards the broker) and other that will be reading MQTT broker responses from mProxy-broker socket and writing them towards device, in device-mProxy socket (OUTBOUND or DOWNLINK).

mProxy can parse and understand MQTT packages, and upon their detection it actually calls external event handlers. Event handlers should implement the following interface defined in pkg/mqtt/events.go:

// Handler is an interface for mProxy hooks
type Handler interface {
	// Authorization on client `CONNECT`
	// Each of the params are passed by reference, so that it can be changed
	AuthConnect(ctx context.Context) error

	// Authorization on client `PUBLISH`
	// Topic is passed by reference, so that it can be modified
	AuthPublish(ctx context.Context, topic *string, payload *[]byte) error

	// Authorization on client `SUBSCRIBE`
	// Topics are passed by reference, so that they can be modified
	AuthSubscribe(ctx context.Context, topics *[]string) error

	// After client successfully connected
	Connect(ctx context.Context)

	// After client successfully published
	Publish(ctx context.Context, topic *string, payload *[]byte)

	// After client successfully subscribed
	Subscribe(ctx context.Context, topics *[]string)

	// After client unsubscribed
	Unsubscribe(ctx context.Context, topics *[]string)

	// Disconnect on connection with client lost
	Disconnect(ctx context.Context)
}

An example of implementation is given here, alongside with it's main() function.

Deployment

mProxy does not do load balancing - just pure and simple proxying. This is why it should be deployed right in front of it's corresponding MQTT broker instance: one mProxy for each MQTT broker instance in the MQTT cluster.

Usually this is done by deploying mProxy as a side-car in the same Kubernetes pod alongside with MQTT broker instance (MQTT cluster node).

TLS termination and LB tasks can be offloaded to a standard ingress proxy - for example NginX.

Configuration

The service is configured using the environment variables presented in the following table. Note that any unset variables will be replaced with their default values.

Variable	Description	Default
MPROXY_WS_HOST	WebSocket inbound (IN) connection host	0.0.0.0
MPROXY_WS_PORT	WebSocket inbound (IN) connection port	8080
MPROXY_WS_PATH	WebSocket inbound (IN) connection path	/mqtt
MPROXY_WSS_PORT	WebSocket Secure inbound (IN) connection port	8080
MPROXY_WSS_PATH	WebSocket Secure inbound (IN) connection path	/mqtt
MPROXY_WS_TARGET_SCHEME	WebSocket Target schema	ws
MPROXY_WS_TARGET_HOST	WebSocket Target host	localhost
MPROXY_WS_TARGET_PORT	WebSocket Target port	8888
MPROXY_WS_TARGET_PATH	WebSocket Target path	/mqtt
MPROXY_MQTT_HOST	MQTT inbound connection host	0.0.0.0
MPROXY_MQTT_PORT	MQTT inbound connection port	1883
MPROXY_MQTTS_PORT	MQTTS inbound connection port	8883
MPROXY_MQTT_TARGET_HOST	MQTT broker host	0.0.0.0
MPROXY_MQTT_TARGET_PORT	MQTT broker port	1884
MPROXY_CLIENT_TLS	Flag that indicates if TLS should be turned on	false
MPROXY_CA_CERTS	Path to trusted CAs in PEM format
MPROXY_SERVER_CERT	Path to server certificate in pem format
MPROXY_SERVER_KEY	Path to server key in pem format
MPROXY_LOG_LEVEL	Log level	debug

License

Apache-2.0