refactor: move host-crontab generation into cron plugin
Host-crontab generation for `app.json` cron tasks now lives in the `cron` plugin, gated by a new `scheduler-uses-host-cron` trigger that the `docker-local` scheduler answers true while self-managed schedulers such as `k3s` answer false. This lets any host-cron scheduler participate in normal `app.json` cron without coupling to `scheduler-docker-local` or duplicating the crontab writer, while the `k3s` scheduler continues to manage its own in-cluster cron jobs. Closes #8862.
This commit is contained in:
Jose Diaz-Gonzalez
252
plugins/cron/crontab.go
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252
plugins/cron/crontab.go
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@@ -0,0 +1,252 @@
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package cron
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import (
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_ "embed"
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"fmt"
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"os"
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"strings"
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"text/template"
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"github.com/dokku/dokku/plugins/common"
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"golang.org/x/sync/errgroup"
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base36 "github.com/multiformats/go-base36"
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)
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//go:embed templates/cron.tmpl
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var cronTemplate string
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// usesHostCron reports whether the given scheduler writes its cron tasks to the
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// host crontab (as opposed to managing its own cron backend). An empty scheduler
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// or an unimplemented scheduler-uses-host-cron trigger is treated as false.
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func usesHostCron(scheduler string) bool {
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if scheduler == "" {
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return false
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}
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results, _ := common.CallPlugnTrigger(common.PlugnTriggerInput{
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Trigger: "scheduler-uses-host-cron",
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Args: []string{scheduler},
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})
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return results.StdoutContents() == "true"
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}
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// hostCronSchedulers returns a map keyed by every distinct scheduler seen across
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// the given apps plus the global scheduler, with a boolean value indicating
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// whether that scheduler uses the host crontab. Deduplicating up front avoids
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// redundant scheduler-uses-host-cron dispatches and any shared-cache race across
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// concurrent task collection.
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func hostCronSchedulers(appSchedulers []string) map[string]bool {
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schedulers := map[string]bool{}
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for _, scheduler := range append(appSchedulers, common.GetGlobalScheduler()) {
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if scheduler == "" {
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continue
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}
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if _, ok := schedulers[scheduler]; ok {
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continue
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}
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schedulers[scheduler] = usesHostCron(scheduler)
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}
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return schedulers
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}
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// injectedCronTasks parses the tasks injected via the cron-entries trigger for a
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// given scheduler. Each entry is newline delimited in the form
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// $SCHEDULE;$COMMAND[;$LOGFILE].
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func injectedCronTasks(scheduler string) ([]CronTask, error) {
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tasks := []CronTask{}
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response, _ := common.CallPlugnTrigger(common.PlugnTriggerInput{
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Trigger: "cron-entries",
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Args: []string{scheduler},
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})
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for _, line := range strings.Split(response.StdoutContents(), "\n") {
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if strings.TrimSpace(line) == "" {
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return []CronTask{}, nil
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}
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parts := strings.Split(line, ";")
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if len(parts) != 2 && len(parts) != 3 {
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return []CronTask{}, fmt.Errorf("Invalid injected cron task: %v", line)
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}
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id := base36.EncodeToStringLc([]byte(strings.Join(parts, ";;;")))
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task := CronTask{
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ID: id,
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Schedule: parts[0],
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AltCommand: parts[1],
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Maintenance: false,
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}
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if len(parts) == 3 {
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task.LogFile = parts[2]
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}
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tasks = append(tasks, task)
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}
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return tasks, nil
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}
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// generateCronTasks returns all cron tasks that should be written to the host
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// crontab: the app.json cron tasks for every app whose scheduler uses the host
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// crontab, plus any tasks injected via the cron-entries trigger for each such
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// scheduler. Tasks in maintenance are omitted.
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func generateCronTasks() ([]CronTask, error) {
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apps, _ := common.UnfilteredDokkuApps()
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appSchedulers := make([]string, len(apps))
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sg := new(errgroup.Group)
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for i, appName := range apps {
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i := i
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appName := appName
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sg.Go(func() error {
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appSchedulers[i] = common.GetAppScheduler(appName)
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return nil
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})
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}
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if err := sg.Wait(); err != nil {
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return []CronTask{}, err
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}
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hostCron := hostCronSchedulers(appSchedulers)
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g := new(errgroup.Group)
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results := make(chan []CronTask, len(apps)+len(hostCron))
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for i, appName := range apps {
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if !hostCron[appSchedulers[i]] {
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continue
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}
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appName := appName
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g.Go(func() error {
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c, err := FetchCronTasks(FetchCronTasksInput{AppName: appName})
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if err != nil {
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results <- []CronTask{}
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common.LogWarn(err.Error())
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return nil
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}
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results <- c
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return nil
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})
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}
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for scheduler, isHostCron := range hostCron {
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if !isHostCron {
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continue
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}
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scheduler := scheduler
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g.Go(func() error {
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tasks, err := injectedCronTasks(scheduler)
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if err != nil {
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results <- []CronTask{}
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return err
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}
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results <- tasks
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return nil
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})
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}
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err := g.Wait()
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close(results)
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tasks := []CronTask{}
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if err != nil {
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return tasks, err
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}
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for result := range results {
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for _, task := range result {
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if !task.Maintenance {
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tasks = append(tasks, task)
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}
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}
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}
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return tasks, nil
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}
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// writeCronTab regenerates the dokku user crontab from every host-cron app. It
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// is always a full regeneration, so there is no clobbering when multiple
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// schedulers use the host crontab.
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func writeCronTab() error {
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tasks, err := generateCronTasks()
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if err != nil {
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return err
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}
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if len(tasks) == 0 {
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return deleteCrontab()
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}
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mailfrom := common.PropertyGetDefault("cron", "--global", "mailfrom", DefaultProperties["mailfrom"])
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mailto := common.PropertyGetDefault("cron", "--global", "mailto", DefaultProperties["mailto"])
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data := map[string]interface{}{
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"Tasks": tasks,
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"Mailfrom": mailfrom,
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"Mailto": mailto,
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}
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t, err := getCronTemplate()
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if err != nil {
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return err
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}
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tmpFile, err := os.CreateTemp(os.TempDir(), fmt.Sprintf("dokku-%s-%s", common.MustGetEnv("DOKKU_PID"), "WriteCronTab"))
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if err != nil {
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return fmt.Errorf("Cannot create temporary schedule file: %v", err)
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}
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defer tmpFile.Close()
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defer os.Remove(tmpFile.Name())
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if err := t.Execute(tmpFile, data); err != nil {
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return fmt.Errorf("Unable to template out schedule file: %v", err)
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}
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result, err := common.CallExecCommand(common.ExecCommandInput{
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Command: "crontab",
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Args: []string{"-u", "dokku", tmpFile.Name()},
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})
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if err != nil {
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return fmt.Errorf("Unable to update schedule file: %w", err)
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}
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if result.ExitCode != 0 {
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return fmt.Errorf("Unable to update schedule file: %s", result.StderrContents())
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}
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common.LogInfo1("Updated schedule file")
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return nil
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}
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// deleteCrontab removes the dokku user crontab
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func deleteCrontab() error {
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result, err := common.CallExecCommand(common.ExecCommandInput{
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Command: "crontab",
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Args: []string{"-l", "-u", "dokku"},
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})
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if err != nil || result.ExitCode != 0 {
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return nil
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}
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result, err = common.CallExecCommand(common.ExecCommandInput{
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Command: "crontab",
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Args: []string{"-r", "-u", "dokku"},
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})
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if err != nil {
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return fmt.Errorf("Unable to remove schedule file: %w", err)
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}
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if result.ExitCode != 0 {
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return fmt.Errorf("Unable to remove schedule file: %s", result.StderrContents())
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}
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common.LogInfo1("Removed")
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return nil
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}
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// getCronTemplate parses the embedded cron template
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func getCronTemplate() (*template.Template, error) {
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t := template.New("cron")
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s := strings.TrimSpace(cronTemplate)
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return t.Parse(s)
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}
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