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monitoring

  • Measure at the percentile that hurts

    Note1 min read

    A mean response time of 180ms is compatible with 5% of requests taking four seconds, and it is the 5% who write in. The average is the one…

  • MEMORY USAGE tells you which key is the problem

    Note1 min read

    –bigkeys reports the largest key by element count, which is not the same as the largest by memory — a hash with 500 short fields is smaller than…

  • Logging drivers, and why json-file fills the disk

    Note1 min read

    The default driver writes every line to a JSON file with no rotation, so a chatty container quietly consumes the host disk and nothing points at it —…

  • Compose file version 3, and what swarm changed

    Deep dive10 min read

    v3 exists to be deployable to a scheduler, and that removes things a single-host file relied on. What went, why it had to, and what replaces it.

  • Object cache misses are invisible without instrumentation

    Note2 min read

    A persistent object cache either works or silently does not, and both look identical from the front end: the site is up, the pages render, and the queries…

  • Designing an API two mobile clients can live with

    Deep dive14 min read

    Two apps, two release cycles, and neither can be forced to update. What is additive, what is not, and the decisions that have to be made before the…

  • Backups that are restored on a schedule

    Note1 min read

    A backup job exiting zero proves the job ran. Truncated dumps, a mysqldump that hit a lock and gave up, and an archive of an empty directory all…

  • Centralised logging that answers a question

    Deep dive17 min read

    Four servers, eleven log files, and an incident reconstructed from three of them. Shipping first and parsing second, structured events, and the correlation id that makes it useful.

  • Every threshold needs a duration

    Note2 min read

    An alert on an instantaneous value fires on the spike that a deploy, a cron job or a single slow request produces, so the first thing anyone does…

  • The runbook link belongs in the alert

    Note1 min read

    An alert saying HighErrorRate on shop-web at three in the morning is a puzzle. The person receiving it may not have written the check, and the context lives…