A minimal monitoring tool
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package main
import (
"bytes"
"errors"
"fmt"
"os/exec"
"strings"
"text/template"
"time"
"git.iamthefij.com/iamthefij/slog"
)
var (
errNoTemplate = errors.New("no template")
// ErrAlertFailed indicates that an alert failed to send
ErrAlertFailed = errors.New("alert failed")
)
// Alert is a config driven mechanism for sending a notice
type Alert struct {
Name string
Command CommandOrShell
commandTemplate []*template.Template
commandShellTemplate *template.Template
}
// AlertNotice captures the context for an alert to be sent
type AlertNotice struct {
AlertCount int16
FailureCount int16
IsUp bool
LastSuccess time.Time
MonitorName string
LastCheckOutput string
}
// IsValid returns a boolean indicating if the Alert has been correctly
// configured
func (alert Alert) IsValid() bool {
return !alert.Command.Empty()
}
// BuildTemplates compiles command templates for the Alert
func (alert *Alert) BuildTemplates() error {
// TODO: Remove legacy template support later after 1.0
legacy := strings.NewReplacer(
"{alert_count}", "{{.AlertCount}}",
"{alert_message}", "{{.MonitorName}} check has failed {{.FailureCount}} times",
"{failure_count}", "{{.FailureCount}}",
"{last_output}", "{{.LastCheckOutput}}",
"{last_success}", "{{.LastSuccess}}",
"{monitor_name}", "{{.MonitorName}}",
)
slog.Debugf("Building template for alert %s", alert.Name)
switch {
case alert.commandTemplate == nil && alert.Command.Command != nil:
alert.commandTemplate = []*template.Template{}
for i, cmdPart := range alert.Command.Command {
if PyCompat {
cmdPart = legacy.Replace(cmdPart)
}
alert.commandTemplate = append(alert.commandTemplate, template.Must(
template.New(alert.Name+fmt.Sprint(i)).Parse(cmdPart),
))
}
case alert.commandShellTemplate == nil && alert.Command.ShellCommand != "":
shellCmd := alert.Command.ShellCommand
if PyCompat {
shellCmd = legacy.Replace(shellCmd)
}
alert.commandShellTemplate = template.Must(
template.New(alert.Name).Parse(shellCmd),
)
default:
return fmt.Errorf("No template provided for alert %s: %w", alert.Name, errNoTemplate)
}
return nil
}
// Send will send an alert notice by executing the command template
func (alert Alert) Send(notice AlertNotice) (outputStr string, err error) {
slog.Infof("Sending alert %s for %s", alert.Name, notice.MonitorName)
var cmd *exec.Cmd
switch {
case alert.commandTemplate != nil:
command := []string{}
for _, cmdTmp := range alert.commandTemplate {
var commandBuffer bytes.Buffer
err = cmdTmp.Execute(&commandBuffer, notice)
if err != nil {
return
}
command = append(command, commandBuffer.String())
}
cmd = exec.Command(command[0], command[1:]...)
case alert.commandShellTemplate != nil:
var commandBuffer bytes.Buffer
err = alert.commandShellTemplate.Execute(&commandBuffer, notice)
if err != nil {
return
}
shellCommand := commandBuffer.String()
cmd = ShellCommand(shellCommand)
default:
err = fmt.Errorf("No templates compiled for alert %s: %w", alert.Name, errNoTemplate)
return
}
// Exit if we're not ready to run the command
if cmd == nil || err != nil {
return
}
var output []byte
output, err = cmd.CombinedOutput()
outputStr = string(output)
slog.Debugf("Alert output for: %s\n---\n%s\n---", alert.Name, outputStr)
if err != nil {
err = fmt.Errorf(
"Alert '%s' failed to send. Returned %v: %w",
alert.Name,
err,
ErrAlertFailed,
)
}
return outputStr, err
}
// NewLogAlert creates an alert that does basic logging using echo
func NewLogAlert() *Alert {
return &Alert{
Name: "log",
Command: CommandOrShell{
Command: []string{
"echo",
"{{.MonitorName}} {{if .IsUp}}has recovered{{else}}check has failed {{.FailureCount}} times{{end}}",
},
},
}
}