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- The repetitive implementation of common functionality like device communication and management is error prone and inefficient regarding costs, development time and runtime resources.
- The tight integration of devices with a specific application de facto partitions the set of things into classes determined by the application the devices have been intially integrated with. This makes it hard to create new cross-domain solutions and business models leveraging devices coming from different application domains.
- The applications implemented this way are often designed to interact with a limited number of devices in an enterprise environment only. Scaling out such applications with an increasing number of devices therefore often requires massive refactoring (if not re-architecting) of the device integration layer in order to support horizontal scalability as required in most cloud-based use cases.
Hono provides a uniform (remote) service interface that supports both the Telemetry as well as Command & Control message exchange pattern requirements.
Connectivity is at the heart of IoT solutions. Devices (things) need to be connected to a back end component where the data and functionality of the devices is leveraged to provide some higher level business value. IoT solution developers can pick from a wide array of existing (open source) technology to implement a device connectivity & management layer for the particular type of devices at hand. While this is often fun for the developers to do, the resulting solutions are often silo applications lacking the ability to scale horizontally with the number of devices connected and the number of back end components consuming the device data and functionality.
The Eclipse IoT Working Group has therefore discussed a more generic, cloud-based IoT platform architecture which better supports the implementation of IoT solutions without requiring developers to solve some of the recurring (technical) challenges over and over again. The diagram below provides an overview of the IoT Server Platform as discussed in the working group.
The diagram shows how devices in the field are connected to a cloud-based back end either via a Field Gateway (e.g. something like Eclipse Kura) or directly to so-called Protocol Adapters. The Protocol Adapters' responsibility is abstracting communication protocols as well as providing location transparency of devices to the other back end components. The devices upload (sensor) data to the back end while the functions/services they expose can be invoked from the back end. These two directions of information flow can be characterized as follows:
Data flowing upstream (left to right) from devices to the back end to a consumer like a Business Application or the Device Management component usually consists of a small set of discrete values like sensor readings or status property values. In most cases these messages are one-way only, i.e. devices sending this kind of data usually do not expect a reply from the back end.
Command & Control
Messages flowing downstream (right to left) from back end components like Business Applications often represent invocations of services or functionality provided by connected devices, e.g. instructions to download and apply a firmware update, setting configuration parameters or querying the current reading of a sensor. In most cases a reply to the sent message is expected by the back end component.
It seems reasonable to assume that the number of messages flowing upstream (Telemetry) will be orders of magnitude larger than the number of messages flowing downstream (Command & Control). The aggregated overall number of messages flowing upstream is expected to be in the range of several hundred thousand to millions per second. Note that in this architecture the same (cloud-based) infrastructure is shared by multiple solutions.
The IoT Connector component provides the central link between the device-facing Protocol Adapters, additional re-usable back end components, e.g. Device Management or Software Provisioning, and last but not least the IoT solutions leveraging the devices' data and services. Solution developers can use the IoT Connector to uniformly and transparently interact with all kinds of devices without the need for caring about the particular communication protocol(s) the devices use. Multiple solutions can use the same IoT Connector instance running in a shared cloud environment in order to share the data and functionality of all connected devices. The IoT Connector ensures that only those components can consume data and control devices that have been granted authorization by the device owner. In this regard the IoT Connector can be considered an IoT specific message broker targeted at cloud deployment scenarios.
The IoT Connector component needs to fulfill a set of non-functional requirements, in particular regarding horizontal scalability, that are specific to both the deployment environment (cloud) and the intended architectural platform characteristics (as opposed to embedding a connectivity layer into applications individually). However, these requirements are not specific to any particular application domain. From a technical point of view it makes no difference if a sensor reading received via a LWM2M protocol adapter represents a temperature or the relative humidity. In both cases the IoT Connector's responsibility is to forward the messages containing the values to (potentially multiple) authorized consumers without introducing too much latency.
Features at a glance
- Secure message dispatching
- Support for different message exchange patterns
- Used for cloud service federation
Provides interfaces to support implementation of protocol adaptors which allow:
- Sending telemetry data
- Receiving device control messages (from applications/solutions)
- Registering authorized consumers of telemetry data received from connected devices
- establishing a connection to a RabbitMQ broker
- managing authorization information per topics
- sending messages
- registering topic based handlers for receiving & processing messages
- storing all information required for authorization
- accepting incoming messages and
- dispatching messages to all authorized consumers
We would like to be able to demonstrate a first PoC (based mostly on the initial contribution code) at EclipseCon 2016 in Reston. A first release should be available by Q3 2016.
As a starting point we provide an implementation based on RabbitMQ because of its easy availability both as a service in existing Cloud Foundry based environments as well as in the form of pre-built Docker images. In order to also provide an implementation supporting horizontal scale-out, we will also create an implementation based on Apache Kafka. Future versions may also support using other cloud-based offerings (e.g. Microsoft's Azure Message Bus or Amazon's Simple Queue Service).
One of the first things to change in the initial contribution will be to define and implement Hono's external messaging interface based on AMQP 1.0 for better interoperability.
Additional steps then include:
- Support for additional device communication protocols by means of additional Protocol Adapters. In particular, we would like to support LWM2M by means of a leshan based Protocol Adapter.
- Support for (existing) messaging infrastructure on public cloud providers.
- Integration with (existing) security infrastructure of public cloud providers and/or IaaS/PaaS stacks.