implemented 09-system-metrics.md: added system metrics: introduced system monitoring with a metrics collector, REST API endpoint, Thymeleaf UI rendering, and lifecycle management
This commit is contained in:
Michael Hoennig
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package de.hoennig.gittally.metrics
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import io.kotest.core.spec.style.FunSpec
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import io.kotest.matchers.nulls.shouldNotBeNull
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import io.kotest.matchers.shouldBe
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import java.nio.file.Files
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import java.nio.file.Path
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import java.time.Clock
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import java.time.Instant
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import java.time.ZoneOffset
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class SystemMetricsCollectorTest : FunSpec() {
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private lateinit var tempDir: Path
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private val now = Instant.parse("2026-07-07T10:00:00Z")
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private fun collector(
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cpuCount: Int = 4,
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diskSpace: (Path) -> SystemMetricsCollector.DiskSpace = { GIB_100_DISK },
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repoSizeBytes: (Path) -> Long = { HALF_GIB_BYTES },
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) = SystemMetricsCollector(
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stateFile = { tempDir.resolve("system-metrics-state.json") },
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workingDir = tempDir,
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clock = Clock.fixed(now, ZoneOffset.UTC),
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procStat = tempDir.resolve("stat"),
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procMeminfo = tempDir.resolve("meminfo"),
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cpuCount = cpuCount,
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diskSpace = diskSpace,
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repoSizeBytes = repoSizeBytes,
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)
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private fun writeStat(
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total: Long,
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idle: Long,
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) {
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// "cpu" totals across: user nice system idle iowait irq softirq steal guest guest_nice
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val user = total - idle
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Files.writeString(tempDir.resolve("stat"), "cpu $user 0 0 $idle 0 0 0 0 0 0\ncpu0 0 0 0 0 0 0 0 0 0 0\n")
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}
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private fun writeMeminfo(
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totalKib: Long,
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availableKib: Long,
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) {
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Files.writeString(
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tempDir.resolve("meminfo"),
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"MemTotal: $totalKib kB\nMemFree: 1000000 kB\nMemAvailable: $availableKib kB\n",
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)
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}
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init {
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beforeEach {
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tempDir = Files.createTempDirectory("gittally-metrics-test")
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}
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afterEach {
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tempDir.toFile().deleteRecursively()
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}
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test("CPU load is computed from /proc/stat deltas, so the first sample has no CPU metric yet") {
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writeStat(total = 1000, idle = 700)
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writeMeminfo(totalKib = 33_554_432, availableKib = 25_165_824)
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val collector = collector()
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collector.sample()
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collector.snapshot().cpuUsed shouldBe null
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writeStat(total = 1100, idle = 775)
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collector.sample()
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val snapshot = collector.snapshot()
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// 4 cores * (100 total - 75 idle) / 100 total = 1 core used
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snapshot.cpuUsed.shouldNotBeNull().current shouldBe 1.0
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snapshot.cpuIdle.shouldNotBeNull().current shouldBe 3.0
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}
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test("RAM comes from MemTotal and MemAvailable in GiB") {
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writeStat(total = 1000, idle = 700)
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writeMeminfo(totalKib = 33_554_432, availableKib = 25_165_824)
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val collector = collector()
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collector.sample()
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val snapshot = collector.snapshot()
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snapshot.ramTotalGib shouldBe 32.0
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snapshot.ramUsedGib.shouldNotBeNull().current shouldBe 8.0
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snapshot.ramFreeGib.shouldNotBeNull().current shouldBe 24.0
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}
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test("disk and repository size are reported in GiB") {
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writeStat(total = 1000, idle = 700)
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writeMeminfo(totalKib = 33_554_432, availableKib = 25_165_824)
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val collector = collector()
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collector.sample()
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val snapshot = collector.snapshot()
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snapshot.diskTotalGib shouldBe 100.0
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snapshot.diskUsedGib.shouldNotBeNull().current shouldBe 40.0
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snapshot.diskFreeGib.shouldNotBeNull().current shouldBe 55.0
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snapshot.repoSizeGib.shouldNotBeNull().current shouldBe 0.5
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}
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test("min, max, and avg aggregate over all samples") {
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writeStat(total = 1000, idle = 700)
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writeMeminfo(totalKib = 33_554_432, availableKib = 25_165_824)
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val usedGibValues = mutableListOf(40L, 20L, 60L)
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val collector =
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collector(diskSpace = {
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SystemMetricsCollector.DiskSpace(
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totalBytes = 100L * GIB,
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usedBytes = usedGibValues.removeFirst() * GIB,
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freeBytes = 30L * GIB,
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)
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})
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repeat(3) { collector.sample() }
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val diskUsed = collector.snapshot().diskUsedGib.shouldNotBeNull()
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diskUsed.current shouldBe 60.0
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diskUsed.min shouldBe 20.0
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diskUsed.max shouldBe 60.0
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diskUsed.avg shouldBe 40.0
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}
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test("a restart loads the persisted aggregation state and continues the series") {
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writeStat(total = 1000, idle = 700)
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writeMeminfo(totalKib = 33_554_432, availableKib = 25_165_824)
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collector(repoSizeBytes = { 4L * GIB }).sample()
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val restarted = collector(repoSizeBytes = { 2L * GIB })
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restarted.sample()
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val snapshot = restarted.snapshot()
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snapshot.sampleCount shouldBe 2
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val repoSize = snapshot.repoSizeGib.shouldNotBeNull()
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repoSize.current shouldBe 2.0
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repoSize.min shouldBe 2.0
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repoSize.max shouldBe 4.0
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repoSize.avg shouldBe 3.0
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}
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test("a corrupt state file starts a fresh series instead of failing") {
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writeStat(total = 1000, idle = 700)
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writeMeminfo(totalKib = 33_554_432, availableKib = 25_165_824)
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Files.writeString(tempDir.resolve("system-metrics-state.json"), "not json {")
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val collector = collector()
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collector.sample()
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collector.snapshot().sampleCount shouldBe 1
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}
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test("unreadable sources degrade to null metrics, never fail the sample") {
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// no stat/meminfo files written, disk and repo-size probes fail
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val collector =
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collector(
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diskSpace = { error("no file store") },
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repoSizeBytes = { error("walk failed") },
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)
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collector.sample()
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val snapshot = collector.snapshot()
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snapshot.timestamp shouldBe now
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snapshot.sampleCount shouldBe 1
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snapshot.cpuCount shouldBe 4
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snapshot.cpuUsed shouldBe null
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snapshot.ramTotalGib shouldBe null
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snapshot.ramUsedGib shouldBe null
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snapshot.diskTotalGib shouldBe null
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snapshot.diskUsedGib shouldBe null
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snapshot.repoSizeGib shouldBe null
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}
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test("the repository size probe is throttled to every 10th sample") {
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writeStat(total = 1000, idle = 700)
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writeMeminfo(totalKib = 33_554_432, availableKib = 25_165_824)
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var probes = 0
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val collector =
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collector(repoSizeBytes = {
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probes++
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HALF_GIB_BYTES
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})
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repeat(11) { collector.sample() }
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probes shouldBe 2
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collector
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.snapshot()
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.repoSizeGib
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.shouldNotBeNull()
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.current shouldBe 0.5
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}
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test("the snapshot before the first sample is empty but well-formed") {
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val snapshot = collector().snapshot()
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snapshot.timestamp shouldBe null
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snapshot.sampleCount shouldBe 0
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snapshot.cpuCount shouldBe 4
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snapshot.cpuUsed shouldBe null
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}
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}
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companion object {
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private const val GIB = 1_073_741_824L
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private const val HALF_GIB_BYTES = GIB / 2
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private val GIB_100_DISK =
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SystemMetricsCollector.DiskSpace(
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totalBytes = 100L * GIB,
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usedBytes = 40L * GIB,
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freeBytes = 55L * GIB,
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)
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}
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}
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