lightning: setting --log-file "-" will not print any log to stdout

[fengou1]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

1. create a tidb cloud cluster
2. import some data into cluster
3. check Loki/ES by cluster ID and orgID
4. lightning log been truncated

DBaaS run lightning by parameter: --log-file="-", issue can be reproduced in 5.3.0 env.

2. What did you expect to see? (Required)

After DBaaS import data done, Loki/ES shall able to show all lightning log.

3. What did you see instead (Required)

Loki/ES only show part of lightning log at very begin of lightning start.

4. What is your TiDB version? (Required)

/tmp # /tidb-lightning -V
Release Version: v5.3.0
Git Commit Hash: c83f032b04a40b3148dff712392dd924ae064132
Git Branch: heads/refs/tags/v5.3.0
Go Version: go1.16.4
UTC Build Time: 2021-11-16 11:54:51
Race Enabled: false

[kennytm]

this bug is introduced by #29291, which skips initializing logger when the log file is set to empty.

tidb/br/pkg/lightning/lightning.go

Lines 77 to 82 in 34bd98d

	func initEnv(cfg *config.GlobalConfig) error {
	if cfg.App.Config.File == "" {
	return nil
	}
	return log.InitLogger(&cfg.App.Config, cfg.TiDB.LogLevel)
	}

[github-actions]

Please check whether the issue should be labeled with 'affects-x.y' or 'fixes-x.y.z', and then remove 'needs-more-info' label.