minitor-go/monitor.go

package main

import (
	"math"
	"os/exec"
	"time"

	"git.iamthefij.com/iamthefij/slog"
)

// Monitor represents a particular periodic check of a command
type Monitor struct { //nolint:maligned
	// Config values
	CheckIntervalStr *string `hcl:"check_interval,optional"`
	CheckInterval    time.Duration

	Name         string   `hcl:"name,label"`
	AlertAfter   int      `hcl:"alert_after,optional"`
	AlertEvery   *int     `hcl:"alert_every,optional"`
	AlertDown    []string `hcl:"alert_down,optional"`
	AlertUp      []string `hcl:"alert_up,optional"`
	Command      []string `hcl:"command,optional"`
	ShellCommand string   `hcl:"shell_command,optional"`

	// Other values
	alertCount        int
	failureCount      int
	lastCheck         time.Time
	lastSuccess       time.Time
	lastOutput        string
	lastCheckDuration time.Duration
}

// IsValid returns a boolean indicating if the Monitor has been correctly
// configured
func (monitor Monitor) IsValid() bool {
	// TODO: Refactor and return an error containing more information on what was invalid
	hasCommand := len(monitor.Command) > 0
	hasShellCommand := monitor.ShellCommand != ""
	hasValidAlertAfter := monitor.AlertAfter > 0
	hasAlertDown := len(monitor.AlertDown) > 0

	hasAtLeastOneCommand := hasCommand || hasShellCommand
	hasAtMostOneCommand := !(hasCommand && hasShellCommand)

	return hasAtLeastOneCommand &&
		hasAtMostOneCommand &&
		hasValidAlertAfter &&
		hasAlertDown
}

func (monitor Monitor) LastOutput() string {
	return monitor.lastOutput
}

// ShouldCheck returns a boolean indicating if the Monitor is ready to be
// be checked again
func (monitor Monitor) ShouldCheck() bool {
	if monitor.lastCheck.IsZero() || monitor.CheckInterval == 0 {
		return true
	}

	sinceLastCheck := time.Since(monitor.lastCheck)

	return sinceLastCheck >= monitor.CheckInterval
}

// Check will run the command configured by the Monitor and return a status
// and a possible AlertNotice
func (monitor *Monitor) Check() (bool, *AlertNotice) {
	var cmd *exec.Cmd
	if len(monitor.Command) > 0 {
		cmd = exec.Command(monitor.Command[0], monitor.Command[1:]...)
	} else if monitor.ShellCommand != "" {
		cmd = ShellCommand(monitor.ShellCommand)
	} else {
		slog.Fatalf("Monitor %s has no command configured", monitor.Name)
	}

	checkStartTime := time.Now()
	output, err := cmd.CombinedOutput()
	monitor.lastCheck = time.Now()
	monitor.lastOutput = string(output)
	monitor.lastCheckDuration = monitor.lastCheck.Sub(checkStartTime)

	var alertNotice *AlertNotice

	isSuccess := (err == nil)
	if isSuccess {
		alertNotice = monitor.success()
	} else {
		alertNotice = monitor.failure()
	}

	slog.Debugf("Command output: %s", monitor.lastOutput)
	slog.OnErrWarnf(err, "Command result: %v", err)

	slog.Infof(
		"%s success=%t, alert=%t",
		monitor.Name,
		isSuccess,
		alertNotice != nil,
	)

	return isSuccess, alertNotice
}

// IsUp returns the status of the current monitor
func (monitor Monitor) IsUp() bool {
	return monitor.alertCount == 0
}

// LastCheckMilliseconds gives number of miliseconds the last check ran for
func (monitor Monitor) LastCheckMilliseconds() int64 {
	return monitor.lastCheckDuration.Milliseconds()
}

func (monitor *Monitor) success() (notice *AlertNotice) {
	if !monitor.IsUp() {
		// Alert that we have recovered
		notice = monitor.createAlertNotice(true)
	}

	monitor.failureCount = 0
	monitor.alertCount = 0
	monitor.lastSuccess = time.Now()

	return
}

func (monitor *Monitor) failure() (notice *AlertNotice) {
	monitor.failureCount++
	// If we haven't hit the minimum failures, we can exit
	if monitor.failureCount < monitor.AlertAfter {
		slog.Debugf(
			"%s failed but did not hit minimum failures. "+
				"Count: %v alert after: %v",
			monitor.Name,
			monitor.failureCount,
			monitor.AlertAfter,
		)

		return
	}

	// Take number of failures after minimum
	failureCount := (monitor.failureCount - monitor.AlertAfter)

	// Use alert cadence to determine if we should alert
	switch {
	case monitor.AlertEvery == nil, *monitor.AlertEvery == 0:
		// Handle alerting on first failure only
		if failureCount == 0 {
			notice = monitor.createAlertNotice(false)
		}
	case *monitor.AlertEvery > 0:
		// Handle integer number of failures before alerting
		if failureCount%*monitor.AlertEvery == 0 {
			notice = monitor.createAlertNotice(false)
		}
	default:
		// Handle negative numbers indicating an exponential backoff
		if failureCount >= int(math.Pow(2, float64(monitor.alertCount))-1) { //nolint:gomnd
			notice = monitor.createAlertNotice(false)
		}
	}

	// If we're going to alert, increment count
	if notice != nil {
		monitor.alertCount++
	}

	return notice
}

// GetAlertNames gives a list of alert names for a given monitor status
func (monitor Monitor) GetAlertNames(up bool) []string {
	if up {
		return monitor.AlertUp
	}

	return monitor.AlertDown
}

func (monitor Monitor) createAlertNotice(isUp bool) *AlertNotice {
	// TODO: Maybe add something about recovery status here
	return &AlertNotice{
		MonitorName:     monitor.Name,
		AlertCount:      monitor.alertCount,
		FailureCount:    monitor.failureCount,
		LastCheckOutput: monitor.lastOutput,
		LastSuccess:     monitor.lastSuccess,
		IsUp:            isUp,
	}
}