Wiki: CI

CI: what a push queues

• What a build can reach
  • Measured on bay1
• The table

Three mechanisms decide what a push does to CI, and they interact:

• Dedupe. A job's result is a property of the commit's tree. A commit that already has a passed, queued or running build for a job is not queued again; a commit whose tree already passed a job gets that result as its status, naming the build it came from (#177). Only a trusted build counts, and for tree reuse only one on the image the job names: a fork's green build does not stand for the repository's own, so its commit is built again when it lands on a branch (#258). A job that names no image: is compared as naming none: its reuse does not notice the runner's default image changing, because reuse is decided when the push is queued, before any runner claims the build, and runners can differ in their default. Name the image in ci.yml to tie reuse to it; after an operator changes a runner's -image, build trigger builds a job afresh, since a triggered build is never reused. When a trusted and an untrusted build of the same commit both run, the one that finishes last sets ci/<job> on that commit. A failed, cancelled or abandoned build does not count: that commit runs again.
• Path filters. paths and paths-ignore on a job are evaluated against the files the push changed. The diff base is the old tip when it is an ancestor of the new one, and the merge base with the default branch otherwise: a new branch, or a force push after a rebase (#176). A filter that cannot be evaluated, because there is no diff base or the diff fails, runs the job rather than skipping it. A filter that excludes the push records a skipped status, which require-checks accepts (#172).
• The reaper. A build a runner claimed and never reported is failed by the scheduler's tick: two minutes after its log stream ended, or at the build deadline if no stream was ever seen (#179). Its status reads build abandoned.

Which runner takes a build is the fourth: a build is claimed only by a runner attached to its repository (or one polling with a full-scope admin key), and an untrusted build only by one started with -untrusted. A repository with no runner attached queues builds nothing claims. See the Users page. Among what a runner may claim it takes the oldest pending build, across every repository it serves; a repository that must never wait on another gets a runner of its own (decided in krz/gitbay#207). There is no cap on how many builds an account queues or how often a schedule fires, and none is planned (krz/gitbay#206): a tick queues nothing while the job's last build is pending or running, so a repository with no runner holds one row per scheduled job, and a schedule with a runner attached spends its owner's compute, not the instance's.

Scheduled jobs run on their cron against the default branch, never on push; a default-branch push registers or updates them. Tag jobs run on a matching tag push and nothing else.

A running build is followed with build log <owner/name> <n> --follow: the stored log, then output as the runner sends it, then the outcome as build <n> <status> on stderr once the build ends. The exit code is 0 whatever the outcome. A follow of a build still queued after ten minutes ends on its own and says so on stderr, since nothing reaps a queued build. The build page does the same without JavaScript while a build is queued or running; ?follow=0 renders it once. An account holds at most eight follows open, and signed-out viewers share one account's eight. Over the JSON API the command answers when the build ends, with the whole log. Read access is checked again every two seconds: a follower who loses it is told the repository is not found. A restart ends every open follow with a message saying so, rather than holding the drain; follow again once the daemon is back.

A failed build names the step it stopped at: the log's last line reads step 3/3 failed: exit 1, and build show prints failed step (3/3 go test ./... (exit 1)) and duration. build log <owner/name> <n> --step failed prints only that step's output, --step 2 another one (0 is the clone before the first step), and --tail 40 the last forty lines of whichever was chosen; neither combines with --follow. The build page folds the finished log into one section per step, opens the failed one and links to it from the top as "Jump to failure". Builds from before this reported no step; their last section is taken as the failed one.

jobs:
  plain:
    steps: [echo plain]
  onapp:
    paths: [app/**]
    steps: [echo onapp]
  notapp:
    paths-ignore: [app/**]
    steps: [echo notapp]
  nightly:
    schedule: "0 3 * * *"
    steps: [echo nightly]
  release:
    tags: "v*"
    steps: [echo release]