Okay, so let me tell you about my doorbell, from a #networking perspective.
When you push the button by the door, it sends a message over the #zigbee wireless mesh network in my house. It probably goes through a few hops, getting relayed along the way by the various Zigbee light switches and "smart outlets" I have.
Once it makes it to my utility closet, it's received by a Zigbee-to-USB dongle, through a USB hub (a simple tree network) plugged into an SFF PC. From there, it gets fed into zigbee2mqtt, which, as the name implies, publishes it to my local #mqtt broker.
The mqtt broker is in the small #kubernetes cluster of #raspberrypi nodes I run in my utility closet. To get in (via a couple of #ethernet switch hops), it goes through #metallb, which is basically a proxy-ARP type service that advertises the IP address for the mqtt endpoint to the rest of my network, then passes the traffic to the appropriate container via a #linux veth device.
I have #HomeAssistant, running in the same Kubernetes cluster, subscribed to these events. Within Kubernetes, the message goes through the CNI plugin that I use, #flannel. If the message has to pass between hosts, Flannel encapsulates it in VXLAN, so that it can be directed to the correct veth on the destination host.
Because I like #NodeRed for automation tasks more than HomeAssistant, your press of the doorbell takes another hop within the Kubernetes cluster (via a REST call) so that NodeRed can decide whether it's within the time of day I want the doorbell to ring, etc. If we're all good, NodeRed publishes an mqtt message (more VXLANs, veths, etc.)
(Oh and it also sends a notification to my phone, which means another trip through the HomeAssistant container, and leaving my home network involves another soup of acronyms including VLANs, PoE, QoS, PPPoE, NAT or IPv6, DoH, and GPON. And maybe it goes over 5G depending on where my phone is.)
Of course something's got to actually make the "ding dong" sound, and that's another Raspberry Pi that sits on top of my grandmother clock. So to get *there* the message hops through a couple Ethernet switches and my home WiFi, where it gets received by a little custom daemon I wrote that plays the sound via an attached #HiFiBerry board. Oh but wait! We're not quite done with networking, because the sound gets played through PulseAudio, which is done through a UNIX domain socket.
SO ANYWAY, that's why my doorbell rarely works and why you've been standing outside in the snow for five minutes.
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