init

.gitea/workflows/build.yml

@@ -0,0 +1,36 @@
+name: Build heartbeat
+
+on:
+  push:
+    branches: [main]
+    paths:
+      - '**/*.go'
+      - 'go.mod'
+      - 'go.sum'
+      - '.gitea/workflows/build.yml'
+  workflow_dispatch:
+
+jobs:
+  build:
+    runs-on: ubuntu-24.04
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Setup Go
+        uses: actions/setup-go@v5
+        with:
+          go-version: '1.22'
+          cache: true
+
+      - name: Build binary
+        run: |
+          CGO_ENABLED=0 GOOS=linux GOARCH=amd64 go build -trimpath -ldflags="-s -w" -o heartbeat ./cmd/heartbeat
+
+      - name: Upload artifact
+        uses: actions/upload-artifact@v4
+        with:
+          name: heartbeat-linux-amd64
+          path: heartbeat
+          retention-days: 365

.gitignore

@@ -0,0 +1,22 @@
+# built binary
+/heartbeat
+
+# runtime config (contains webhook URL)
+/config.yaml
+
+# Go build cache and test artifacts
+*.test
+*.out
+/vendor/
+
+# OS
+.DS_Store
+Thumbs.db
+
+# Editor
+.vscode/
+.idea/
+*.swp
+*.swo
+*~
+

cmd/heartbeat/main.go

@@ -0,0 +1,34 @@
+package main
+
+import (
+	"context"
+	"flag"
+	"log"
+	"os/signal"
+	"syscall"
+
+	"heartbeat/internal/app"
+	"heartbeat/internal/config"
+)
+
+func main() {
+	configPath := flag.String("config", "./config.yaml", "Path to config file")
+	flag.Parse()
+
+	cfg, err := config.Load(*configPath)
+	if err != nil {
+		log.Fatalf("load config: %v", err)
+	}
+
+	runner, err := app.New(cfg)
+	if err != nil {
+		log.Fatalf("initialize app: %v", err)
+	}
+
+	ctx, stop := signal.NotifyContext(context.Background(), syscall.SIGINT, syscall.SIGTERM)
+	defer stop()
+
+	if err := runner.Run(ctx); err != nil {
+		log.Fatalf("run heartbeat: %v", err)
+	}
+}

config.example.yaml

@@ -0,0 +1,33 @@
+server_name: s1
+discord_webhook_url: https://discord.com/api/webhooks/replace/me
+notify_role_id: "1500565629390819479"
+
+sample_interval: 1m
+summary_interval: 6h
+request_timeout: 10s
+
+thresholds:
+  disk_used_percent_warning: 85
+  disk_used_percent_critical: 93
+  free_gb_warning: 20
+  free_gb_critical: 10
+  inode_used_percent_warning: 85
+  inode_used_percent_critical: 93
+  memory_used_percent_warning: 90
+  memory_used_percent_critical: 97
+  swap_used_percent_warning: 25
+  swap_used_percent_critical: 50
+  cpu_avg_15m_warning: 80
+  cpu_avg_15m_critical: 95
+  cpu_avg_12h_warning: 65
+  cpu_avg_12h_critical: 85
+  load_per_core_warning: 0.9
+  load_per_core_critical: 1.25
+  process_count_warning: 350
+  process_count_critical: 500
+
+sites:
+  - name: pismen.com
+    url: https://pismen.com
+    expected_status: 200
+    timeout: 10s

go.mod

@@ -0,0 +1,19 @@
+module heartbeat
+
+go 1.22.0
+
+require (
+	github.com/shirou/gopsutil/v3 v3.24.5
+	gopkg.in/yaml.v3 v3.0.1
+)
+
+require (
+	github.com/go-ole/go-ole v1.2.6 // indirect
+	github.com/lufia/plan9stats v0.0.0-20211012122336-39d0f177ccd0 // indirect
+	github.com/power-devops/perfstat v0.0.0-20210106213030-5aafc221ea8c // indirect
+	github.com/shoenig/go-m1cpu v0.1.6 // indirect
+	github.com/tklauser/go-sysconf v0.3.12 // indirect
+	github.com/tklauser/numcpus v0.6.1 // indirect
+	github.com/yusufpapurcu/wmi v1.2.4 // indirect
+	golang.org/x/sys v0.20.0 // indirect
+)

go.sum

@@ -0,0 +1,38 @@
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/go-ole/go-ole v1.2.6 h1:/Fpf6oFPoeFik9ty7siob0G6Ke8QvQEuVcuChpwXzpY=
+github.com/go-ole/go-ole v1.2.6/go.mod h1:pprOEPIfldk/42T2oK7lQ4v4JSDwmV0As9GaiUsvbm0=
+github.com/google/go-cmp v0.5.6/go.mod h1:v8dTdLbMG2kIc/vJvl+f65V22dbkXbowE6jgT/gNBxE=
+github.com/google/go-cmp v0.6.0 h1:ofyhxvXcZhMsU5ulbFiLKl/XBFqE1GSq7atu8tAmTRI=
+github.com/google/go-cmp v0.6.0/go.mod h1:17dUlkBOakJ0+DkrSSNjCkIjxS6bF9zb3elmeNGIjoY=
+github.com/lufia/plan9stats v0.0.0-20211012122336-39d0f177ccd0 h1:6E+4a0GO5zZEnZ81pIr0yLvtUWk2if982qA3F3QD6H4=
+github.com/lufia/plan9stats v0.0.0-20211012122336-39d0f177ccd0/go.mod h1:zJYVVT2jmtg6P3p1VtQj7WsuWi/y4VnjVBn7F8KPB3I=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/power-devops/perfstat v0.0.0-20210106213030-5aafc221ea8c h1:ncq/mPwQF4JjgDlrVEn3C11VoGHZN7m8qihwgMEtzYw=
+github.com/power-devops/perfstat v0.0.0-20210106213030-5aafc221ea8c/go.mod h1:OmDBASR4679mdNQnz2pUhc2G8CO2JrUAVFDRBDP/hJE=
+github.com/shirou/gopsutil/v3 v3.24.5 h1:i0t8kL+kQTvpAYToeuiVk3TgDeKOFioZO3Ztz/iZ9pI=
+github.com/shirou/gopsutil/v3 v3.24.5/go.mod h1:bsoOS1aStSs9ErQ1WWfxllSeS1K5D+U30r2NfcubMVk=
+github.com/shoenig/go-m1cpu v0.1.6 h1:nxdKQNcEB6vzgA2E2bvzKIYRuNj7XNJ4S/aRSwKzFtM=
+github.com/shoenig/go-m1cpu v0.1.6/go.mod h1:1JJMcUBvfNwpq05QDQVAnx3gUHr9IYF7GNg9SUEw2VQ=
+github.com/shoenig/test v0.6.4 h1:kVTaSd7WLz5WZ2IaoM0RSzRsUD+m8wRR+5qvntpn4LU=
+github.com/shoenig/test v0.6.4/go.mod h1:byHiCGXqrVaflBLAMq/srcZIHynQPQgeyvkvXnjqq0k=
+github.com/stretchr/testify v1.9.0 h1:HtqpIVDClZ4nwg75+f6Lvsy/wHu+3BoSGCbBAcpTsTg=
+github.com/stretchr/testify v1.9.0/go.mod h1:r2ic/lqez/lEtzL7wO/rwa5dbSLXVDPFyf8C91i36aY=
+github.com/tklauser/go-sysconf v0.3.12 h1:0QaGUFOdQaIVdPgfITYzaTegZvdCjmYO52cSFAEVmqU=
+github.com/tklauser/go-sysconf v0.3.12/go.mod h1:Ho14jnntGE1fpdOqQEEaiKRpvIavV0hSfmBq8nJbHYI=
+github.com/tklauser/numcpus v0.6.1 h1:ng9scYS7az0Bk4OZLvrNXNSAO2Pxr1XXRAPyjhIx+Fk=
+github.com/tklauser/numcpus v0.6.1/go.mod h1:1XfjsgE2zo8GVw7POkMbHENHzVg3GzmoZ9fESEdAacY=
+github.com/yusufpapurcu/wmi v1.2.4 h1:zFUKzehAFReQwLys1b/iSMl+JQGSCSjtVqQn9bBrPo0=
+github.com/yusufpapurcu/wmi v1.2.4/go.mod h1:SBZ9tNy3G9/m5Oi98Zks0QjeHVDvuK0qfxQmPyzfmi0=
+golang.org/x/sys v0.0.0-20190916202348-b4ddaad3f8a3/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/sys v0.0.0-20201204225414-ed752295db88/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/sys v0.8.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/sys v0.11.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/sys v0.20.0 h1:Od9JTbYCk261bKm4M/mw7AklTlFYIa0bIp9BgSm1S8Y=
+golang.org/x/sys v0.20.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
+golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
+gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=

heartbeat.service

@@ -0,0 +1,14 @@
+[Unit]
+Description=heartbeat server monitor
+After=network-online.target
+Wants=network-online.target
+
+[Service]
+User=root
+WorkingDirectory=/opt/heartbeat
+ExecStart=/opt/heartbeat/heartbeat --config /opt/heartbeat/config.yaml
+Restart=always
+RestartSec=5
+
+[Install]
+WantedBy=multi-user.target

internal/alerts/alerts.go

@@ -0,0 +1,130 @@
+package alerts
+
+import (
+	"fmt"
+	"sort"
+	"strings"
+	"time"
+
+	"heartbeat/internal/config"
+	"heartbeat/internal/metrics"
+)
+
+type Severity string
+
+const (
+	SeverityHealthy  Severity = "healthy"
+	SeverityWarning  Severity = "warning"
+	SeverityCritical Severity = "critical"
+)
+
+type Event struct {
+	Key      string
+	Severity Severity
+	Title    string
+	Body     string
+}
+
+type Evaluator struct {
+	states map[string]Severity
+}
+
+func NewEvaluator() *Evaluator {
+	return &Evaluator{states: make(map[string]Severity)}
+}
+
+func (e *Evaluator) Evaluate(cfg config.Config, sample metrics.Sample) []Event {
+	events := []Event{}
+	events = append(events, e.metricEvent("disk_used", compareHigh(sample.RootUsedPercent, cfg.Thresholds.DiskUsedPercentWarning, cfg.Thresholds.DiskUsedPercentCritical), fmt.Sprintf("Root disk usage %.1f%%", sample.RootUsedPercent), fmt.Sprintf("Root partition is %.1f%% used with %.1f GB free.", sample.RootUsedPercent, sample.RootFreeGB))...)
+	events = append(events, e.metricEvent("free_gb", compareLow(sample.RootFreeGB, cfg.Thresholds.FreeGBWarning, cfg.Thresholds.FreeGBCritical), fmt.Sprintf("Low disk space %.1f GB", sample.RootFreeGB), fmt.Sprintf("Root partition free space is %.1f GB.", sample.RootFreeGB))...)
+	events = append(events, e.metricEvent("inode_used", compareHigh(sample.InodeUsedPercent, cfg.Thresholds.InodeUsedPercentWarning, cfg.Thresholds.InodeUsedPercentCritical), fmt.Sprintf("Inode usage %.1f%%", sample.InodeUsedPercent), fmt.Sprintf("Root partition inode usage is %.1f%%.", sample.InodeUsedPercent))...)
+	events = append(events, e.metricEvent("memory_used", compareHigh(sample.MemoryUsedPercent, cfg.Thresholds.MemoryUsedPercentWarning, cfg.Thresholds.MemoryUsedPercentCritical), fmt.Sprintf("Memory usage %.1f%%", sample.MemoryUsedPercent), fmt.Sprintf("Memory usage is %.1f%%.", sample.MemoryUsedPercent))...)
+	events = append(events, e.metricEvent("swap_used", compareHigh(sample.SwapUsedPercent, cfg.Thresholds.SwapUsedPercentWarning, cfg.Thresholds.SwapUsedPercentCritical), fmt.Sprintf("Swap usage %.1f%%", sample.SwapUsedPercent), fmt.Sprintf("Swap usage is %.1f%%.", sample.SwapUsedPercent))...)
+	events = append(events, e.metricEvent("cpu_avg_15m", compareHigh(sample.CPUAvg15mPercent, cfg.Thresholds.CPUAvg15mWarning, cfg.Thresholds.CPUAvg15mCritical), fmt.Sprintf("CPU 15m average %.1f%%", sample.CPUAvg15mPercent), fmt.Sprintf("CPU rolling 15-minute average is %.1f%%.", sample.CPUAvg15mPercent))...)
+	events = append(events, e.metricEvent("cpu_avg_12h", compareHigh(sample.CPUAvg12hPercent, cfg.Thresholds.CPUAvg12hWarning, cfg.Thresholds.CPUAvg12hCritical), fmt.Sprintf("CPU 12h average %.1f%%", sample.CPUAvg12hPercent), fmt.Sprintf("CPU rolling 12-hour average is %.1f%%.", sample.CPUAvg12hPercent))...)
+	events = append(events, e.metricEvent("load_per_core", compareHigh(sample.LoadPerCore, cfg.Thresholds.LoadPerCoreWarning, cfg.Thresholds.LoadPerCoreCritical), fmt.Sprintf("Load per core %.2f", sample.LoadPerCore), fmt.Sprintf("15-minute load per core is %.2f.", sample.LoadPerCore))...)
+	events = append(events, e.metricEvent("process_count", compareHigh(float64(sample.ProcessCount), float64(cfg.Thresholds.ProcessCountWarning), float64(cfg.Thresholds.ProcessCountCritical)), fmt.Sprintf("Process count %d", sample.ProcessCount), fmt.Sprintf("Process count is %d.", sample.ProcessCount))...)
+	for _, site := range sample.Sites {
+		severity := SeverityHealthy
+		if !site.Healthy {
+			severity = SeverityCritical
+		}
+		title := fmt.Sprintf("Site %s reachable", site.Name)
+		body := fmt.Sprintf("%s responded with %d in %s.", site.URL, site.StatusCode, site.Latency.Round(time.Millisecond))
+		if !site.Healthy {
+			title = fmt.Sprintf("Site %s failed", site.Name)
+			body = fmt.Sprintf("%s check failed: %s.", site.URL, site.ErrorMessage)
+		}
+		events = append(events, e.metricEvent("site:"+site.Name, severity, title, body)...)
+	}
+	sort.Slice(events, func(i, j int) bool { return events[i].Key < events[j].Key })
+	return events
+}
+
+func (e *Evaluator) metricEvent(key string, severity Severity, title string, body string) []Event {
+	previous := e.states[key]
+	if previous == "" {
+		e.states[key] = severity
+		if severity == SeverityHealthy {
+			return nil
+		}
+		return []Event{{Key: key, Severity: severity, Title: title, Body: body}}
+	}
+	if previous == severity {
+		return nil
+	}
+	e.states[key] = severity
+	if severity == SeverityHealthy {
+		return []Event{{Key: key, Severity: severity, Title: recoveryTitle(title), Body: body}}
+	}
+	return []Event{{Key: key, Severity: severity, Title: title, Body: body}}
+}
+
+func recoveryTitle(title string) string {
+	return "Recovered: " + title
+}
+
+func compareHigh(value float64, warning float64, critical float64) Severity {
+	switch {
+	case critical > 0 && value >= critical:
+		return SeverityCritical
+	case warning > 0 && value >= warning:
+		return SeverityWarning
+	default:
+		return SeverityHealthy
+	}
+}
+
+func compareLow(value float64, warning float64, critical float64) Severity {
+	switch {
+	case critical > 0 && value <= critical:
+		return SeverityCritical
+	case warning > 0 && value <= warning:
+		return SeverityWarning
+	default:
+		return SeverityHealthy
+	}
+}
+
+func FormatSummary(sample metrics.Sample) string {
+	lines := []string{
+		fmt.Sprintf("CPU now %.1f%% | 15m %.1f%% | 12h %.1f%%", sample.CPUCurrentPercent, sample.CPUAvg15mPercent, sample.CPUAvg12hPercent),
+		fmt.Sprintf("Memory %.1f%% | Swap %.1f%%", sample.MemoryUsedPercent, sample.SwapUsedPercent),
+		fmt.Sprintf("Disk / %.1f%% used | %.1f GB free | Inodes %.1f%%", sample.RootUsedPercent, sample.RootFreeGB, sample.InodeUsedPercent),
+		fmt.Sprintf("Load %.2f / %.2f / %.2f | Per core %.2f", sample.Load1, sample.Load5, sample.Load15, sample.LoadPerCore),
+		fmt.Sprintf("Network RX %.1f KB/s | TX %.1f KB/s", sample.RXBytesPerSecond/1024, sample.TXBytesPerSecond/1024),
+		fmt.Sprintf("Processes %d | Hosted sites %d", sample.ProcessCount, sample.HostedServiceCount),
+	}
+	siteStates := make([]string, 0, len(sample.Sites))
+	for _, site := range sample.Sites {
+		state := "up"
+		if !site.Healthy {
+			state = "down"
+		}
+		siteStates = append(siteStates, fmt.Sprintf("%s=%s", site.Name, state))
+	}
+	if len(siteStates) > 0 {
+		lines = append(lines, "Sites "+strings.Join(siteStates, ", "))
+	}
+	return strings.Join(lines, "\n")
+}

internal/app/app.go

@@ -0,0 +1,82 @@
+package app
+
+import (
+	"context"
+	"log"
+	"time"
+
+	"heartbeat/internal/alerts"
+	"heartbeat/internal/config"
+	"heartbeat/internal/discord"
+	"heartbeat/internal/metrics"
+)
+
+type Runner struct {
+	cfg       config.Config
+	sampler   *metrics.Sampler
+	evaluator *alerts.Evaluator
+	discord   *discord.Client
+}
+
+func New(cfg config.Config) (*Runner, error) {
+	return &Runner{
+		cfg:       cfg,
+		sampler:   metrics.NewSampler(cfg.RequestTimeout),
+		evaluator: alerts.NewEvaluator(),
+		discord:   discord.New(cfg.ServerName, cfg.DiscordWebhookURL, cfg.NotifyRoleID, cfg.RequestTimeout),
+	}, nil
+}
+
+func (r *Runner) Run(ctx context.Context) error {
+	if err := r.tick(ctx, true); err != nil {
+		log.Printf("initial tick failed: %v", err)
+	}
+
+	sampleTicker := time.NewTicker(r.cfg.SampleInterval)
+	defer sampleTicker.Stop()
+
+	summaryTicker := time.NewTicker(r.cfg.SummaryInterval)
+	defer summaryTicker.Stop()
+
+	for {
+		select {
+		case <-ctx.Done():
+			return nil
+		case <-sampleTicker.C:
+			if err := r.tick(ctx, false); err != nil {
+				log.Printf("sample tick failed: %v", err)
+			}
+		case <-summaryTicker.C:
+			if err := r.sendSummary(ctx); err != nil {
+				log.Printf("summary failed: %v", err)
+			}
+		}
+	}
+}
+
+func (r *Runner) tick(ctx context.Context, sendSummary bool) error {
+	sample, err := r.sampler.Collect(ctx, r.cfg)
+	if err != nil {
+		return err
+	}
+	if sendSummary {
+		if err := r.discord.SendSummary(ctx, sample, r.cfg.SummaryInterval); err != nil {
+			log.Printf("summary send failed: %v", err)
+		}
+	}
+	for _, event := range r.evaluator.Evaluate(r.cfg, sample) {
+		if err := r.discord.SendEvent(ctx, sample, event); err != nil {
+			log.Printf("event send failed for %s: %v", event.Key, err)
+		}
+	}
+	return nil
+}
+
+func (r *Runner) sendSummary(ctx context.Context) error {
+	sample, err := r.sampler.Collect(ctx, r.cfg)
+	if err != nil {
+		return err
+	}
+	return r.discord.SendSummary(ctx, sample, r.cfg.SummaryInterval)
+}
+

internal/config/config.go

@@ -0,0 +1,117 @@
+package config
+
+import (
+	"fmt"
+	"os"
+	"time"
+
+	"gopkg.in/yaml.v3"
+)
+
+type Config struct {
+	ServerName        string        `yaml:"server_name"`
+	DiscordWebhookURL string        `yaml:"discord_webhook_url"`
+	NotifyRoleID      string        `yaml:"notify_role_id"`
+	SampleInterval    time.Duration `yaml:"sample_interval"`
+	SummaryInterval   time.Duration `yaml:"summary_interval"`
+	RequestTimeout    time.Duration `yaml:"request_timeout"`
+	Thresholds        Thresholds    `yaml:"thresholds"`
+	Sites             []Site        `yaml:"sites"`
+}
+
+type Thresholds struct {
+	DiskUsedPercentWarning  float64 `yaml:"disk_used_percent_warning"`
+	DiskUsedPercentCritical float64 `yaml:"disk_used_percent_critical"`
+	FreeGBWarning           float64 `yaml:"free_gb_warning"`
+	FreeGBCritical          float64 `yaml:"free_gb_critical"`
+	InodeUsedPercentWarning float64 `yaml:"inode_used_percent_warning"`
+	InodeUsedPercentCritical float64 `yaml:"inode_used_percent_critical"`
+	MemoryUsedPercentWarning float64 `yaml:"memory_used_percent_warning"`
+	MemoryUsedPercentCritical float64 `yaml:"memory_used_percent_critical"`
+	SwapUsedPercentWarning   float64 `yaml:"swap_used_percent_warning"`
+	SwapUsedPercentCritical  float64 `yaml:"swap_used_percent_critical"`
+	CPUAvg15mWarning        float64 `yaml:"cpu_avg_15m_warning"`
+	CPUAvg15mCritical       float64 `yaml:"cpu_avg_15m_critical"`
+	CPUAvg12hWarning        float64 `yaml:"cpu_avg_12h_warning"`
+	CPUAvg12hCritical       float64 `yaml:"cpu_avg_12h_critical"`
+	LoadPerCoreWarning      float64 `yaml:"load_per_core_warning"`
+	LoadPerCoreCritical     float64 `yaml:"load_per_core_critical"`
+	ProcessCountWarning     int     `yaml:"process_count_warning"`
+	ProcessCountCritical    int     `yaml:"process_count_critical"`
+}
+
+type Site struct {
+	Name           string        `yaml:"name"`
+	URL            string        `yaml:"url"`
+	ExpectedStatus int           `yaml:"expected_status"`
+	Timeout        time.Duration `yaml:"timeout"`
+}
+
+func Load(path string) (Config, error) {
+	data, err := os.ReadFile(path)
+	if err != nil {
+		return Config{}, err
+	}
+
+	var cfg Config
+	if err := yaml.Unmarshal(data, &cfg); err != nil {
+		return Config{}, err
+	}
+
+	applyDefaults(&cfg)
+	if err := cfg.Validate(); err != nil {
+		return Config{}, err
+	}
+
+	return cfg, nil
+}
+
+func applyDefaults(cfg *Config) {
+	if cfg.SampleInterval == 0 {
+		cfg.SampleInterval = time.Minute
+	}
+	if cfg.SummaryInterval == 0 {
+		cfg.SummaryInterval = 6 * time.Hour
+	}
+	if cfg.RequestTimeout == 0 {
+		cfg.RequestTimeout = 10 * time.Second
+	}
+	for index := range cfg.Sites {
+		if cfg.Sites[index].ExpectedStatus == 0 {
+			cfg.Sites[index].ExpectedStatus = 200
+		}
+		if cfg.Sites[index].Timeout == 0 {
+			cfg.Sites[index].Timeout = cfg.RequestTimeout
+		}
+	}
+	if cfg.Thresholds.ProcessCountWarning == 0 {
+		cfg.Thresholds.ProcessCountWarning = 350
+	}
+	if cfg.Thresholds.ProcessCountCritical == 0 {
+		cfg.Thresholds.ProcessCountCritical = 500
+	}
+}
+
+func (cfg Config) Validate() error {
+	if cfg.ServerName == "" {
+		return fmt.Errorf("server_name is required")
+	}
+	if cfg.DiscordWebhookURL == "" {
+		return fmt.Errorf("discord_webhook_url is required")
+	}
+	if cfg.SampleInterval <= 0 {
+		return fmt.Errorf("sample_interval must be > 0")
+	}
+	if cfg.SummaryInterval <= 0 {
+		return fmt.Errorf("summary_interval must be > 0")
+	}
+	for _, site := range cfg.Sites {
+		if site.Name == "" {
+			return fmt.Errorf("site name is required")
+		}
+		if site.URL == "" {
+			return fmt.Errorf("site URL is required for %s", site.Name)
+		}
+	}
+	return nil
+}

internal/discord/discord.go

@@ -0,0 +1,201 @@
+package discord
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"strings"
+	"time"
+
+	"heartbeat/internal/alerts"
+	"heartbeat/internal/metrics"
+)
+
+type Client struct {
+	webhookURL string
+	httpClient *http.Client
+	serverName string
+	notifyRoleID string
+}
+
+type webhookPayload struct {
+	Content         string          `json:"content,omitempty"`
+	AllowedMentions allowedMentions `json:"allowed_mentions,omitempty"`
+	Embeds          []embed         `json:"embeds"`
+}
+
+type allowedMentions struct {
+	Roles []string `json:"roles,omitempty"`
+}
+
+type embed struct {
+	Title       string      `json:"title"`
+	Description string      `json:"description,omitempty"`
+	Color       int         `json:"color"`
+	Timestamp   string      `json:"timestamp,omitempty"`
+	Fields      []embedField `json:"fields,omitempty"`
+	Footer      *embedFooter `json:"footer,omitempty"`
+}
+
+type embedField struct {
+	Name   string `json:"name"`
+	Value  string `json:"value"`
+	Inline bool   `json:"inline"`
+}
+
+type embedFooter struct {
+	Text string `json:"text"`
+}
+
+func New(serverName string, webhookURL string, notifyRoleID string, timeout time.Duration) *Client {
+	return &Client{
+		serverName: serverName,
+		webhookURL: webhookURL,
+		httpClient: &http.Client{Timeout: timeout},
+		notifyRoleID: notifyRoleID,
+	}
+}
+
+func (c *Client) SendSummary(ctx context.Context, sample metrics.Sample, summaryInterval time.Duration) error {
+	fields := []embedField{
+		{Name: "Server", Value: c.serverName, Inline: true},
+		{Name: "Generated", Value: formatSummaryTime(sample.Timestamp), Inline: true},
+		{Name: "Uptime", Value: formatUptime(sample.UptimeSeconds), Inline: true},
+		{Name: "CPU", Value: fmt.Sprintf("Now: %.1f%%\n15m: %.1f%%\n12h: %.1f%%", sample.CPUCurrentPercent, sample.CPUAvg15mPercent, sample.CPUAvg12hPercent), Inline: true},
+		{Name: "Load", Value: fmt.Sprintf("1m: %.2f\n5m: %.2f\n15m/core: %.2f", sample.Load1, sample.Load5, sample.LoadPerCore), Inline: true},
+		{Name: "Memory", Value: fmt.Sprintf("RAM: %.1f%%\nSwap: %.1f%%", sample.MemoryUsedPercent, sample.SwapUsedPercent), Inline: true},
+		{Name: "Disk /", Value: fmt.Sprintf("Used: %.1f%%\nFree: %.1f GB\nInodes: %.1f%%", sample.RootUsedPercent, sample.RootFreeGB, sample.InodeUsedPercent), Inline: true},
+		{Name: "Network", Value: fmt.Sprintf("RX: %s\nTX: %s", formatRate(sample.RXBytesPerSecond), formatRate(sample.TXBytesPerSecond)), Inline: true},
+		{Name: "Processes", Value: fmt.Sprintf("Count: %d", sample.ProcessCount), Inline: true},
+		{Name: "Sites", Value: formatSiteStatuses(sample.Sites), Inline: false},
+	}
+	return c.send(ctx, webhookPayload{Embeds: []embed{{
+		Title:       fmt.Sprintf("heartbeat (%s) - %s", formatSummaryIntervalHours(summaryInterval), c.serverName),
+		Description: "Scheduled server health snapshot.",
+		Color:       0x2D9CDB,
+		Fields:      fields,
+		Footer:      &embedFooter{Text: formatSummaryFooter(c.serverName)},
+	}}})
+}
+
+func (c *Client) SendEvent(ctx context.Context, sample metrics.Sample, event alerts.Event) error {
+	fields := []embedField{
+		{Name: "Server", Value: c.serverName, Inline: true},
+		{Name: "Severity", Value: string(event.Severity), Inline: true},
+		{Name: "Timestamp", Value: formatEventTime(sample.Timestamp), Inline: true},
+	}
+	payload := webhookPayload{Embeds: []embed{{
+		Title:       event.Title,
+		Description: event.Body,
+		Color:       colorForSeverity(event.Severity),
+		Timestamp:   sample.Timestamp.Format(time.RFC3339),
+		Fields:      fields,
+	}}}
+	if c.notifyRoleID != "" && (event.Severity == alerts.SeverityWarning || event.Severity == alerts.SeverityCritical) {
+		payload.Content = fmt.Sprintf("<@&%s>", c.notifyRoleID)
+		payload.AllowedMentions = allowedMentions{Roles: []string{c.notifyRoleID}}
+	}
+	return c.send(ctx, payload)
+}
+
+func formatUptime(totalSeconds uint64) string {
+	duration := time.Duration(totalSeconds) * time.Second
+	days := duration / (24 * time.Hour)
+	duration -= days * 24 * time.Hour
+	hours := duration / time.Hour
+	duration -= hours * time.Hour
+	minutes := duration / time.Minute
+	if days > 0 {
+		return fmt.Sprintf("%dd %dh %dm", days, hours, minutes)
+	}
+	return fmt.Sprintf("%dh %dm", hours, minutes)
+}
+
+func formatSiteStatuses(sites []metrics.SiteStatus) string {
+	if len(sites) == 0 {
+		return "No site checks configured"
+	}
+	parts := make([]string, 0, len(sites))
+	for _, site := range sites {
+		status := "UP"
+		detail := fmt.Sprintf("%d in %s", site.StatusCode, site.Latency.Round(time.Millisecond))
+		if !site.Healthy {
+			status = "DOWN"
+			detail = site.ErrorMessage
+		}
+		parts = append(parts, fmt.Sprintf("%s: %s (%s)", site.Name, status, detail))
+	}
+	return strings.Join(parts, "\n")
+}
+
+func formatSummaryTime(timestamp time.Time) string {
+	unixSeconds := timestamp.Unix()
+	return fmt.Sprintf("<t:%d:f>", unixSeconds)
+}
+
+func formatEventTime(timestamp time.Time) string {
+	unixSeconds := timestamp.Unix()
+	return fmt.Sprintf("<t:%d:f> - <t:%d:R>", unixSeconds, unixSeconds)
+}
+
+func formatSummaryFooter(serverName string) string {
+	return fmt.Sprintf("heartbeat - %s", serverName)
+}
+
+func formatSummaryIntervalHours(interval time.Duration) string {
+	if interval%time.Hour == 0 {
+		return fmt.Sprintf("%dh", interval/time.Hour)
+	}
+	return fmt.Sprintf("%.2fh", interval.Hours())
+}
+
+func formatRate(bytesPerSecond float64) string {
+	if bytesPerSecond < 0 {
+		return "n/a"
+	}
+	if bytesPerSecond < 1024 {
+		return fmt.Sprintf("%.0f B/s", bytesPerSecond)
+	}
+	kib := bytesPerSecond / 1024
+	if kib < 1024 {
+		return fmt.Sprintf("%.2f KB/s", kib)
+	}
+	mib := kib / 1024
+	return fmt.Sprintf("%.2f MB/s", mib)
+}
+
+func (c *Client) send(ctx context.Context, payload webhookPayload) error {
+	buffer := &bytes.Buffer{}
+	if err := json.NewEncoder(buffer).Encode(payload); err != nil {
+		return err
+	}
+
+	req, err := http.NewRequestWithContext(ctx, http.MethodPost, c.webhookURL, buffer)
+	if err != nil {
+		return err
+	}
+	req.Header.Set("Content-Type", "application/json")
+
+	resp, err := c.httpClient.Do(req)
+	if err != nil {
+		return err
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
+		return fmt.Errorf("discord webhook returned %s", resp.Status)
+	}
+	return nil
+}
+
+func colorForSeverity(severity alerts.Severity) int {
+	switch severity {
+	case alerts.SeverityCritical:
+		return 0xE74C3C
+	case alerts.SeverityWarning:
+		return 0xF39C12
+	default:
+		return 0x27AE60
+	}
+}

internal/metrics/metrics.go

@@ -0,0 +1,261 @@
+package metrics
+
+import (
+	"context"
+	"fmt"
+	"net"
+	"net/http"
+	"strings"
+	"time"
+
+	"heartbeat/internal/config"
+
+	"github.com/shirou/gopsutil/v3/cpu"
+	"github.com/shirou/gopsutil/v3/disk"
+	"github.com/shirou/gopsutil/v3/host"
+	"github.com/shirou/gopsutil/v3/load"
+	"github.com/shirou/gopsutil/v3/mem"
+	gnet "github.com/shirou/gopsutil/v3/net"
+	"github.com/shirou/gopsutil/v3/process"
+)
+
+const gib = 1024 * 1024 * 1024
+
+type Sample struct {
+	Timestamp          time.Time
+	RootUsedPercent    float64
+	RootFreeGB         float64
+	InodeUsedPercent   float64
+	CPUCurrentPercent  float64
+	CPUAvg15mPercent   float64
+	CPUAvg12hPercent   float64
+	MemoryUsedPercent  float64
+	SwapUsedPercent    float64
+	Load1              float64
+	Load5              float64
+	Load15             float64
+	LoadPerCore        float64
+	RXBytesPerSecond   float64
+	TXBytesPerSecond   float64
+	ProcessCount       int
+	HostedServiceCount int
+	UptimeSeconds      uint64
+	Sites              []SiteStatus
+}
+
+type SiteStatus struct {
+	Name           string
+	URL            string
+	Healthy        bool
+	StatusCode     int
+	Latency        time.Duration
+	ErrorMessage   string
+	ExpectedStatus int
+}
+
+type Sampler struct {
+	httpClient *http.Client
+	prevNet    netIO
+	history    []historyPoint
+	historyCap int
+}
+
+type netIO struct {
+	timestamp time.Time
+	rx        uint64
+	tx        uint64
+}
+
+type historyPoint struct {
+	timestamp time.Time
+	cpu       float64
+}
+
+func NewSampler(timeout time.Duration) *Sampler {
+	transport := &http.Transport{
+		Proxy: http.ProxyFromEnvironment,
+		DialContext: (&net.Dialer{
+			Timeout: timeout,
+		}).DialContext,
+		TLSHandshakeTimeout: timeout,
+	}
+
+	return &Sampler{
+		httpClient: &http.Client{Timeout: timeout, Transport: transport},
+		historyCap: 12 * 60,
+	}
+}
+
+func (s *Sampler) Collect(ctx context.Context, cfg config.Config) (Sample, error) {
+	now := time.Now().UTC()
+
+	rootUsage, err := disk.UsageWithContext(ctx, "/")
+	if err != nil {
+		return Sample{}, fmt.Errorf("root usage: %w", err)
+	}
+
+	cpuPercents, err := cpu.PercentWithContext(ctx, time.Second, false)
+	if err != nil {
+		return Sample{}, fmt.Errorf("cpu percent: %w", err)
+	}
+
+	virtualMemory, err := mem.VirtualMemoryWithContext(ctx)
+	if err != nil {
+		return Sample{}, fmt.Errorf("memory: %w", err)
+	}
+
+	swapMemory, err := mem.SwapMemoryWithContext(ctx)
+	if err != nil {
+		return Sample{}, fmt.Errorf("swap: %w", err)
+	}
+
+	avg, err := load.AvgWithContext(ctx)
+	if err != nil {
+		return Sample{}, fmt.Errorf("load average: %w", err)
+	}
+
+	hostInfo, err := host.InfoWithContext(ctx)
+	if err != nil {
+		return Sample{}, fmt.Errorf("host info: %w", err)
+	}
+
+	processes, err := process.ProcessesWithContext(ctx)
+	if err != nil {
+		return Sample{}, fmt.Errorf("process list: %w", err)
+	}
+
+	rxRate, txRate := s.networkRates(ctx, now)
+	sites := s.checkSites(ctx, cfg.Sites)
+
+	currentCPU := 0.0
+	if len(cpuPercents) > 0 {
+		currentCPU = cpuPercents[0]
+	}
+
+	s.appendHistory(now, currentCPU)
+	coreCount, err := cpu.CountsWithContext(ctx, true)
+	if err != nil || coreCount == 0 {
+		coreCount = 1
+	}
+
+	return Sample{
+		Timestamp:          now,
+		RootUsedPercent:    rootUsage.UsedPercent,
+		RootFreeGB:         float64(rootUsage.Free) / gib,
+		InodeUsedPercent:   inodeUsedPercent(rootUsage),
+		CPUCurrentPercent:  currentCPU,
+		CPUAvg15mPercent:   s.averageCPU(15 * time.Minute),
+		CPUAvg12hPercent:   s.averageCPU(12 * time.Hour),
+		MemoryUsedPercent:  virtualMemory.UsedPercent,
+		SwapUsedPercent:    swapMemory.UsedPercent,
+		Load1:              avg.Load1,
+		Load5:              avg.Load5,
+		Load15:             avg.Load15,
+		LoadPerCore:        avg.Load15 / float64(coreCount),
+		RXBytesPerSecond:   rxRate,
+		TXBytesPerSecond:   txRate,
+		ProcessCount:       len(processes),
+		HostedServiceCount: len(cfg.Sites),
+		UptimeSeconds:      hostInfo.Uptime,
+		Sites:              sites,
+	}, nil
+}
+
+func (s *Sampler) appendHistory(timestamp time.Time, cpuPercent float64) {
+	s.history = append(s.history, historyPoint{timestamp: timestamp, cpu: cpuPercent})
+	if len(s.history) > s.historyCap {
+		s.history = s.history[len(s.history)-s.historyCap:]
+	}
+}
+
+func (s *Sampler) averageCPU(window time.Duration) float64 {
+	if len(s.history) == 0 {
+		return 0
+	}
+	cutoff := time.Now().UTC().Add(-window)
+	total := 0.0
+	count := 0.0
+	for _, point := range s.history {
+		if point.timestamp.Before(cutoff) {
+			continue
+		}
+		total += point.cpu
+		count++
+	}
+	if count == 0 {
+		return 0
+	}
+	return total / count
+}
+
+func (s *Sampler) networkRates(ctx context.Context, now time.Time) (float64, float64) {
+	stats, err := gnet.IOCountersWithContext(ctx, false)
+	if err != nil || len(stats) == 0 {
+		return 0, 0
+	}
+	current := netIO{timestamp: now, rx: stats[0].BytesRecv, tx: stats[0].BytesSent}
+	if s.prevNet.timestamp.IsZero() {
+		s.prevNet = current
+		return 0, 0
+	}
+	seconds := current.timestamp.Sub(s.prevNet.timestamp).Seconds()
+	if seconds <= 0 {
+		return 0, 0
+	}
+	rxRate := float64(current.rx-s.prevNet.rx) / seconds
+	txRate := float64(current.tx-s.prevNet.tx) / seconds
+	s.prevNet = current
+	return rxRate, txRate
+}
+
+func (s *Sampler) checkSites(ctx context.Context, sites []config.Site) []SiteStatus {
+	results := make([]SiteStatus, 0, len(sites))
+	for _, site := range sites {
+		results = append(results, s.checkSite(ctx, site))
+	}
+	return results
+}
+
+func (s *Sampler) checkSite(parent context.Context, site config.Site) SiteStatus {
+	ctx, cancel := context.WithTimeout(parent, site.Timeout)
+	defer cancel()
+
+	start := time.Now()
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, site.URL, nil)
+	if err != nil {
+		return SiteStatus{Name: site.Name, URL: site.URL, ExpectedStatus: site.ExpectedStatus, ErrorMessage: err.Error()}
+	}
+
+	resp, err := s.httpClient.Do(req)
+	if err != nil {
+		return SiteStatus{Name: site.Name, URL: site.URL, ExpectedStatus: site.ExpectedStatus, ErrorMessage: normalizeError(err)}
+	}
+	defer resp.Body.Close()
+
+	status := SiteStatus{
+		Name:           site.Name,
+		URL:            site.URL,
+		Healthy:        resp.StatusCode == site.ExpectedStatus,
+		StatusCode:     resp.StatusCode,
+		Latency:        time.Since(start),
+		ExpectedStatus: site.ExpectedStatus,
+	}
+	if !status.Healthy {
+		status.ErrorMessage = fmt.Sprintf("expected %d, got %d", site.ExpectedStatus, resp.StatusCode)
+	}
+	return status
+}
+
+func normalizeError(err error) string {
+	message := err.Error()
+	message = strings.TrimPrefix(message, "Get ")
+	return message
+}
+
+func inodeUsedPercent(stat *disk.UsageStat) float64 {
+	if stat.InodesTotal == 0 {
+		return 0
+	}
+	used := stat.InodesTotal - stat.InodesFree
+	return float64(used) / float64(stat.InodesTotal) * 100
+}