promtail can not parse cmd flag override configfile

[daixiang0]

Describe the bug
A clear and concise description of what the bug is.

To Reproduce
Steps to reproduce the behavior:

1. add config

# cat cmd/promtail/promtail-docker-config.yaml
server:
  http_listen_port: 9080
  grpc_listen_port: 0

positions:
  filename: /tmp/positions.yaml

clients:
  - url: http://loki:3100/api/prom/push
    batchwait: 3s <===
scrape_configs:
- job_name: system
  entry_parser: raw
  static_configs:
  - targets:
      - localhost
    labels:
      job: varlogs
      __path__: /var/log/*log

2. add value print in pkg/promtail/client/config.go and build

// UnmarshalYAML implement Yaml Unmarshaler
func (c *Config) UnmarshalYAML(unmarshal func(interface{}) error) error {
    type raw Config
    var cfg raw 
    if c.URL.URL != nil {
        // we used flags to set that value, which already has sane default.
        cfg = raw(*c)
    } else {
        // force sane defaults.
        cfg = raw{
            BackoffConfig: util.BackoffConfig{
                MaxBackoff: 5 * time.Second,
                MaxRetries: 5,
                MinBackoff: 100 * time.Millisecond,
            },
            BatchSize: 100 * 1024,
            BatchWait: 1 * time.Second,
            Timeout:   10 * time.Second,
        }
    }   

    if err := unmarshal(&cfg); err != nil {
        return err 
    }   

    *c = Config(cfg)
    fmt.Println("config yaml", c.BatchWait)
    return nil 
}

3.set config in cmd line and run

./promtail --config.file=cmd/promtail/promtail-docker-config.yaml --client.batch-wait=1s
config yaml 3s
level=warn ts=2019-05-31T09:39:25.628290877Z caller=filetargetmanager.go:101 msg="WARNING!!! entry_parser config is deprecated, please change to pipeline_stages"
level=info ts=2019-05-31T09:39:25.629777023Z caller=server.go:120 http=[::]:9080 grpc=[::]:46530 msg="server listening on addresses"

Expected behavior
cmd line config should override configfile.

Additional context:
#520
#636

[cyriltovena]

This is the expected behaviour. You need to provide the --client.url and it will work.

[daixiang0]

get it, add a comment to ensure users with no confuse about this.

[stale]

This issue has been automatically marked as stale because it has not had any activity in the past 30 days. It will be closed in 7 days if no further activity occurs. Thank you for your contributions.

[sh0rez]

Resolved this in #980