specify max log json file size in docker compose

Question

I am trying to specify the max file size for json-file in docker-compose.yml, like this,

log-opt:
  max-size=50m

but when I tried to docker-compose up, it threw me an error,

ERROR: In file './docker-compose.yml', service 'log-opt' must be a mapping not a string.

How to fix it?

ps. I am using docker 1.11.2

Answer 1

Your yaml syntax isn't quite correct. The documentation says it should be options not log-opt (https://docs.docker.com/compose/compose-file/#logging). Try this?

services:
    service_name:        
        logging:
            driver: "json-file"
            options:
                max-size: "50m"

You should define logging section in each one of your services not directly in root of docker-compose.

Answer 2

max-size store log files until they reach a max-size of VALUE (eg: "2048m").

Example docker-compose file config with max-size.

version: '3.2'
services:
  logstash:
    image: docker.elastic.co/logstash/logstash:7.8.0
    command:  --config.reload.automatic  
    user: savio:savio
    restart: unless-stopped
    logging:
      driver: "json-file"
      options:
        max-size: "2048m"
    ports:
      - "9600:9600" 

If you are making a change for an already running container, you need to stop and remove the container and start again.

check log settings

]# docker container inspect -f '{{.HostConfig.LogConfig}}' <ContainerName>

For more detail: link