Docker Container log Rotation questions

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Hi,
I have couple of containers running on el7.
The default logging driver is json.
The json log file is only one and log are getting accumulated to the file since apr.

I am in the process of creating a log rotation for it.

I created the daemon file
/etc/docker/daemon.json :

{
    "log-driver": "json-file",
    "log-opts": {
        "max-size": "10m",
        "max-file": "3"
    }
}

Added below information.

/var/lib/docker/containers/*/*.log {
        rotate 7
        daily
        compress
        missingok
        delaycompress
        copytruncate
}

I restarted the docker after making the changes.

systemctl restart docker

My Question is ,
What the prerequisite that i should do to get this done.

Should i take a back up of the running container using below command

docker save --output portal.tar dockername

What other steps that should i follow before implementing log rotate.