mGate

mGate is a lightweight, scalable, and customizable IoT API gateway designed to support seamless communication across multiple protocols. It enables real-time packet manipulation, features pluggable authentication mechanisms, and offers observability for monitoring and troubleshooting. Built for flexibility, mGate can be deployed as a sidecar or standalone service and can also function as a library for easy integration into applications.

The extensible nature of mGate allows developers to customize it to fit various IoT ecosystems, ensuring optimal performance and security.

Key Features

Some of the key features of mGate include multi-protocol support, real-time packet manipulation, pluggable authentication, observability, and scalability, all while being lightweight, customizable, and easily deployable as a sidecar or standalone service.

Multi-Protocol Support

mGate is built to interface with a wide range of IoT protocols, including:

• MQTT
• CoAP
• HTTP
• WebSocket
• Easily extendable to support additional protocols.

On-the-Fly Packet Manipulation

Allows real-time packet transformation and processing. Custom logic or package interceptors can be injected for modifying incoming and outgoing messages.

Authentication and Authorization

Pluggable authentication system supporting different providers like OAuth, JWT, API Keys, and more. Access Control for fine-grained resource authorization. Easily replaceable auth modules for integration with custom or enterprise identity systems.

Observability

Provides real-time metrics for monitoring system health and performance. Offers logging and tracing to facilitate troubleshooting and optimization and options to easily integrate with Prometheus, Grafana, and OpenTelemetry for detailed tracing and visualization.

Scalable Architecture

mGate is designed to scale horizontally, ensuring it can handle high-throughput environments.

Pluggable and Extensible

Core components are modular, making it easy to plug in custom modules or replace existing ones. Extendable to add new IoT protocols, middleware, and features as needed.

Customizable

Highly configurable, allowing adjustment of protocol-specific behaviors, observability, and performance optimizations. Minimal configuration is required for default deployment but supports deep customization.

Lightweight

Built with Go programming language, it's optimized for low resource usage, making it suitable for both high-performance data centers and resource-constrained IoT edge devices.

Deployment Flexibility

Can be deployed as a sidecar to enhance existing microservices or as a standalone service for direct IoT device interaction. Available as a library for integration into existing applications.

Usage

git clone https://github.com/absmach/mgate.git
cd mgate
make
./build/mgate

Architecture

mGate starts protocol servers, offering connections to devices. Upon the connection, it establishes a session with a remote protocol server. It then pipes packets from devices to the protocol server, inspecting or modifying them as they flow through the proxy.

Here is the flow in more detail:

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

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

// Handler is an interface for mGate 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)
}

The Handler interface is inspired by MQTT protocol control packets; if the underlying protocol does not support some of these actions, the implementation can simply omit them. An example of implementation is given here, alongside with it's main() function.

Deployment

To explain the deployment process, an MQTT broker will be used as an example, given that MQTT is one of the most widely used and feature-rich protocols. mGate does not do load balancing - just pure and simple proxying with TLS termination. This is why it should be deployed right in front of its corresponding MQTT broker instance: one mGate for each MQTT broker instance in the MQTT cluster.

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

LB tasks can be offloaded to a standard ingress proxy - for example, NginX.

Example Setup & Testing of mGate

Requirements

• Golang
• Mosquitto MQTT Server
• Mosquitto Publisher and Subscriber Client

Example Setup of mGate

mGate is used to proxy requests to a backend server. For the example setup, we will use Mosquitto server as the backend for MQTT, and MQTT over Websocket and an HTTP echo server for HTTP.

1. Start the Mosquitto MQTT Server with the following command. This bash script will initiate the Mosquitto MQTT server with WebSocket support. The Mosquitto Server will listen for MQTT connections on port 1883 and MQTT over WebSocket connections on port 8000.

   examples/server/mosquitto/server.sh

2. Start the HTTP Echo Server:

   go run examples/server/http-echo/main.go

3. Start the OCSP/CRL Mock responder:

    go run examples/ocsp-crl-responder/main.go

4. Start the example mGate servers for various protocols:

   go run cmd/main.go

   The cmd/main.go Go program initializes mGate servers for the following protocols:

   • mGate server for MQTT protocol without TLS on port 1884
   • mGate server for MQTT protocol with TLS on port 8883
   • mGate server for MQTT protocol with mTLS on port 8884
   • mGate server for MQTT over WebSocket without TLS on port 8083
   • mGate server for MQTT over WebSocket with TLS on port 8084
   • mGate server for MQTT over WebSocket with mTLS on port 8085 with prefix path /mqtt
   • mGate server for HTTP protocol without TLS on port 8086 with prefix path /messages
   • mGate server for HTTP protocol with TLS on port 8087 with prefix path /messages
   • mGate server for HTTP protocol with mTLS on port 8088 with prefix path /messages

Example testing of mGate

Test mGate server for MQTT protocols

Bash scripts available in examples/client/mqtt directory help to test the mGate servers running for MQTT protocols

• Script to test mGate server running at port 1884 for MQTT without TLS

  examples/client/mqtt/without_tls.sh

• Script to test mGate server running at port 8883 for MQTT with TLS

  examples/client/mqtt/with_tls.sh

• Script to test mGate server running at port 8884 for MQTT with mTLS

  examples/client/mqtt/with_mtls.sh

Test mGate server for MQTT over WebSocket protocols

Go programs available in examples/client/websocket/*/main.go directory helps to test the mGate servers running for MQTT over WebSocket protocols

• Go program to test mGate server running at port 8083 for MQTT over WebSocket without TLS

  go run examples/client/websocket/without_tls/main.go

• Go program to test mGate server running at port 8084 for MQTT over WebSocket with TLS

  go run examples/client/websocket/with_tls/main.go

• Go program to test mGate server running at port 8085 for MQTT over Websocket with mTLS

  go run examples/client/websocket/with_mtls/main.go

Test mGate server for HTTP protocols

Bash scripts available in examples/client/http directory help to test the mGate servers running for HTTP protocols

• Script to test mGate server running at port 8086 for HTTP without TLS

  examples/client/http/without_tls.sh

• Script to test mGate server running at port 8087 for HTTP with TLS

  examples/client/http/with_tls.sh

• Script to test mGate server running at port 8088 for HTTP with mTLS

  examples/client/http/with_mtls.sh

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
MGATE_MQTT_WITHOUT_TLS_ADDRESS	MQTT without TLS inbound (IN) connection listening address	:1884
MGATE_MQTT_WITHOUT_TLS_TARGET	MQTT without TLS outbound (OUT) connection address	localhost:1883
MGATE_MQTT_WITH_TLS_ADDRESS	MQTT with TLS inbound (IN) connection listening address	:8883
MGATE_MQTT_WITH_TLS_TARGET	MQTT with TLS outbound (OUT) connection address	localhost:1883
MGATE_MQTT_WITH_TLS_CERT_FILE	MQTT with TLS certificate file path	ssl/certs/server.crt
MGATE_MQTT_WITH_TLS_KEY_FILE	MQTT with TLS key file path	ssl/certs/server.key
MGATE_MQTT_WITH_TLS_SERVER_CA_FILE	MQTT with TLS server CA file path	ssl/certs/ca.crt
MGATE_MQTT_WITH_MTLS_ADDRESS	MQTT with mTLS inbound (IN) connection listening address	:8884
MGATE_MQTT_WITH_MTLS_TARGET	MQTT with mTLS outbound (OUT) connection address	localhost:1883
MGATE_MQTT_WITH_MTLS_CERT_FILE	MQTT with mTLS certificate file path	ssl/certs/server.crt
MGATE_MQTT_WITH_MTLS_KEY_FILE	MQTT with mTLS key file path	ssl/certs/server.key
MGATE_MQTT_WITH_MTLS_SERVER_CA_FILE	MQTT with mTLS server CA file path	ssl/certs/ca.crt
MGATE_MQTT_WITH_MTLS_CLIENT_CA_FILE	MQTT with mTLS client CA file path	ssl/certs/ca.crt
MGATE_MQTT_WITH_MTLS_CERT_VERIFICATION_METHODS	MQTT with mTLS certificate verification methods, if no value or unset then mGate server will not do client validation	ocsp
MGATE_MQTT_WITH_MTLS_OCSP_RESPONDER_URL	MQTT with mTLS OCSP responder URL, it is used if OCSP responder URL is not available in client certificate AIA	http://localhost:8080/ocsp
MGATE_MQTT_WS_WITHOUT_TLS_ADDRESS	MQTT over Websocket without TLS inbound (IN) connection listening address	:8083
MGATE_MQTT_WS_WITHOUT_TLS_TARGET	MQTT over Websocket without TLS outbound (OUT) connection address	ws://localhost:8000/
MGATE_MQTT_WS_WITH_TLS_ADDRESS	MQTT over Websocket with TLS inbound (IN) connection listening address	:8084
MGATE_MQTT_WS_WITH_TLS_TARGET	MQTT over Websocket with TLS outbound (OUT) connection address	ws://localhost:8000/
MGATE_MQTT_WS_WITH_TLS_CERT_FILE	MQTT over Websocket with TLS certificate file path	ssl/certs/server.crt
MGATE_MQTT_WS_WITH_TLS_KEY_FILE	MQTT over Websocket with TLS key file path	ssl/certs/server.key
MGATE_MQTT_WS_WITH_TLS_SERVER_CA_FILE	MQTT over Websocket with TLS server CA file path	ssl/certs/ca.crt
MGATE_MQTT_WS_WITH_MTLS_ADDRESS	MQTT over Websocket with mTLS inbound (IN) connection listening address	:8085
MGATE_MQTT_WS_WITH_MTLS_PATH_PREFIX	MQTT over Websocket with mTLS inbound (IN) connection path	/mqtt
MGATE_MQTT_WS_WITH_MTLS_TARGET	MQTT over Websocket with mTLS outbound (OUT) connection address	ws://localhost:8000/
MGATE_MQTT_WS_WITH_MTLS_CERT_FILE	MQTT over Websocket with mTLS certificate file path	ssl/certs/server.crt
MGATE_MQTT_WS_WITH_MTLS_KEY_FILE	MQTT over Websocket with mTLS key file path	ssl/certs/server.key
MGATE_MQTT_WS_WITH_MTLS_SERVER_CA_FILE	MQTT over Websocket with mTLS server CA file path	ssl/certs/ca.crt
MGATE_MQTT_WS_WITH_MTLS_CLIENT_CA_FILE	MQTT over Websocket with mTLS client CA file path	ssl/certs/ca.crt
MGATE_MQTT_WS_WITH_MTLS_CERT_VERIFICATION_METHODS	MQTT over Websocket with mTLS certificate verification methods, if no value or unset then mGate server will not do client validation	ocsp
MGATE_MQTT_WS_WITH_MTLS_OCSP_RESPONDER_URL	MQTT over Websocket with mTLS OCSP responder URL, it is used if OCSP responder URL is not available in client certificate AIA	http://localhost:8080/ocsp
MGATE_HTTP_WITHOUT_TLS_ADDRESS	HTTP without TLS inbound (IN) connection listening address	:8086
MGATE_HTTP_WITHOUT_TLS_PATH_PREFIX	HTTP without TLS inbound (IN) connection path	/messages
MGATE_HTTP_WITHOUT_TLS_TARGET	HTTP without TLS outbound (OUT) connection address	http://localhost:8888/
MGATE_HTTP_WITH_TLS_ADDRESS	HTTP with TLS inbound (IN) connection listening address	:8087
MGATE_HTTP_WITH_TLS_PATH_PREFIX	HTTP with TLS inbound (IN) connection path	/messages
MGATE_HTTP_WITH_TLS_TARGET	HTTP with TLS outbound (OUT) connection address	http://localhost:8888/
MGATE_HTTP_WITH_TLS_CERT_FILE	HTTP with TLS certificate file path	ssl/certs/server.crt
MGATE_HTTP_WITH_TLS_KEY_FILE	HTTP with TLS key file path	ssl/certs/server.key
MGATE_HTTP_WITH_TLS_SERVER_CA_FILE	HTTP with TLS server CA file path	ssl/certs/ca.crt
MGATE_HTTP_WITH_MTLS_ADDRESS	HTTP with mTLS inbound (IN) connection listening address	:8088
MGATE_HTTP_WITH_MTLS_PATH_PREFIX	HTTP with mTLS inbound (IN) connection path	/messages
MGATE_HTTP_WITH_MTLS_TARGET	HTTP with mTLS outbound (OUT) connection address	http://localhost:8888/
MGATE_HTTP_WITH_MTLS_CERT_FILE	HTTP with mTLS certificate file path	ssl/certs/server.crt
MGATE_HTTP_WITH_MTLS_KEY_FILE	HTTP with mTLS key file path	ssl/certs/server.key
MGATE_HTTP_WITH_MTLS_SERVER_CA_FILE	HTTP with mTLS server CA file path	ssl/certs/ca.crt
MGATE_HTTP_WITH_MTLS_CLIENT_CA_FILE	HTTP with mTLS client CA file path	ssl/certs/ca.crt
MGATE_HTTP_WITH_MTLS_CERT_VERIFICATION_METHODS	HTTP with mTLS certificate verification methods, if no value or unset then mGate server will not do client validation	ocsp
MGATE_HTTP_WITH_MTLS_OCSP_RESPONDER_URL	HTTP with mTLS OCSP responder URL, it is used if OCSP responder URL is not available in client certificate AIA	http://localhost:8080/ocsp

mGate Configuration Environment Variables

Server Configuration Environment Variables

• ADDRESS : Specifies the address at which mGate will listen. Supports MQTT, MQTT over WebSocket, and HTTP proxy connections.
• PATH_PREFIX : Defines the path prefix when listening for MQTT over WebSocket or HTTP connections.
• TARGET : Specifies the address of the target server, including any prefix path if available. The target server can be an MQTT server, MQTT over WebSocket, or an HTTP server.

TLS Configuration Environment Variables

• CERT_FILE : Path to the TLS certificate file.
• KEY_FILE : Path to the TLS certificate key file.
• SERVER_CA_FILE : Path to the Server CA certificate file.
• CLIENT_CA_FILE : Path to the Client CA certificate file.
• CERT_VERIFICATION_METHODS : Methods for validating certificates. Accepted values are ocsp or crl. For the ocsp value, the tls.Config attempts to retrieve the OCSP responder/server URL from the Authority Information Access (AIA) section of the client certificate. If the client certificate lacks an OCSP responder URL or if an alternative URL is preferred, you can override it using the environmental variable OCSP_RESPONDER_URL.
  For the crl value, the tls.Config attempts to obtain the Certificate Revocation List (CRL) file from the CRL Distribution Point section in the client certificate. If the client certificate lacks a CRL distribution point section, or if you prefer to override it, you can use the environmental variables CRL_DISTRIBUTION_POINTS and CRL_DISTRIBUTION_POINTS_ISSUER_CERT_FILE. If no CRL distribution point server is available, you can specify an offline CRL file using the environmental variables OFFLINE_CRL_FILE and OFFLINE_CRL_ISSUER_CERT_FILE.

OCSP Configuration Environment Variables

• OCSP_DEPTH : Depth of client certificate verification in the OCSP method. The default value is 0, meaning there is no limit, and all certificates are verified.
• OCSP_RESPONDER_URL : Override value for the OCSP responder URL present in the Authority Information Access (AIA) section of the client certificate. If left empty, it expects the OCSP responder URL from the AIA section of the client certificate.

CRL Configuration Environment Variables

• CRL_DEPTH: Depth of client certificate verification in the CRL method. The default value is 1, meaning only the leaf certificate is verified.
• CRL_DISTRIBUTION_POINTS : Override for the CRL Distribution Point value present in the certificate's CRL Distribution Point section.
• CRL_DISTRIBUTION_POINTS_ISSUER_CERT_FILE : Path to the issuer certificate file for verifying the CRL retrieved from CRL_DISTRIBUTION_POINTS.
• OFFLINE_CRL_FILE : Path to the offline CRL file, which can be used if the CRL Distribution point is not available in either the environmental variable or the certificate's CRL Distribution Point section.
• OFFLINE_CRL_ISSUER_CERT_FILE : Location of the issuer certificate file for verifying the offline CRL file specified in OFFLINE_CRL_FILE.

Adding Prefix to Environmental Variables

mGate relies on the caarlos0/env package to load environmental variables into its configuration. You can control how these variables are loaded by passing env.Options to the config.EnvParse function.

To add a prefix to environmental variables, use env.Options{Prefix: "MGATE_"} from the caarlos0/env package. For example:

package main
import (
  "github.com/caarlos0/env/v11"
  "github.com/absmach/mgate"
)

mqttConfig := mgate.Config{}
if err := mqttConfig.EnvParse(env.Options{Prefix:  "MGATE_" }); err != nil {
    panic(err)
}
fmt.Printf("%+v\n")

In the above snippet, mqttConfig.EnvParse expects all environmental variables with the prefix MGATE_. For instance:

• MGATE_ADDRESS
• MGATE_PATH_PREFIX
• MGATE_TARGET
• MGATE_CERT_FILE
• MGATE_KEY_FILE
• MGATE_SERVER_CA_FILE
• MGATE_CLIENT_CA_FILE
• MGATE_CERT_VERIFICATION_METHODS
• MGATE_OCSP_DEPTH
• MGATE_OCSP_RESPONDER_URL
• MGATE_CRL_DEPTH
• MGATE_CRL_DISTRIBUTION_POINTS
• MGATE_CRL_DISTRIBUTION_POINTS_ISSUER_CERT_FILE
• MGATE_OFFLINE_CRL_FILE
• MGATE_OFFLINE_CRL_ISSUER_CERT_FILE

License

Apache-2.0