I use bitnami fluentd chart for Kubernetes and my setup is almost native besides of some changes.

My source section looks like

            @type tail
            path /var/log/containers/*my-app*.log
            pos_file /opt/bitnami/fluentd/logs/buffers/fluentd-docker.pos
            tag kubernetes.*
            read_from_head true

and my application sends to stdout some more advanced logs information like:

2021-07-13 11:33:49.060 +0000 - [ERROR] - fatal error - play.api.http.DefaultHttpErrorHandler in postman-akka.actor.default-dispatcher-6 play.api.UnexpectedException: Unexpected exception[RuntimeException: java.net.ConnectException: Connection refused (Connection refused)]
	at play.api.http.HttpErrorHandlerExceptions$.throwableToUsefulException(HttpErrorHandler.scala:328)
	at play.api.http.DefaultHttpErrorHandler.onServerError(HttpErrorHandler 

and the problem is because in fluentd forwarder I can see (in /var/log/containers/*) that all records are stored in the following format:

{"log":"2021-07-13 19:54:48.523 +0000 - [ERROR] - from akka.io.TcpListener in postman-akka.actor.default-dispatcher-6 New connection accepted \n","stream":"stdout","time":"2021-07-13T19:54:48.523724149Z"}
{"log":"2021-07-13 19:54:48.523 +0000 - [ERROR] -- play.api.http.DefaultHttpErrorHandler in postman-akka.actor.default-dispatcher-6  \n","stream":"stdout","time":"2021-07-13T19:55:10.479279395Z"} 
{"log":"2021-07-13 19:54:48.523 +0000 - [ERROR] - play.api.UnexpectedException: Unexpected exception[RuntimeException: }
{"log":"2021-07-13 19:54:48.523 +0000 - [ERROR] - java.net.ConnectException: Connection refused (Connection refused)] }

and the problem as you can see here is that all those lines are "separated" log record.

I would like to extract entire log message with entire stack trace, I wrote some configuration to fluentd parse section

              @type regexp
              expression /^(?<time>^(.*?:.*?)):\d\d.\d+\s\+0000 - (?<type>(\[\w+\])).- (?<text>(.*))/m
              time_key time
              time_format %Y-%m-%d %H:%M:%S
            </parse>

but I am pretty sure that this is not problem because from some reason those files in (/var/log/containers/*.log) already storing wrong format of records, how can I configure fluentd forwarder to "take" logs from containers and store logs in format (non-json) ?