Hi, I’m a data analyst at a small grocery chain (5 stores), our one IT guy left in the summer and now the sensor project is mine. Sorry if this is basic.
Each store has 6 to 10 ESP32 fridge/freezer temperature sensors and a door counter, all sending to Hermetry over MQTT. Right now they are on the same Wi-Fi as the tills and the office PCs, because that’s how they were set up. Our card payment auditor flagged it.
Options people have suggested to me: (1) put them on the guest Wi-Fi, (2) make a separate VLAN, (3) put a Raspberry Pi in each store and have the sensors talk only to the Pi. I don’t know enough to choose. What would you do? The routers are Ubiquiti, one AP per store.
Guest Wi-Fi seems easiest? It’s already separated from your tills.
Guest networks in shops often have a captive portal or kick clients after a few hours, the ESP32s will hang there. Check that before. Do the sensors need to talk to anything in the store, or only out to the internet?
Only out to Hermetry as far as I know. Nothing local reads them. The guest network does have a “click to accept” page.
Then guest is out. I did this for my sister’s bakery and two cafes, all Ubiquiti, so roughly your setup:
Make a new SSID “store-iot” with WPA2 PSK, tag it to its own VLAN (say 30), turn on client isolation so sensors can’t talk to each other, and in the firewall rules allow that VLAN only outbound: DNS, NTP, and TCP 8883 to the Hermetry broker (443 too if anything uses HTTPS). Block VLAN 30 to every other internal network. That’s what the auditor wants to see, and it’s one afternoon per store.
I wouldn’t add a Pi for this. A Pi is worth it when your devices can’t reach the internet themselves (BLE, Modbus, Zigbee) and something has to report for them as a gateway. Your ESP32s already do TLS on their own, a Pi just adds an SD card that can die in the back office.
On the Hermetry side two cheap extras: on the fridge profile set Allowed networks to each store’s public IP, so a stolen token is useless from anywhere else. And check Plain MQTT is off, TLS only on 8883 is the default but your IT guy may have turned it on while testing. Checklist at the bottom of Device transport security.
First store done Friday with VLAN 30 and isolation, sensors reconnected on their own after I changed the SSID in their config page. You were right about Plain MQTT, it was on, and two sensors were actually using 1883. Moved them to 8883 and turned it off. Allowed networks needed all 5 store IPs on the one profile, that worked fine.
If the ESP32 firmware uses a hardcoded DNS like 8.8.8.8, allow that too, or they’ll fail after the move and you’ll swear the firewall is fine.
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