Building an application for a connected device like a mobile phone, tablet, or a microcomputer is easier than ever these days. A variety of tools and supported programming languages allow developers to quickly build applications that collect sensor data, capture telemetry information or location data, and send the collected information to backend services for processing.
Connected devices communication challenges
A functional prototype can often be built in a matter of days or even hours but a number of challenges arise and must be addressed in order to prepare the application for a wider distribution. Some of the most common challenges are:
- Platform support – applications running on various platforms must be able to send information.
- Reliability – the backend service must be able to reliably accept information.
- Security – only authorized devices should be able to send information and the information must be protected from unauthorized access and manipulation.
- Latency – the network calls must be as quick as possible to avoid network interruptions, preserve system resources and battery power.
- Scalability – in many cases, the backend service must be able to handle massive amounts of data.
It is obviously possible to build a custom solution that satisfies all of your application-specific requirements but would it bring you any business value or would you rather focus on the actual application functionality? Luckily, there are cloud services specifically designed for these types of scenarios, and they can significantly simplify your development efforts.
Azure Event Hubs service introduction
Meet Azure Event Hubs – a highly scalable, low latency and high availability event ingestor service capable of reliably handling millions of events per second and buffering them for further processing for anywhere from 24 hours up to 7 days. The service supports HTTP and AMQP protocols which makes it an attractive option for a wide variety of devices and platforms.
The Event Hubs REST API is pretty straight-forward and easy to use. Simply submit an HTTP POST request to your event hub endpoint and set the request body to a JSON-encoded string that contains one or more messages. For example, below is a sample Send Event request, courtesy of Event Hubs REST API Reference on MSDN.
POST https://your-namespace.servicebus.windows.net/your-event-hub/messages?timeout=60&api-version=2014-01 HTTP/1.1
Authorization: SharedAccessSignature sr=your-namespace.servicebus.windows.net&sig=tYu8qdH563Pc96Lky0SFs5PhbGnljF7mLYQwCZmk9M0%3d&se=1403736877&skn=RootManageSharedAccessKey
Content-Type: application/atom+xml;type=entry;charset=utf-8
Host: your-namespace.servicebus.windows.net
Content-Length: 42
Expect: 100-continue
{ "DeviceId":"dev-01", "Temperature":"37.0" }
Generating a request like this should not require much effort in any programming language on any platform, be it a mobile app or a Node.js application running on a Raspberry Pi. The only part that deserves special attention is the Authorization request header. The Authorization header contains a Shared Access Signature (SAS) token that can be generated by any client that has access to the signing key specified in the shared access authorization rule. Below are some of the best practices to follow when generating SAS tokens for connected devices.
Azure Event Hubs SAS token generation best practices
- Never use the RootManageSharedAccessKey shared access policy to generate SAS tokens for your connected devices since it’s a highly privileged policy. Follow the principle of least privilege and always create a new policy with Send-only permission for each event hub.
- Never send or store your policy keys on connected devices as it may expose your keys for unauthorized access and makes it difficult to rotate or revoke them. Always generate your SAS tokens on the server and only store the generated tokens on the devices.
- Never generate SAS tokens and submit HTTP POST requests to the common event hub URI as the same SAS token would be valid for any device. Always target unique device-specific event hub endpoints when generating tokens and publishing events.
Additional resources