minitor-go/alert.go

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