How to remove date-time and tag from Fluentd logs?

Question

I'm trying to use Fluentd as a central logging service for my docker containers setup.

I use Fluent golang client to write logs from the application https://github.com/fluent/fluent-logger-golang

I post log line like this from the application

logger, _ := fluent.New(fluent.Config{FluentPort: 24224, FluentHost: "fluentd"})
defer logger.Close()
tag := "web"
var data = map[string]string{
    "foo":  "bar",
    "hoge": "hoge",
}
error := logger.Post(tag, data)

Fluentd conf file

 <source>
  @type  forward
  @id    app_logs
  @label @mainstream
  port  24224
</source>

<label @mainstream>
  <match **>
    @type  file
    @id    app_logs
    path   /fluentd/log/app.log
    append true
  </match>
</label>

The log appears as below in the file

2020-09-23T00:05:06+00:00   web {"foo":"bar","hoge":"hoge"}

I don't want to see timestamp and the tag added before the log line. How can I remove it?

Answer 1

What you seeing is @type stdout. Fluentd prints timestamp and tag to stdout for debugging purposes. If you replace this with any other output - @type file or @type s3 and format json, it will serialize the data into valid json without this prefix. Example: https://docs.fluentd.org/output/file#less-than-format-greater-than-directive