embedded
Edge hardware, industrial peripherals and the constraints of small machines.
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MQTT Persistent Sessions and Retained Messages for Offline Subscribers
A subscriber that drops off the network for a minute can miss every message published in that window, and a newly-connecting client sees nothing at all until the next publish. Persistent sessions and retained messages fix both, and this walks through the broker configuration and the client flags that make it work, plus a small Redis-backed cache for consumers that never speak MQTT at all.
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SMR Drives in a Replicated Cluster: Finding the Disk That Ruins the Pool
Drive-managed SMR disks report the same capacity, connector and SMART attributes as conventional drives, then fall off a latency cliff once their persistent cache is exhausted by sustained random writes. This walks through why that pattern matches exactly what a Ceph OSD does to its backing disk, and gives a reproducible benchmark that catches the problem before the disk is holding data.
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Powering and Discovering Peripherals over PoE with Multicast Announcements
Running separate power cabling to every sensor multiplies installation cost, and without some form of discovery, every new module has to be manually addressed and registered before anything can use it. This covers what Power over Ethernet actually buys you, and builds a small multicast-based announcement protocol so peripherals can be plugged in and found automatically, with a working announcer and collector you can run in two containers.
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Provisioning a Single-Board Computer as an Industrial Edge Node
Turning a bare carrier board into a working edge node is usually a manual sequence someone follows from memory, and it differs subtly between board revisions in ways the checklist never mentions. This builds an Ansible role that detects the board at runtime, loads revision-specific settings, and applies a common baseline, tested against a throwaway container so the logic can be verified without any real hardware.