I found it to be much easier to put haproxy in TCP mode in front of mosquitto than to use mosquitto's TLS capabilities. This lets me reload the certificate without restarting mosquitto.

My local devices (esp8266) can't really handle TLS well, but I want access from outside of my local network to be encrypted. This lets them operate in plain-text mode locally, with firewall rules forcing outside access to be secure.

My approach with a recent personal project (i.e. no actual scaling required) was to have the MQTT server just listen on localhost. Application connects without TLS on the loopback interface. Clients connect over WebSocket (TLS) using their existing OAuth access token as the username and "x" as the password. The application involves an API as well so client credentials are already in use.

I used jpmens/mosquitto-auth-plug <https://github.com/jpmens/mosquitto-auth-plug> for the Mosquitto side of things, with a query along the lines of:

  SELECT "hardcoded password hash" FROM oauth_access_tokens WHERE access_token = "%s" AND scope REGEXP "\bmqtt\b";

We were able to set up a certificate-per-device authorization for MQTT where we use CN field of the cert for mapping to what particular device is allowed to pub/sub to

I use almost the same thing with an Internet accessible MQTT server that acts as relay of Zoom Webhook events, except it is using nginx as the proxy. I have local MQTT server that connects to the public MQTT server and then local clients that show zoom status via LEDs are connected to my local server.

There is also no mention in article of what is being used for internal DNS resolution. I could assume pi-hole, but something to resolve DNS on home network is required is this operation.

This is a good tutorial to get the server side of things secured. I didn't know you could use Traefik to proxy the MQTT connections as well which looks quite useful.

The biggest issue I have is with the client side and its various support of TLS and getting a trusted CA certificate distributed. This is the harder part of the equation in my opinion, support is getting better with firmwares like Tasmota but getting some third party IoT device to work over TLS is still a challenge.

I'm a bit confused. You got a local MQTT server, and a local Traefik proxy, all behind your local firewall. How does Traefik get its LetsEncrypt certificate from behind the firewall when LetsEncrypt can't see Traefik?

The last time I tried to use LetsEncrypt for a local server, several years ago, this could not be done. Has this changed?

You lucky guys with IP stacks and TLS! I had to secure an IoT MQTT install where the packets themselves needed encryption which meant hamfisting in an encapsulated packet scheme (plain text header, end to end encrypted payloads). Kinda painful and I would not do that again!

Securing MQTT is all good and well. It's more difficult with MQTT-SN (lighter weight and lower bandwidth) can run over UDP which is recommended for running over NB-IoT and similar cellular systems.

Could we MQTT in regular applications as well? or just in IOT?

Absolutely yes.

MQTT is a specific implementation of a general approach to buses. This is wildly used for asynchronous communication between services.

I use MQTT (or other buses) when I have services that need to send some information without consideration for the services that need that information. The first ones are producers, the other ones - consumers.

This is a very powerful approach when you have good cases. IoTs are typical cases where they send data and something else makes use of them. Another example is code that calculates some information and emits its results.

Some of my code retrieve google calendar information and emits that - and it is consumed by a dashboard, some other code that makes decisions such as alarm clocks etc.

In general you use this for asynchronous messaging, especially in with one-to-many scenarios.

(Author here)

I run it to communicate with much more applications. It just depends on your own preferences. For example, some tools provide an API (local or cloud based) and you can directly plug in into that API. In The Netherlands you can read your electricity meter yourself by a "Dutch Smart Meter Readings" and DSMR integrates into Home Assistant with MQTT. I use Z-Wave as wireless mesh technology for lights and switches, the Z-Wave controller integrates into Home Assistant with MQTT.

MQTT is so easy to setup and configure, you can use it for any messaging you want. As an example, I run Home Assistant locally to run my home automations, but also check the status of my local devices and online servers (Digital Ocean droplets). One use case is my backup script which publishes the backup results to an online MQTT server, my Home Assistant checks the topics at that server to display backup stats locally. If something went wrong, Home Assistant notifies my directly. PS. The backup script also sends out e-mails which I filter in Fastmail, the success mails are trashed and only error messages are kept in the inbox ;)

In my experience MQTT works well for telemetry and one-way messaging, but it's not good at doing request-response flow like you typically do in an application using HTTP. You can certainly come up with a mechanism for doing that, but you're having to re-invent a lot of what HTTP already solves.

Sure. However if you are thinking for server/cloud usage, I would recommend considering AMQP instead (RabbitMQ etc). Especially if you want a "worker" type model with horizontal scalability for job processing, then the roundrobin.

Some of the functionality has been added to the MQTTv5 spec, but client support is not as good for that yet, and its not as battle tested as AMQP.

MQTT is just a tool for publish/subscribe; that pattern exists in way more domains than IOT. Facebook Messenger, for example, is implemented on top of it.