Tail stdout from multiple Docker containers

Question

I have a script that starts 10 containers in background mode (fig up -d option). I want to aggregate the stdout or the log in /var/log from all of them. How can I do this?

The containers are started using different docker-compose files so I can not do docker-compose up target1 target2 target3

docker logs only accepts one container as a parameter.

I was considering creating a volume from the /var/log on all containers, mapping them to a directory outside of docker, making sure the logs do not have colliding name and than using the bash tail -f * . But I would appreciate a more elegant solution

Answer 1

This bash script will do what you want:

docker-logs

#!/bin/bash

if [ $# -eq 0 ]; then
   echo "Usage: $(basename "$0") containerid ..."
   exit 1
fi

pids=()
cleanup()
{
   kill "${pids[@]}"
}

trap cleanup EXIT

while [ $# -ne 0 ]
do
    (docker logs -f -t --tail=10 "$1"|sed -e "s/^/$1: /")&
    pids+=($!)
    shift
done
wait

Usage:

$ docker-logs containerid1 containerid2 ... containeridN

The output of this script has each line from the tracked logs prepended with the container id.

The script works in --follow mode and must be interrupted with Ctrl-C.

Note that the options of docker logs are hardcoded in the script. If you need to be able to control the options of docker logs from the command line then you will need to parse the command line arguments (for example with getopts).

Answer 2

Docker does not support as 1.12 yet. But I have a workaround via bash;

docker ps | grep -w <filter-text> | for i in `awk '{ print $1 }'`; do docker logs -f --tail=30 $i & done

I am using docker swarm modes comes with 1.12 and deploying many replication. So all of my containers contain common text which is same as service name. To tail all of its logs in a docker node , I am using this on each docker node. filter-text will be filtering only my containers.

If you want to stop tailing, this works for me;

pkill -f 'docker logs'