Azure Device Provisioning Server over MQTT using x509 Certificates

In a previous post, I showed you how to register a device with Azure’s Device Provisioning Server (DPS) over raw MQTT.  A reader/commenter asked how the process would differ if we used x.509 certificate based authentication vs. the SAS-token based authentication that the article was based on.

Since it’s inevitable that I’ll run across this in a customer situation, I thought I’d tackle it.  Based on the knowledge from the previous article, as well as my article on DPS over the REST APIs, it was pretty straightforward.  The process was nearly identical except for a few fields in the connection information, specifically specifying the iothub root cert, the device cert/key, and leaving off the SAS token.  I’ll cover the details below.

Generating Certs

The steps for generating the device certificates and creating the enrollment in DPS is the same process as outlined in my DPS over REST API article.  Specifically the sections titled “Prep work (aka – how do I generate test certs?)” and “X.509 attestion with individual enrollments- setup”, so I won’t repeat them here…    For the screenshots below, I called my enrollment registration id ‘dpstestdev01’.

The only other thing you need is the IoT Root CA cert.  This is the Baltimore-based root ca cert from which all the IoT Hub and DPS  “server-side” TLS certificates are generated.   The client needs this to validate that it is indeed talking to the genuine microsoft endpoint and not a ‘man in the middle’.   The easiest way to get this cert, is to open this file from the Azure IoT C SDK, copy everything from (and including) line 23 to (and including) line 43, then strip out the quotes at the beginning and end of each line, and strip off the ‘\r\n’ off the ends.  Save the file with a .pem extension.  We will call that the “DPS-root-CA” cert.

Client Setup

You can leverage any MQTT 3.1.1 client to talk to DPS, however, like in previous articles, I’m going to use MQTT.fx, which is an excellent MQTT GUI tool for ‘manually’ doing MQTT.  It allows you to get a really good feel for what’s happening under the covers without writing a bunch of code.

Through a series of screenshots below, I’ll show you my configuration.

The first step is to open Mqtt.Fx, click on the little ‘gear’ button next to the Connect button, and in the bottom right, click on the “+” button to create a new connection.   You can call it anything (I called mine ‘dpscert’ in the screenshots below)

general-settings

This screenshot shows the ‘general’ settings…

  • The type is MQTT Broker
  • The broker address is the global DPS endpoint (global.azure-devices-provisioning.net)
  • The port is the MQTTS (tls) port 8883
  • The client ID is the ‘registration id’ from DPS, specifically in this instance is the CN/Subject name you used for your device cert when you generated it
  • the only other change from the defaults is to explicitly choose MQTT version 3.1.1

user-credentials

This screenshot shows the user credentials.   For DPS, the user-id is of the form of:

{idScope}/registrations/{registration_id}/api-version=2019-03-31

where {idScope} is the idScope of your DPS instance.

Note that, unlike the SAS-Token case, the password is BLANK for x.509 authentication.

ssl-tls-certs

This screenshot is the most important one and the biggest difference from the SAS-Token case.

  • Make sure you explicitly select TLS version 1.2 (we don’t support older versions)
  • in our use case, we are using self-signed certificates, so choose that option
  • For the “CA files”, this the DPS-root-CA cert we captured from github earlier.  (the baltimore root cert)
  • For the Client Certificate file, this is the device certificate we created earlier
  • For the Client Key file, this is the private key for the device cert that we generated earlier.
  • Make sure and check the “PEM formatted” checkbox, as that’s the format our certs are in.

All the other tabs are just left default.

Click Ok to close this dialog.  Click the “Connect” button to connect to DPS.

From this point on, you subscribe and publish exactly like you did in the previous article and/or as specified in the official DPS documentation here.

Enjoy – and as always, let me know if you run into any issue.  Hit me up on Twitter (@BamaSteveB), email (steve.busby ( at ) microsoft.com) or in the comments below.

Azure IoT Device Provisioning Service (DPS) over MQTT

Continuing the theme of “doing things on Azure IoT without using our SDKs”, this article describes how to provision IOT devices with Azure IoT’s Device Provisioning Service over raw MQTT.

Previously, I wrote an article that describes how to leverage Azure IoT’s Device Provisioning Service over its REST API, as well as an article about connecting to IoT Hub/Edge over raw MQTT.  Where possible, I do recommend using our SDKs, as they provide a nice abstraction layer over the supported transport protocols and frees you from all that protocol-level detailed work.  However, we understand there are times and reasons where it’s just a better fit to do things over the raw protocols.

To support this, the Azure IoT DPS engineering team has documented the necessary technical details to register your device via MQTT.   This document may provide enough details for you to figure out how to do it, but since I needed to test it for a customer anyway, I thought I’d capture a real-world example in hopes it can help others.

To make the scenario simpler, I chose to just use symmetric key attestation, but this would still work with any of the attestation methods supported by DPS.

Create individual enrollment

The first step is to create the enrollment in DPS.  In the Azure portal, in your DPS instance, from the ‘overview’ tab, grab your Scope ID from the upper right of the ‘overview’ tab as shown below (I’ve blacked out part of my details, for obvious reasons)

dps-scope-id

Once you have that, copy it somewhere like notepad or equivalent, we’ll use it later.  Once we have that, we can create our enrollment.  On the left nav, click on “Manage Enrollments” and then “Add Individual Enrollment”.  For “Mechanism”, choose Symmetric Key, enter a registration ID of your choosing (for the example further below, I used ‘my-mqtt-dev01’)

create-individual-enrollment

Click Save.  Then drill back into your enrollment in the portal and copy the “Primary Key”  and save it for later use.

Generate SAS token

Once you’ve created the enrollment and gotten the device key, we need to generate a SAS token for authentication to the DPS service.  A description of the SAS token, and several code samples for generating one in various languages can be found here.  Some of the inputs (discussed below) will be different for DPS versus IoT Hub, but the basic structure of the SAS token is the same.

For my purposes, I used this python code to generate mine:

————-

from base64 import b64encode, b64decode
from hashlib import sha256
from time import time
from urllib import quote_plus, urlencode
from hmac import HMAC

def generate_sas_token(uri, key, policy_name, expiry=3600000000):
ttl = time() + expiry
sign_key = “%s\n%d” % ((quote_plus(uri)), int(ttl))
print(sign_key)
signature = b64encode(HMAC(b64decode(key), sign_key, sha256).digest())

rawtoken = {
‘sr’ :  uri,
‘sig’: signature,
‘se’ : str(int(ttl))
}

if policy_name is not None:
rawtoken[‘skn’] = policy_name

return ‘SharedAccessSignature ‘ + urlencode(rawtoken)

uri = ‘[dps URI]’
key = ‘[device key]’
expiry = [SAS token duration]
policy=’registration’

print(generate_sas_token(uri, key, policy, expiry))

——–

where:

  • [dps URI] is of the form [DPS scope id]/registration/[registration id]
  • [device key] is the primary key you saved earlier
  • [SAS token duration] is the number of seconds you want the token to be valid for
  • policy is required to be ‘registration’ for DPS SAS tokens

running this code will give you a SAS token that looks something like this (changing a few random characters to protect my DPS):

SharedAccessSignature sr=0ne00055505%2Fregistrations%2Fmy-mqtt-dev01&skn=registration&sig=gMpllKo7qS1VR31vyfsT6JAcc4%2BHIu2gQSyai0Uz0KM%3D&se=1579698526

Now that we have our authentication credentials, we are ready to make our MQTT call.

Example call

The documentation does a decent job of showing the MQTT parameters and flow (read it first!), so I’m not going to repeat that here.  What I will show is an example call with screenshots to ‘make it real’.   For my testing, I used mqtt.fx, which is a pretty nice little interactive MQTT test client.

Once you download and install it,  click on the little lightning bolt to switch from localhost to allow you to create a new connection to an MQTT server.

mqtt-lightning

After that, click on the settings symbol next to the edit box to open the settings dialog that lets you edit the various connection profiles:

mqttfx-settings-icon

On the “Edit Connection Profiles” dialog, in the very bottom left hand corner, click the “+” symbol to create a new connection profile.

Give your connection a name and choose MQTT Broker as the Profile Type

mqtt-profile-settings-general

Enter the following settings in the top half of the dialog:

  • for “Broker Address”, use ‘global.azure-devices-provisioning.net’
  • for “Broker Port”, use “8883”
  • for Client ID, enter your registration ID you used in the portal for your device

Click on the General ‘tab’ at the bottom.  As in the screenshot above, for MQTT Version, uncheck the “Use Default” button and explicitly choose version 3.1.1.  Leave other settings on this tab alone.

click on the “User Credentials” tab’

  • for “User Name”, enter [DPS Scope Id]/registrations/[registration id]/api-version=2019-03-31  (replacing the scope id and registration id with your values)
  • for “Password”, copy/paste in your SAS token you generated earlier

mqtt-profile-user-creds

Move to the SSL/TLS tab.   Check the box for “Enable SSL/TLS” and make sure that TLSv1.2 is chosen as the protocol

mqtt-profile-tls

leave the proxy and LWT tabs alone.

Click Ok to save the settings and return to the main screen

Click on the Connect button and you should get a successful connection (you can verify by looking at the “log” tab)

Once connected, navigate to the “Subscribe” tab.  We will set up a subscription on the dps ‘response’ MQTT topic to receive responses to our registration attempts from DPS.  On the “Subscribe” tab, enter ‘$dps/registrations/res/#’ into the subscriptions box, choose “QoS1” from the buttons on the right, and click “Subscribe”.  You should see an active subscription get set up and waiting on responses.

mqtt-subscription-setup

Click back over on the “Publish” tab and we will make our registration attempt.  In the publish edit box, enter $dps/registrations/PUT/iotdps-register/?$rid={request_id}

replace {request_id} with an integer of your choosing (1 is fine to start with).  This lets us correlate requests with responses when we get responses back from the service.  For example, I entered:

$dps/registrations/PUT/iotdps-register/?$rid=1

in the big edit box beneath the publish edit box, we need to enter a ‘payload’ for the request.  For DPS registration requests, the payload takes the form of a JSON document like this:  {“registrationId”:”<registration id>”}

for example, for my sample it’s:

{“registrationId”: “my-mqtt-dev01”}

mqtt-reg-publish

Hit the “Publish button”

Flip back over to the Subscribe tab and you should see on the right hand side of the screen that we’ve received a response from DPS.  You should see something like this:

mqtt-registration-assigning

This indicates that DPS is in the process of ‘assigning’ and registering our device to an IoT Hub.  This is a potentially long running operation, so to get the status of it, we have to query for that status.  To do that, we are going to publish another MQTT message to check on the status.  For that, we need the ‘operationId’ from the message we just received.  In the screenshot above, mine looks like this:

4.22724a0213a69c4d.9750f5e6-b4c3-4760-9b15-4e74d6120bd1

Copy that ID as we’ll use it in the next step.

To check on the status of the operation, switch back over to the Publish tab and replace the values in the publish edit box with this

$dps/registrations/GET/iotdps-get-operationstatus/?$rid={request_id}&operationId={operationId}

replacing {request_id} with a new request id (2 in my case) and the {operationId} with the operationId you just copied. For example, with my sample values and the response received above, my request looks like this:

$dps/registrations/GET/iotdps-get-operationstatus/?$rid=2&operationId=4.22724a0213a69c4d.9750f5e6-b4c3-4760-9b15-4e74d6120bd1

Delete the JSON in the payload box and click “publish”

Switch back over to the Subscribe tab and you should notice that you’ve received a response to your operational status query, similar to this:

mqtt-registration-status

Notice the status of “assigned”, as well as details like “assignedHub” that gives the state of the successful registration and connection details.

If you navigate back over to the azure portal and look at the enrollment record for your device (refresh the page.. you may have to exit and re-enter), you should see something like this:

mqtt-registration-success

This indicates that our DPS registration was successful.

In the “real world”, in your application, you’ll make the registration attempt and then poll the operational status until it gets to the state of ‘assigned’.  There will be intermediate states while it is being assigned, but doing this manually through a GUI, I’m not fast enough to catch them Smile

Enjoy – and let me know in the comments if you have any questions or issues.

Quick update on MQTT and message routing in IoT Hub and IoT Edge

I’ve made an update to my posts on using a standard MQTT client and using Node-Red to connect to IoT Edge via MQTT.

One thing I missed in the original post, that I needed to figure out today for a customer, is that if you want to route messages in IoT Edge based on the message body, you need to use the contentType and contentEncoding fields to tell edgeHub that the content is, in fact, JSON, and also what encoding it is (i.e. utf-8, utf-16, etc). This is not unique to IoT Edge, but a requirement for IoT Hub itself as well.

The way you do that is by appending ‘properties’ to the end of your MQTT topic to indicated the content type and the content encoding. In MQTT, those are the $.ct and $.ce properties, respectively.. So, regardless of your client, you do that by appending the values $.ct=application/json and $.ce=utf-8, after URL encoding them, to your topic, like this:

devices/[device_id]/messages/events/$.ct=application%2Fjson&$.ce=utf-8

where [device_id] is obviously the device id in iot hub of your sending device. This allows you to do things like this in your IoT Edge routing (pretend we are sending a message like {“messageType”:”alert”, ……})

{
"routeToAlertHandler":"FROM /messages/* WHERE $body.messageType='alert' INTO ........
}

Enjoy! and, as always, if you have any questions, hit me up in the comments section or twitter/etc (links in my ‘about me’ page)

Connect Node-Red to Azure IoT Edge

NOTE:  updated on 2/14/2019 to add the note about adding the content type and content encoding to the MQTT topic if you want to route messages based on the message body in IoT Edge

Recently on behalf of a customer, I was asked if it was possible to connect Node-Red to Azure IoT Edge.  Node-Red, an IBM sponsored graphical process design tool, is increasingly popular in IoT scenarios.

My first thought was “well sure, there is an IoT Hub ‘node’ for Node-Red, surely it can be used for connecting to IoT Edge”.  Well, looks like it can’t.   For two reasons, 1) it’s not designed to do that (no way to specify the edge box/GatewayHostName) and 2) it’s not very good  Smile.  There are a couple of other options out there, too, but none of the IoT Hub specific ‘nodes’ will work for this use case.

Secondly, and this is really cool, my Azure IoT Global Black Belt peers in Europe have developed an IoT Edge module that hosts Node-Red inside Edge itself, where you can orchestrate your IoT process, and have it drop messages on edgeHub for further edge processing and/or uploading of messages to IoT Hub.   *If* you are interested in hosting and managing Node-Red from inside IoT Edge itself, you should definitely check it out.  It’s really nice.

With that said, a lot of customers (including the one that prompted this post) either already have a Node-Red environment outside of IoT Edge, or just for a host of reasons want to keep them separate.  If so, this post is for you.   Since the IoT Hub ‘node’ won’t seem to work for this use case, we are going to use the MQTT node.  One thing to note – this only addressed device-to-cloud telemetry.  I haven’t (yet) addressed cloud-to-device management/messages/configuration because my customer’s use case didn’t (yet) need it.  Baby steps.

First of all, let’s get some pre-requisites out of the way.

Pre-requisites

For this post, I assume a number of things:

  • You’ve already got a Node-Red environment up and going.  If not, follow the directions to do so from the Node-Red site.    I also assume you have some familiarity with Node-Red.  If you don’t, they have some nice tutorials on the site.  Make sure Node-Red is running   (node-red-start from the command prompt)
  • You already have Azure IoT Edge setup as a transparent gateway and have confirmed that you can connect to it over the 8883 MQTT using the handy openssl command included in the docs (this is necessary because Node-Red will be connecting to IoT Edge as a “leaf” or “downstream” device).  NOTE:  make sure that whatever name you use in the hostname parameter in your config.yaml file is the same resolvable name that you will use from Node-Red to connect to the IoT Edge box.  If you have to change it in config.yaml to match, restart iot edge before proceeding.
  • From your IoT Edge box, copy/download/ftp/whatever the root CA cert that was used to set up the IoT Edge box.  If you used a ‘real’ cert (i.e. from DigiCert, Baltimore, etc), then you’ll need to get the public key cert from them in the form of a pem or crt file.  If you used the convenience scripts from the transparent gateway instructions above, it’s the cert labeled azure-iot-test-only.root.ca.cert.pem in the ‘certs’ folder underneath whatever folder you generated your certs in.   Just grab that file and get it to your local desktop, we’ll need it later.
  • Your IoT Edge box is reachable, network-wise, from your Node-Red box.  Can you ping it?  Can you resolve it’s DNS name?  Can you telnet to 8883?

In my case, I ran everything (Node-Red and IoT Edge both) from a single Raspberry Pi that I had laying around.  But beyond the requirements for Node-Red and IoT Edge themselves, there is no requirement for specific OS’es or co-location, as long as they can see each other on the network, and IoT Edge can get to IoT Hub.

Setup

Ok, enough caveating and pre-req’ing, let’s do some setup.

One of the things you will need is an IoT Hub device identity in the hub to represent our Node-Red flow.  If you haven’t already, create an IoT Device to represent our Node-Red “device” (the flow).  Go ahead and capture the “device id”, and URI of the Hub (something.azure-devices.net).

You will also need a Shared Access Signature, a token that authenticates the device to IoT Hub.  The easiest way to generate one is to open up a cloud shell instance in the azure portal.   To do that, click on the Cloud Shell button in the top nav part of the portal.  It looks like this:

cloud-cli

You may have to go through some preliminary setup (select a blob storage account, etc) if it’s the first time you’ve done it.  You can use either Powershell or Bash.  I prefer Bash myself, but both work.

Once the cloud shell is created and you have a command prompt, the first thing we have to to do install the azure iot hub extension for the azure cli interface.   You can do this by running this command

az extension add –name azure-cli-iot-ext

You only have to do it the first time, it ‘sticks’ for subsequent times you use the cloud shell.  Once this is done, you can generate your SAS token with this command:

az iot hub generate-sas-token –d [device id]-n [hub name] –du [duration]

where [device id] is the device id from the device you created earlier, [hub name] is the short name of your IoT Hub (with the .azure-devices.net) and [duration] is the amount of time, in seconds, you want your toke to be valid.  Shorter values are more secure, but longer values are easier to manage (you have to re-create and re-configure the token in Node-Red when it expires).  It’s up to you to figure out your best balance between security and convenience Smile.  I will remain silent on the topic here.

Once you generate your token, you need to copy it somewhere, as we’ll need it later.  The process will look something like this (click on the picture to enlarge):

sas-token

You need the part that starts with “Shared Access Signature”, without the quotes.  Highlighted in yellow in the picture.     NOTE in the picture that ‘sdbiothub1’ is the name of my IoT Hub used in this demo.  Also note that I used a duration of 60 seconds, so you can’t monkey with my IoT Hub.  Not that you would ever do anything like that.

Ok, we have all the information we need to get started.

IoT Edge and IoT Hub debug prep

There’s really nothing else we need to do in order to get IoT Edge and IoT Hub ready, but we’ll do a couple of things to have them ready in the background to both debug our Node-Red setup and see the messages flow through if when we are successful.

On the IoT Edge box, run

iotedge logs –f edgeHub

This brings the edgeHub logs up and ‘follows’ them so we’ll be able to see our Node-Red box connect.

In the cloud shell that you have open in Azure, run this command

az iot hub monitor-events –n [hub name] –timeout 0

where [hub name] is your IoT Hub name as before.  This will monitor messages that make it to IoT Hub so we can see our messages flow in from Node-Red.

Just leave those things up and running in the background and we’ll come back to them later (you can CTRL-C to get out of them later when ready)

Let’s set up our Node-Red instance.

Node-Red configuration

On your Node-Red box, bring up the Node-Red configuration page in your browser (typically http://nameofyournoderedbox:1880)

You’ll have a blank canvas.  You can do something more sophisticated later, but for now we’ll just do a VERY simple flow to show messages flowing to IoT Edge.   We are using a very simple flow for two reasons — to show just the main concept of connecting to IoT Edge and because my Node-Red skills are every bit as awesome as my blog writing skills.

From the node palette on the left hand side, grab the MQTT node from the *output* (not input) section of the palette and drop it on the design canvas.  Also grab an Inject node from the input section and drop it on the canvas.    Connect the output of the Inject node into the input of the MQTT node, as shown  below (your MQTT node won’t say ‘connected’ yet).

node-red-canvas

Double click on the MQTT node to configure it.

  • In the ‘name’ field at the bottom, just give it a name you like.  Doesn’t matter what it is
  • For QOS, choose either 0 or 1 .  IoT Hub/Edge do not support QOS 2.
  • For the TOPIC, enter devices/[device id]/messages/events   (where [device id] is the device id you registered earlier in IoT Hub)
  • NOTE:  *if* your payload is JSON, and *if* you think you might want to do routing of the messages based on the *body* of the message, you need to send a content type of ‘application/json’ and a content encoding of ‘utf-8’  (or 16, etc).  to do that, we need to append that information (url-encoded) to the MQTT topic, which gets passed in as a system property.  So, in that case, the ‘topic’ call would look like this (note the ‘/$.ct=application%2Fjson&$.ce=utf-8’ appended to the MQTT topic)
    • devices/[device id]/messages/events/$.ct=application%2Fjson&$.ce=utf-8

Below is a screen shot of mine.  Ignore the “Server” field in the screenshot, as we haven’t configured that yet.  For my ‘device id’, I called my device nodeRedTest for this and subsequent screenshots

mqtt-node-config

I have Retain set to false, but I really have no idea if that makes any difference or not.  I’m not a Node-Red or MQTT expert, although I do play one on conference calls with customers Smile.

Ok, next we will configure our ‘server’.  Click on the little edit pencil next to the Server box

Give your ‘server’ a name (doesn’t matter what it is – I called mine iothub-mqtt in the screenshots).  On the Connection Tab,

  • for the Server  box, enter the hostname of your IoT Edge box (exactly as it’s specified in config.yaml and we verified we could resolve earlier)
  • Change the port from 1883 to 8883  (the MQTT over TLS port)
  • CHECK the Enable Secure (SSL/TLS) connection box.  We will come back and configure that in a moment.
  • For the “Client ID” box, enter your IoT device ID from earlier
  • UNCHECK the “use legacy MQTT 3.1 support” box.  IoT Edge does not support legacy MQTT connections

Example values based on my setup are shown below.  ‘rpihat1’ is the hostname of my IoT Edge box.

mqtt-node-connection

Click on the ‘Security’ Tab

  • For the username, enter  “[hub name].azure-devices.net/[device id]/api-version=2016-11-14”  (filling in your values for hub name and device id)
  • For the password, paste in the SAS token, in it’s entirety that you copied earlier

A sample screenshot of mine is below

mqtt-node-security

You don’t need to set or change anything on the Messages tab

Back on the Connections Tab, next to the “TLS Configuration” box, click on the edit/pencil button

Next to “CA Certificate”  (the fourth button down), click “Upload”.  Upload the root CA certificate that you downloaded earlier.

For the name at the bottom, just make up a meaningful name for this config and click Save

Click Save or Update on the main node configuration box to save all our values and close it as well

We are now ready to save our flow.  Click “Deploy” in the upper right to save and deploy your flow.

Checking progress

At this point your flow is running and you should see your MQTT node status as “Connecting” with a yellow dot next to it.  Flip over to your IoT Edge box and look at the edgeHub logs.  You should see something like this….  (it may take a minute or more to look like this)

edgehub-logs

For some unexplained reason, the TLS Handshake between the Node-Red box and my IoT Edge box fails exactly seven times before it successfully connects.  I have no idea why and haven’t (and probably won’t) put in the effort to troubleshoot.  I suspect it’s related to a a 10-second delay between tries and the 60-second refresh value in the node config..  but who knows?

Eventually you should see the successful connection in the logs as shown the bottom half of the picture above.

If you flip back over to your Node-Red canvas, you should have a green dot next to your MQTT node and it should say “connected”

We just left the Inject node configured with it’s default of “timestamp”…  it really doesn’t matter what we send our IoT Hub at this point, we just want to see messages go in, and an updating timestamp every time we send a message is handy.  NOTE that the Inject node sends ‘timestamps’ in Unix Epoch time (number of seconds since Jan 1, 1970) so it just looks like a big number.

click on the little button (circled in red below) on the Inject node in the Node-Red canvas

inject-button

This will cause a message to be created and sent to the MQTT node for sending to IoT Edge.  That will, in turn, send the message up to IoT Hub.

Flip over to your Azure Portal browser window and you should see your message having made it to IoT Hub.  click on the Inject button a few more times to send a few more messages (because it’s fun)

The output should look something like this

iothub-debug

Your Node-Red installation is now connected and sending messages through IoT Edge up to IoT Hub.  You can now make your Node-Red flow more sophisticated (reading from sensors, etc) and do any and all the goodness that comes with IoT Edge (stream processing, custom modules, machine learning, etc).

If you have any questions or feedback, please leave them in the ‘comments’ section below.

Enjoy!

Mosquitto MQTT broker to IoT Hub/IoT Edge

 

EDIT:  edited on 8/30 to change tls version to tls 1.2.  Seems that TLS 1.0 doesn’t work any more.  Thanks to Asish Sinha for the heads up.  Also updated the api-version to the latest

 

Earlier, I had a post on connecting an MQTT client to IoT Edge.

It seems like lately my team and I have had a lot of customers with brownfield equipment that can speak MQTT, but are either too old or too low powered (the devices, not the customers Smile)  to do MQTT over TLS.  It is also often the case that you have no real control over the MQTT topic(s) that the device sends events/messages over.  Additionally, many devices even imply “intelligence” or “data” into the topic structure, meaning the topic hierarchy itself conveys information vs. only having important information in the message payload.

Both a TLS connection, and sending data on a very specific topic, are current requirements to talk to either IoT Edge or IoT Hub itself over MQTT.   So, how do we overcome this impedance mismatch between what IoT Hub/Edge requires, and the equipment can do?   One way is to use a middle layer to do the translations.  A popular choice is the open source MQTT broker mosquitto from the Eclipse Foundation.   Mosquitto has a built-in option to set up an MQTT “bridge”, in which the broker will accept incoming messages over MQTT and then forward them as an MQTT client to another MQTT server.  The good news is, Mosquitto can listen to the unencrypted MQTT traffic (port 1883 by default), and then forward it along over a TLS-protected MQTTS connection (port 8883) via this bridge. 

That takes care of our MQTT vs. MQTTs issue.  But what about the any topic vs. a specific topic problem.  Unfortunately, IoT Hub and IoT Edge both only accept telemetry/event data on a specific MQTT topic:  devices/[device-id]/messages/events where [device-id] is the ID of the connected device.  That one is a little trickier, and will be addressed later in this post after we cover the basics of setting up the bridge.

A couple of notes/caveats before we get started:

  • I am NOT a mosquitto expert.  I’ve learned just enough to get this working Smile
  • This is certainly not the only way to solve this problem.  But is one way that seems to work pretty well.
Mosquitto Bridge Setup for IoT Hub/Edge

Before we can configure our Mosquitto MQTT bridge, there are a few pre-requisites to take care of 

  • If you don’t already have one, create an IoT Hub and create a device (only follow that one section) that will represent our Mosquitto broker. The messages in IoT Hub/Edge will appear as if they come from the broker as the IoT device.
  • If you are talking directly to IoT Hub, you can skip this step.  If you are wanting to route your messages through IoT Edge, you need to setup an IoT Edge device as a gateway.
  • Gather the TLS server-side root certificate.  In order for mosquitto to establish a TLS connection to either IoT Hub or IoT Edge, it needs to trust the server-side TLS certificate that will be presented to the broker when it tries to open the connection to IoT Hub/Edge.  Gathering the CA cert from which the TLS server-side cert was generated, the process differs slightly based on whether you are connecting to IoT Hub or IoT Edge.  Either way, save the cert to a file on the mosquitto server, we’ll use it later.

For IoT Hub, the TLS certificate chains up to the public DigiCert Baltimore Root certificate. You can create this file by copying the certificate information from certs.c in the Azure IoT SDK for C. Include the lines —–BEGIN CERTIFICATE—– and —–END CERTIFICATE—–, remove the ” marks at the beginning and end of every line, and remove the \r\n characters at the end of every line.  Name the file with a .pem extension.

For IoT Edge, use whatever root certificate you used to create the IoT Edge Device CA Certificate.  If you used our convenience scripts to set up IoT Edge, that will be the azure-iot-test-only.root.ca.cert.pem found in the ‘certs’ folder where you ran the scripts

Now that we have our pre-req’s finished, we can do our Mosquitto  bridge setup.  This is done via the Mosquitto configuration file.   There may be other things in that file, however, below is an example configuration entry.


# Bridge configuration
connection azureiot-bridge
log_type debug
address [edge or hub fqdn]:8883
remote_username [iothub-shortname].azure-devices.net/[device-id]/api-version=2019-03-31
remote_password [sas-token]
remote_clientid [device-id]
bridge_cafile [iot hub or edge root ca cert]
try_private false
cleansession true
start_type automatic
bridge_insecure false
bridge_protocol_version mqttv311
bridge_tls_version tlsv1.2
notifications false
notification_topic events/

topic devices/[device-id]/messages/events/# out 1

The parts in bold need to be replaced with your values, where

  • [iot hub or edge FQDN] is the DNS name of either your IoT Hub (including the .azure-devices.net) or your IoT Edge device  (i.e. whatever name was used as the ‘hostname’ in config.yaml on IoT Edge)
  • [iothub-shortname] is the name of your IoT Hub  (e.g. ‘myiothub’) without the .azure-devices.net
  • [device-id] is the name of the IoT device created in IoT Hub to represent this broker
  • [sas-token] is a SAS token generated for that device-id in that hub
  • [iot hub or edge root ca cert] is the full path to the root certificate file you created earlier
  • All values are case sensitive.

The very last line (that starts with the word ‘topic’) subscribes the bridge to all messages that are sent with the topic structure of ‘devices/[device-id]/messages/events/#’ (the # is a wildcard to include any sub-topics). When a message that fits that topic structure gets published, the bridge will get it and pass it along to the IoT Hub/Edge.

restart your Mosquitto broker using the updated configuration file.  You should see debug output indicating that it has connected the bridge (and if you are using IoT Edge, you should see debug output in the edgeHub logs showing the connection from the broker)

If you want to test the connection, you can send a test message using the mosquitto_pub command, using the following command (replacing [device-id] with your device id you created above):


mosquitto_pub -t devices/[device-id]/messages/events/ -m "hello world!"

The trailing slash is important and required. You should see the message above be forwarded by the MQTT bridge to either IoT Hub or IoT Edge.

If you are fortunate enough to have full control over your MQTT topic structure from your devices, and there is no intelligence in your topic structure, you’re done.  Congrat’s and have fun!  You can just point your MQTT clients at the broker address (making sure you update the MQTT topic to point to devices/[device-id]/messages/events/) and rock and roll.

However, for the use cases where you don’t have MQTT topic control, or there is intelligence in your topic hierarchy, keep reading.

MQTT Topic Translation

Unfortunately, this is where things get a little less “clean”.  The mosquitto MQTT bridge has no ability to “rewrite” or completely change the topic structure of the messages it receives.  One way to do it is to write a simple client that subscribes to all potential topics from which the MQTT devices might send data, and then resend the payload after translating the MQTT topic into the IoT Hub/Edge required topic structure. 

Below is a simple python script that I wrote to do the translation as an example.  This sample subscribes to all topics (#  – the wildcard) and, if the message doesn’t already use the IoT Hub/Edge topic structure, it simply resends the message payload using the hub/edge topic.


import paho.mqtt.client as mqtt
import time

#replace [device-id] with your device you created in IoT Hub.
iothubmqtttopic = "devices/[device-id]/messages/events/"

# this sample just resends the incoming message (on any topic) and just
# resends it on the iothub topic structure.  you could, of course, do any
# kind of sophisticated processing here you wanted...
def on_message(client, userdata, message):
     global iothubmqtttopic
     if(message.topic != iothubmqtttopic):
         messageStr = str(message.payload.decode("utf-8"))
         print("message received " ,messageStr)
         print("message topic=",message.topic)
         client.publish(iothubmqtttopic, messageStr)

# replace &lt;broker address> with the FQDN or IP address of your MQTT broker
broker_address="[broker address]"

print("creating new instance")
client = mqtt.Client("iottopicxlate") #create new instance
client.on_message=on_message #attach function to callback
print("connecting to broker")
client.connect(broker_address) #connect to broker

print("Subscribing to all topics")
client.subscribe("#")

client.loop_forever() #stop the loop

Of course, this is one extremely simple example, that just passes along the same message payload and swaps out the message topic.  You can, of course, add any kind of sophisticated logic you need.  For example, you could parse the topic hierarchy, pull out any ‘intelligence’ in it, and add that to the message payload before sending.

if you want to test this, copy this python script to a file, edit it to add your device id and URI of your mosquitto broker, and run it.  You can then try….


mosquitto_pub –t /any/topic/structure/you/want –m "hello world"

You should see the python script receive the file, do the translation, and republish the message.  Then the mosquitto bridge will forward the new message along to IoT Hub/Edge.

Connect Kepware KEPServerEX through Azure IoT Edge to IoT Hub

TLDR: I’ve put together step-by-step instruction on how to leverage Kepware’s IoT Gateway as an MQTT-based “leaf IoT device” for IoT Edge.

I’ve gotten the request a few times from customers who leverage, or want to leverage Kepware for connectivity to their manufacturing equipment and then send that data to IoT Hub through Azure IoT Edge. 

Microsoft’s recommended solution is to leverage OPC-UA and our IoT Edge OPC-UA publisher.  OPC-UA is both a nice industrial protocol, but more importantly, offers a robust data format that plugs in nicely into other Azure services. 

However, in cases where customers either can’t, or don’t want to leverage OPC-UA, Kepware already published a nice technical note showing how to connect Kepware via MQTT directly to Azure IoT Hub via Kepware’s IoT Gateway and MQTT.  However, customers are interested in how to have the data flow through Azure IoT Edge to take advantage of the many nice edge-processing capabilities available.

So, based on the same principals as my “Connect MQTT client to Azure IoT Edge” post, I’ve put together step-by-step instruction on how to leverage Kepware’s IoT Gateway as an MQTT-based “leaf IoT device” for IoT Edge.

You can check out the instructions here.

Enjoy

S

Connect MQTT client to Azure IoT Edge

NOTE:  Edited on 9/13/2018 to fix bugs in code and make it send data in a loop, just to be more realistic test

NOTE:  Edited on 2/14/2019 (Happy Valentine’s Day!) to add the contentType and contentEncoding values to allow you to route on message bodies.

As you may know, MSFT provides some nice SDKs to connect devices to IoT Hub.  Those SDKs abstract away much of the complexity of connecting, protocol abstraction, device twins, direct methods, etc.

However, there are many reasons, in particular “brownfield” devices, where you might prefer to connect via an open source MQTT library, like the nice Paho MQTT library, directly to IoT Hub.  The IoT product group has put together a very good description and sample code for connecting your MQTT device directly to IoT Hub.

With the general availability of Azure IoT Edge, the natural next question is “Can I connect my MQTT devices to IoT Hub *through* IoT Edge?”.  This lets you take advantage of all the nice local processing and cloud services you can pull to the Edge, but make minimal changes to your MQTT-based IoT devices.

The short answer is YES!  For the (only slightly) longer answer, keep reading.

There are only a few steps needed to make this happen.

  • If you haven’t done it yet, you need to set up IoT Edge as a transparent gateway.   The instructions for that are here (linux) and here (windows)….(don’t read too much into the “transparent” part of that, as you can still add other modules such as custom code, Azure ML, Stream Analytics, etc)
  • The MQTT client will establish a TLS connection to the IoT Edge device.  As such, it needs to trust the server certificate that the edgeHub component of IoT Edge presents to it.  For the MQTT/TLS connection to work, depending on the MQTT client (I use the paho-mqtt library below, just like the IoT team did), you’ll likely need the “root ca” certificate that was used to generate the device ca certificate used in IoT Edge.  If you used our test scripts provided at the links in step 1 above, then the certificate you need is at $CERTDIR/azure-iot-test-only.root.ca.cert.pem  (where $CERTDIR is the same one from step 1).  If you used a “real” certificate authority, like Baltimore, DigiCert, etc, they each generally have a method to get their public signing certs.   (we happen to have a couple of them here).   You will need to have them in a file you can reference on the file system of the MQTT box.
  • Your MQTT client needs to be able to resolve the hostname of your IoT Edge box (i.e. you should be able to ping it by name).  If you used a “real” FQDN in DNS for your IoT Edge box, then you are good.  If you didn’t, you may have to add a “hosts” file entry (/etc/hosts on Linux or \windows\system32\drivers\etc\hosts on Windows) to resolve the name.   This name should match the “hostname” parameter from the IoT Edge’s config.yaml file.
  • Finally, we need to make a few minor modifications to the sample code provided by the IoT product group, as seen below…   The biggest change is that, while we still need to authenticate the device to IoT Hub with a valid SAS token for the IoT Hub (and thus the credentials stay the same as the direct case), the actual connection point will be edgeHub.

The code changes to the python script are shown below.  I’ve commented each change with a comment starting with #EDGE. Also, if you copy and paste the code, my blog editor doesn’t respect spaces, so you need to indent the lines under the on_xxxx function definitions, and the code under the while(True) statement

from paho.mqtt import client as mqtt
import ssl

import time

path_to_root_cert = '[path to root CA cert]' # e.g. './azure-iot-test-only.root.ca.cert.pem'
device_id = "[iot device id]" # e.g. "myIoTDevice"
sas_token = "[generated SAS token]" # e.g. SharedAccessSignature sr=exampleIotHub.azure-devices.net%2Fdevices%2FmyIoTDevice&amp;sig=8%2Fo6sdsFE%2BplYLQJrxIo5Usx1iVV0gnySaVhkh7aNOk%3D&amp;se=1563635795"
iot_hub_name = "[iothub short name]" #e.g. exampleIoTHub

#EDGE - the FQDN of the device.. for example: myedgedevice.local
edge_device_name = "[edge device name]"

def on_connect(client, userdata, flags, rc):
print ("Device connected with result code: " + str(rc))
def on_disconnect(client, userdata, rc):
print ("Device disconnected with result code: " + str(rc))
def on_publish(client, userdata, mid):
print ("Device sent message")

client = mqtt.Client(client_id=device_id, protocol=mqtt.MQTTv311)

client.on_connect = on_connect
client.on_disconnect = on_disconnect
client.on_publish = on_publish

#EDGE - we need to add the + "/api-version=2016-11-14" (api version) to the end of the username. Technically, you can do this if you are
# talking directly to IoTHub as well, but it's optional. Edge seems to require it.
client.username_pw_set(username=iot_hub_name+".azure-devices.net/" + device_id + "/api-version=2016-11-14", password=sas_token)

client.tls_set(ca_certs=path_to_root_cert, certfile=None, keyfile=None, cert_reqs=ssl.CERT_REQUIRED, tls_version=ssl.PROTOCOL_TLSv1, ciphers=None)
client.tls_insecure_set(False)

# start paho's background processing

client.loop_start()

#EDGE - although we are still authenticating to IoTHub with the IoTHub based SAS token, we are actually connecting
# to IoT Edge device's MQTT endpoint

client.connect(edge_device_name, port=8883)

i=0

while(True):

payload = "{"message_id": %d}" % (i)

client.publish("devices/" + device_id + "/messages/events/", payload, qos=1)

time.sleep(5)

i=i+1

NOTE:  *if* your payload is JSON, and *if* you think you might want to do routing of the messages based on the *body* of the message, you need to send a content type of ‘application/json’ and a content encoding of ‘utf-8’  (or 16, etc).  to do that, we need to append that information (url-encoded) to the MQTT topic, which gets passed in as a system property.  So, in that case, the ‘publish’ call would look like this (note the ‘/$.ct=application%2Fjson&$.ce=utf-8’ appended to the MQTT topic)

client.publish(“devices/” + device_id + “/messages/events/$.ct=application%2Fjson&$.ce=utf-8”, payload, qos=1)

That’s it. At this point you should be able to run your script and see the successful connection reflected in your edgeHub logs (docker logs -f edgeHub) and, assuming you have the default route set (“FROM /* INTO $upstream”), see the data flowing into IoTHub. (note that the sample app only sends one message and then stops… CTRL-C to exit and run again).

Enjoy!