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Tools & Reviews articles

2 published
SRShashank Rawlani
Tools & Reviews

Test Cron Schedules by Their Fire Times, Not Their Strings

Reviewing a five-field string cannot tell you when a job runs: the two day fields are combined with OR in cron but AND in systemd, the spring gap deletes a run and the autumn fold duplicates one, and Kubernetes then decides separately whether a matched run may start. This shows you how to compute fire times from a pinned base time using the parser your scheduler actually vendors — robfig/cron for CronJobs, systemd-analyze calendar --base-time for timers — and how startingDeadlineSeconds, concurrencyPolicy and the 100-missed-schedule ceiling interact. It ends with the evidence to keep: the cronjob-scheduled-timestamp annotation diffed against actual start times, so a run that never happened shows up as a gap.

15 min read
Dark technical illustration of two schedule timelines running edge to edge. The upper lane shows wall-clock fire times as a row of green ticks hanging from a rule; at one highlighted transition column a tick is missing, drawn as a dashed outline with a crossed-out circle above it, and at a second transition column a single slot carries two overlapping orange ticks ringed together. Curved droppers connect every wall-clock tick to the lower lane, where the same schedule in UTC is a perfectly even row of green ticks with no gap and no duplicate, the fold's two instants landing as separate ringed nodes. A strip of small cells along the bottom repeats the pattern, one cell empty and one doubled.
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