Diving into IoT development using AWS

I’m more allergic than most people to buzzwords. I cringe big time when companies suddenly start rebranding their products with the word “cloud” or tack on a “2.0”. That said, I realize that the cloud is not just computers in a datacenter and the Internet of Things isn’t all meaningless hype either. There exists a lot of cool new technology, miniaturization, super cheap hardware of all shapes and sizes and power requirements, ever more rapid prototyping and lot more that adds up to what looks like a new era in embedded system hardware.

Diving into IoT development using AWS
People at the embedded linux conference can’t wait to tell you about IoT stuff

But what will drive this hardware? There is a lot of concern about the software that’s going to be running on these internet-connected gadgets because we all just know that the security on most of these things is going to be downright laughable, but now since they’re a part of your car , your baby monitor , your oven , your insulin pump and basically everything, this is gonna be a big problem.

So I’ve embarked on a project to try to build an IoT application properly and securely. I think it’ll be fun, a good learning experience, and even a useful product that I may be able to sell one day. At any rate it’s an interesting technical challenge.

My project is thus: to build a cloud-based IoT (ughhh sorry) IP camera for enterprise surveillance. It will be based on as much open source software as possible, ABRMS-licensed , mobile-first and capable of live streaming without any video transcoding.

I think I know how to do this, I’ve written a great deal of real-time streaming software in the past. I want to offload as much as the hard stuff as possible; let the hardware do all the h.264 encoding and let AWS manage all of the security, message queueing and device state tracking.

At the Dublin gstreamer conference I got to chat up an engineer from Axis, an awesome Swedish company that makes the finest IP cameras money can buy. He informed me that they have a new program called ACAP ( Axis Camera Application Platform ) which essentially lets you write what are essentially “apps” that are software packages that can be uploaded to their cameras. And they’re all running Linux! Sweet!

And recently I also learned of a new IoT service from Amazon AWS. I was dreading the humongo task of writing a whole new database-backed web application and APIs for tracking devices, API keys, device states, authentication, message queueing and all of that nonsense. Well it looks like the fine folks at Amazon already did all the hard work for me !

So I had my first development goal: create a simple AWS-IoT client and get it to run on an Axis camera.

Step one: get access to ACAP

Axis doesn’t really make it very easy to join their development program. None of their API documentation is public. I’m always very wary of companies that feel like they need to keep their interfaces a secret. What are you hiding? What are you afraid of? Seems like a really weird thing to be a control freak about. And it majorly discourages developers from playing around with your platform or knowing about what it can do.

But that is a small trifle compared to joining the program. I filled out a form requesting access to become a developer and was eventually rewarded with a salesbro emailing me that he was busy with meetings for the next week but could hop on a quick call with me to tell me about their program. I informed them that I already wanted to join the program and typed all the relevant words regarding my interest into their form and didn’t need to circle back with someone on a conference call in a few weeks’ time, but they were really insistent that they communicate words via telephone.

After Joe got to give me his spiel on the phone I got approved to join the Axis developer partner program. As far as ACAP they give you a SDK which you can also download as an Ubuntu VirtualBox image. Inside the SDK is a tutorial PDF, several cross-compiler toolchains, some shady Makefile includes, scripts for packaging your app up and some handy precompiled libraries for the various architectures.

Basically the deal is that they give you cross-compilers and an API for accessing bits of the camera’s functionality, things like image capture, event creation, super fancy storage API, built-in HTTP server CGI support, and even video capture (though support told me vidcap super jankity and I shouldn’t use it). The cross-compilers support Ambarella ARM, ARTPEC (a chip of Axis’s design) and some MIPS thing, these being the architectures used in various Axis products. They come with a few libraries all ready to link, including glib, RAPP (RAster Processing Primitives library) and fixmath. Lastly there’s a script that packages your app up, building a fat package for as many architectures as you want, making distribution super simple. Now all I had to do was figure out how to compile and make use of the IoT libraries with this build system.

Building mbedTLS and aws_iot

AWS has three SDKs for their IoT clients: Arduino Yún, node.js and embedded C linux platforms. The Arduino client does sound cool but that’s probably underpowered for doing realtime HD video, and I’m not really the biggest node.js fan . Linux embedded C development is where it is at, on the realz. This is the sort of thing I want to be doing with my life.

Diving into IoT development using AWS

All that I needed to do was create a Makefile that builds the aws_iot client library and TLS support with the Axis toolchain bits. Piece of cake right? No, not really.

The IoT AWS service takes security very seriously, which is super awesome and they deserve props for forcing users to do things correctly: use TLS 1.2, include a server certificate and root CA cert with each device and give each device a private key. Wonderful! Maybe there is hope and the IoT future will not be a total ruinfest. The downside to this strict security of course is that it is an ultra pain in the ass to set up.

You are offered your choice of poison: OpenSSL or mbedTLS. I’d never heard of mbedTLS before but it looked like a nice little library that will get the job done that isn’t a giant bloated pain in the ass to build. OpenSSL has a lot of build issues I won’t go into here.

To set up your app you create a key and cert for a device and then load them up in your code:

connectParams.pRootCALocation = rootCA;  connectParams.pDeviceCertLocation = clientCRT;  connectParams.pDevicePrivateKeyLocation = clientKey;

Simple enough. Only problem was that I was utterly confused by what these files were supposed to be. When you set up a certificate in the IoT web UI it gives you a public key, a private key and a certificate PEM. After a lot of dumbness and AWS support chatting we finally determined that rootCA referred to a secret CA file buried deep within the documentation and the public key was just a bonus file that you didn’t need to use. In case anyone else gets confused as fuck by this like I was you can grab the root CA file from here.

The AWS IoT C SDK (amazon web services internet of things C software development kit) comes with a few sample programs by way of documentation. They demonstrate connecting to the message queue and viewing and updating device shadows.

#define AWS_IOT_MQTT_HOST              "B13C0YHADOLYOV.iot.us-west-2.amazonaws.com" ///< Customer specific MQTT HOST. The same will be used for Thing Shadow                                                                                                                        #define AWS_IOT_MQTT_PORT              8883 ///< default port for MQTT/S                                                                   #define AWS_IOT_MQTT_CLIENT_ID         "MischaTest" ///< MQTT client ID should be unique for every device                                  #define AWS_IOT_MY_THING_NAME          "MischaTest" ///< Thing Name of the Shadow this device is associated with                           #define AWS_IOT_ROOT_CA_FILENAME       "root-ca.pem" ///< Root CA file name                                                                #define AWS_IOT_CERTIFICATE_FILENAME   "1cd9c753bf-certificate.pem.crt" ///< device signed certificate file name                           #define AWS_IOT_PRIVATE_KEY_FILENAME   "1cd9c753bf-private.pem.key" ///< Device private key filename                                      

To get it running you edit the config header file, copy your certificates and run make. Then you can run the program and see it connect and do stuff like send messages.

Diving into IoT development using AWS

Once you’ve got a connection set up from your application to the IoT API you’re good to go. Kind of. Now that I had a simple C application building with the Axis ACAP SDK and a sample AWS IoT application building on linux, the next step was to combine them into the ultimo baller cloud-based camera software. This was not so easy.

Most of my efforts towards this were spent tweaking the Makefile to pull in the mbedTLS code, aws_iot code and my application code in a setup that would allow cross-compiling and some semblance of incremental building. I had to up my Make game considerably but in the end I was victorious. You can see the full Makefile in all its glory here .

The gist of it is that it performs the following steps:

  • loads ACAP make definitions ( include $( AXIS_TOP_DIR ) /tools/build/rules/common.mak)
  • sets logging level (LOG_FLAGS)
  • grab all the source and include files/dirs for mbedTLS and aws_iot
  • define a static library target for all of the aws_iot/mbedTLS code –  Diving into IoT development using AWS
  • produce executable:
    Diving into IoT development using AWS

The advantage of creating aws-iot.a is that I can quickly build changes to my application source without having to re-link dozens of files.

I combined the Axis logging macros and the aws_iot style logging into one syslog-based system so that I can see the full output when the app is running on the device.

Uploading to the Camera

Once I finally had an ACAP application building I was finally able to try deploying it to a real camera (via make target of course):

Diving into IoT development using AWS

Diving into IoT development using AWS

Getting the app running on the camera and outputting useful logging took quite a bit of effort. I really ran into a brick wall with certificate verification however. My first problem was getting the certs into the package, which was just a simple config change. But then it began failing. Eventually I realized it was because the clock on the camera was not set correctly. Realizing the importance of a proper config, including NTP, I wrote a script to configure a new camera via the REST API. I wanted it to be as simple as possible to run so I wrote it without requiring any third party libraries. It also shares the package uploader config for the camera IP and password so if you’ve already entered it you don’t need to again.

With NTP configured at least there are no more certificate expired errors. I’m able to connect just fine on normal x86 linux, but fails to verify the certs when running on the camera. After asking support, they suggest recompiling mbedTLS with -O0 (disable optimizations) when building on ARM. After doing so, it connects and works!

Diving into IoT development using AWS

��:pizza::hamburger: !!!!! Success!

To summarize; at this point we now have an embedded ARM camera device that is able to connect and communicate with the AWS IoT API securely. We can send and receive messages and device shadow states.

So what’s next? Now we need a service for the camera to talk to.

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