werkator/.claude/skills/architecture/SKILL.md

name, description

name	description
architecture	Detailed werkator subsystem architecture — CLI wiring and exit codes, server mode, web UI, configuration system, git access, build execution (native and Docker), watcher poll cycle, and system metrics. Use when designing or modifying code in the commands, config, git, gitea, build, artifacts, watcher, metrics, or server packages, or when a question goes beyond the overview in AGENTS.md.

werkator Architecture

werkator is a lightweight, declarative CI/CD build system. It is a dual-mode application: CLI (interactive, status, config) and Server (HTTP, persistent).

Entry Point and CLI Wiring

Spring Boot starts via WerkatorApplication. A separate CliRunner component (in the same file) implements both CommandLineRunner (runs picocli) and ExitCodeGenerator (returns the exit code). exitProcess is called only from main() via SpringApplication.exit() — never inside run(). This keeps the Spring context alive during tests.

Picocli commands are Spring @Component beans. The root command (werkatorCommand) declares subcommands as class references in @Command(subcommands = [...]). Picocli resolves them from the Spring context via the auto-configured IFactory bean.

werkatorApplication   ← @SpringBootApplication
CliRunner             ← CommandLineRunner + ExitCodeGenerator
werkatorCommand       ← root @Command, delegates to subcommands
commands/
  InitCommand         ← "init [--systemd]"
  ServerCommand       ← "server"
  StatusCommand       ← "status [--history]"
  BuildCommand        ← "build [<branch>]"
  RetryCommand        ← "retry"
  ConfigPrintCommand  ← "config:print [--full]"

status, build, and retry implement Callable<Int> for their exit codes (0 success, 1 build failure, 2 usage/config errors). build and retry run builds through the async BuildExecutor but block until completion via ConsoleBuildRunner, which streams the live log to stdout and waits for the artifact persist before the JVM exits. Branch arguments resolve legacy-style name fragments (BranchNameResolution); the CLI reuses UiFormats so console and web UI display the same formats.

The web application type is set to none in application.yml, so plain CLI runs never start a web server. The server subcommand launches a second SpringApplication with WebApplicationType.SERVLET and the server profile, then blocks until shutdown. application-server.yml switches the web type (spring.main.* properties beat programmatic builder settings), CliRunner is @Profile("!server") so the second context does not run picocli again, and the watcher poll loop starts only in the server profile (ServerWatcherLifecycle). The JSON API, artifact serving, and the web UI live in the server package; mutating endpoints are guarded by a generated control token under .git/werkator/control-token.

Web UI

The UI is server-rendered Thymeleaf (UiController, templates under src/main/resources/templates/) plus one hand-written JavaScript file (static/werkator.js) — no SPA framework, no frontend build pipeline. Pages render the full state server-side; the script then polls the JSON API and re-renders table bodies from data. Every fetch has a timeout and failures flip an explicit error badge — never re-fetch and diff whole HTML pages, and never leave a spinner without an error path (the legacy defect). Polling pauses while the tab is hidden. UiFormats/werkator.js must produce the same display formats (timestamps, durations). Two independent staleness signals, never merged: the live-indicator badge says whether this browser reaches the server, and the watcher-banner (fed from /api/watcher, in the shared nav fragment) says whether the server reaches origin — a watcher that cannot fetch leaves the server perfectly reachable and every row stale.

Configuration System

werkator is configured by two YAML files, deep-merged by ConfigLoader (later wins):

1. .werkator.yml at the repo root — committed, shared team settings.
2. .git/werkator/.werkator.yml — not committed; machine-specific overrides and secrets (git.account, git.token).

On top of those comes the branch layer: the .werkator.yml committed on a branch, applied by loadWithBranchLayer (the watcher passes the content read via git show, loadForWorktree the file in the build worktree). A branch describes its own CI and wins over both layers — the whole builds section — so a configuration can be tried out on a branch without touching other branches' builds. stripPinned removes what is not a description of this branch's build: git, server, gitea, executor, watcher, and — inside every builds definition as well as every legacy branches entry — requirePullRequest, statusContext, and docker.enabled/docker.network.

Each file is version-checked before merging (werkator.version.since/below, ConfigVersions.verdict), so the message can name the file to fix: since is hard in both directions — too old a werkator, or a file written before ConfigVersions.FORMAT_BROKE_IN and read after it — while below only warns. There is no format version (apiVersion) on purpose: only one configuration generation is supported, and the declared version exists to make the incompatibility nameable.

After merging, resolveBuildSections decides which section describes the builds: builds or the legacy branches, never both. With no real build definition (builds.maxConcurrent is not one, dropNonDefinitionBuilds already drops it) the legacy path runs and branches.default is merged into every other branch entry; otherwise branches is dropped with a warning and mergeBuildDefaults applies builds.default as the base of every other definition — its settings only, never its trigger block (TRIGGER_KEYS, a single key so that a selector added to TriggerConfig later is non-inheritable by construction). checkTriggerBlocks refuses a definition still writing onPush/atTimes/branches/activeWithin flat, per file and scoped like the version check. Deciding this on the merged map is deliberate: a build defined on a branch and unknown to the host still inherits the host's builds.default, sandbox policy included, which is what keeps the pinned keys effective for it. The result is bound to the WerkatorConfig data classes (config/werkatorConfig.kt), which define the schema and all defaults; werkatorConfig.buildSettings(branch, build) is the single answer to "what does this build run".

Three places must stay in sync when config keys change: the WerkatorConfig data classes, the commented templates generated by InitCommand, and the reference in docs/configuration.md.

Git Access

GitService shells out to the git CLI via GitCommandRunner (a thin ProcessBuilder wrapper; no JGit). Commands that need repo information take it as a constructor dependency so tests can mock it. HTTPS fetches authenticate via a temporary, secret-free GIT_ASKPASS script (GitAskPass) with credentials from config passed through environment variables.

Build Execution

BuildExecutor runs builds asynchronously: up to executor.maxConcurrent branches concurrently (default 1), but never more than one build per branch at a time. Each branch builds in its own reusable git worktree at .git/werkator/worktrees/<branchKey> (BranchWorkspaces), checked out detached at the requested commit — the primary checkout is never used for builds. Status transitions are persisted via BuildResultRepository (JSON file under .git/werkator/), published to Gitea non-fatally, and emitted as BuildStatusChangedEvents. Every run belongs to a named build definition (job, ADR 0007): the YAML builds section defines triggers (onPush, atTimes), branch selectors (branches globs, activeWithin), and build-setting overrides applied last over the merged branch config; the implicit default build (onPush, all branches) preserves the job-less behavior. Definitions are part of the branch layer — a branch may add and override its own, and they apply to that branch alone (its selectors are evaluated for it only) — while executor.maxConcurrent stays pinned. BuildResult.build records the job; restart, retry, and startup recovery re-run by that name, resolving settings from the current config. BuildResult.name — the pool, <branch>@<build> for non-default builds — keys everything display- and retention-side (repository grouping via latestPerName, retention pools, branches-view rows, permanent latest-green links), while BuildResult.branch keys everything git-side: origin lookups, gone-from-origin pruning, worktrees (every build runs in its branch's worktree, serialized per branch), and Gitea links/statuses. branches.*.autoBuild survives as a deprecated alias for a scheduled default-pool rebuild. Cancellation addresses a build by artifact key and terminates the whole process tree. Future code (watcher, server, UI) must not assume a single running build.

On context close (e.g. systemd SIGTERM), a ContextClosedEvent listener in BuildExecutor terminates the process trees of all executing builds and waits (bounded) until their results are persisted as INTERRUPTED — a shutdown is never recorded as FAILED. Builds still queued stay PENDING and start no process. Both are re-enqueued by the watcher's startup recovery; INTERRUPTED therefore publishes as Gitea state pending, not failure (GiteaStateMapping).

The runtime is selected per branch behind the BuildRunner interface: DispatchingBuildRunner (@Primary) routes to native ProcessBuildRunner (the default) or to DockerBuildRunner when branches.<name>.docker.enabled. The Docker runner shells out to the docker CLI (no SDK): it (re)builds the configured image when the Dockerfile inputs changed (tracked via the org.werkator.build-inputs-sha256 image label), maintains a per-repo Gradle cache volume, mounts the worktree and the Docker socket into a labelled (org.hoennig.werkator) --rm --init container, and repairs workspace ownership in-container after each command (under a rootless daemon the container runs as root, which is the host user, and the repair degenerates to 0:0). Git works inside the container: the primary .git is mounted read-only with .git/werkator/ masked by an empty tmpfs (credential isolation) and the worktree's admin dir mounted read-write (gitMetadataMounts). The returned Process is the attached docker run client, so log streaming and termination work exactly like native builds.

Watcher

Watcher replaces the legacy blocking main loop with a non-blocking fixed-delay poll cycle: fetch origin, enqueue due branches (changed local, recent new origin, due auto-build slots) via BuildExecutor, then prune results, artifacts, and stale worktrees. Branches whose build has requirePullRequest are enqueued only while their head commit matches a pull-request head, detected without an API token by listing refs/pull/*/head via git ls-remote (lazily, at most once per poll cycle); manual build commands bypass this gate, and watcher.pullRequestGate: false disables it globally for plain-git origins without pull-request refs. Which builds are due is decided per branch from that branch's own definitions (definitionsFor): the primary config with the branch's committed .werkator.yml merged on top, cached per branch by its head commit and the primary config it was merged with, so the git show runs only when the branch moved while an edited machine or project config still takes effect on the next poll, and falling back to the primary definitions when that config is unreadable. Nothing is scheduled until Watcher.start() is called explicitly (server/watch mode) — CLI commands and tests never start the loop. "Already built" is tracked via the result repository, not by moving local branch refs. After the enqueue decision — and only after it, because a local ref lagging behind origin is the change signal — the cycle fast-forwards the primary checkout's local branch refs to their origin counterparts (watcher.fastForwardLocalRefs, GitService.fastForwardLocalBranches), so build tools reading the shared .git from a worktree see the refs they expect; diverged or ahead branches are never touched. Auto-build slot state lives in .git/werkator/auto-builds.json; watcher health is exposed via Watcher.state().

System Metrics

SystemMetricsCollector samples CPU (/proc/stat deltas), RAM (/proc/meminfo), disk, and repository size every 60s, but only after ServerMetricsLifecycle (server profile) calls start() — like the watcher, nothing is scheduled in CLI runs or tests. Min/max/avg aggregation state persists as JSON in the artifact root (ArtifactStore.rootDir()), so restarts continue the series. Unavailable sources (e.g. no /proc outside Linux) yield null metrics served as HTTP 200 by GET /api/system — the /system page shows n/a, never an error.