Re:Never trust a system that seems to be working
by phkahler on Monday October 17, 2022 @12:08PM
(#33235564)
Semantics are really important in these situations. We have a system with an E-stop (emergency stop) circuit. Any break in the loop and the system will shut off. It needed to work together with one particular vendors board that insisted on having a "hardware enable" signal that it could control. Rather than adding an additional circuit, someone decided to have "hardware enable" flip a normally open relay in the E-stop circuit. Technically this "works" because enable clears the E-stop condition and allows the thing to function. From a practical point of view this has caused no end of odd problems, particularly when diagnosing issues where things fail because the meaning of this signal has been compromised.
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Re:Never trust a system that seems to be working
by oasisbob on Monday October 17, 2022 @01:56PM
(#33237357)
This reminds me of what I've seen happen with the internal health-check endpoint often added to APIs. Simple at first, but eventually there are endpoints to cause the health-check to synthetically fail for deployment purposes; the health-check is also monitoring downstream dependencies; the health-check becomes much more and much less than it was intended to be.