How to output logs in a containerized application? - go

Question

Normally, in docker/k8s, it's recommended that directly ouput the logs to the stdout.
Then we can use kubectl logs or docker logs to see the logs.
like: time=123 action=write msg=hello world , as a tty, it might be colorized for human friendliness.
However, if we want to export the logs to a log processing center, like EFK (elasticsearch-fluentd-kibana), we need a json-format log file.
like: {"time"=123,"action"="write","msg"="hello world"}
What I want?
Is there a log method that can take into account both human friendliness and json format?
I'm looking for a way that if I use docker logs, then I can get human-readable logs, and at the same time, the log collector can still get the logs in json-format
Conclusion
Thanks for the answer below. I have got 2 methods:
different log format in different env:
1.1 use text-format in developing: docker logs will print colorized and human readable logs.
1.2 use json-format in production: EFK can process json-format well.
log collector's format convertion
2.1 we use text-format, but in log collector like fluentd we can define some scripts to translate text-format kv pair to json-format kv pair.

Answer 1

Kubernetes has such option of structured logging for its system components.
Klog library allows to use --logging-format=json flag that enables to change the format of logs to JSON output - more information about it here and here.

Answer 2

yes you can do that with Flunetd, below are the basic action items that you need to take to finalize this setup
Configure docker container to log to stdout (you can use any format you like)
Configure FluentD to tail docker files from /var/lib/docker/containers/*/*-json.log
parse logs with Flunetd and change the format to JSON logs
output the logs to Elasticsearch.
This article shows exactly how to do this setup also this one explain how to parse Key-Value logs