How to Tail the Log of One Container in a Docker-Compose Group

docker-composeprometheus

I'm still struggling to understand why my ipmi_exporter container will not run in the same "pod" as my Prometheus, Grafana, snmp_exporter and alertmanager. When I bring up the "pod," docker-compose says ipmi_exporter has started but docker-compose ps cannot find the container. I'd like to be able to see the log containing the startup for ipmi_exporter, if that was not made clear in my post title.

Also, what is a docker-compose group of containers called? Pods are a K8s thing.

Best Answer

The docker-compose binary only commands the docker daemon. You can simply use the docker command to get what you need.

Use docker ps or docker ps -a to find out about your containers.

Use docker logs ... with container name to get logs out of a particular container. This works even if you have redirected your logs elsewhere in compose file.

Docker itself sort-of does not have a notion of a "pod". The closest you can get is to define a stack which is a collection of networks, volumes and containers - this is similar to K8s pod. Also, the stack is actually what you define in docker-compose.yml file.

Related Solutions

Docker – Check is container/service running with docker-compose

docker-compose ps -q <service_name> will display the container ID no matter it's running or not, as long as it was created.
docker ps shows only those that are actually running.

Let's combine these two commands:

if [ -z `docker ps -q --no-trunc | grep $(docker-compose ps -q <service_name>)` ]; then
  echo "No, it's not running."
else
  echo "Yes, it's running."
fi

docker ps shows short version of IDs by default, so we need to specify --no-trunc flag.

UPDATE: It threw "grep usage" warning if the service was not running. Thanks to @Dzhuneyt, here's the updated answer.

if [ -z `docker-compose ps -q <service_name>` ] || [ -z `docker ps -q --no-trunc | grep $(docker-compose ps -q <service_name>)` ]; then
  echo "No, it's not running."
else
  echo "Yes, it's running."
fi

Docker – How to forward Docker container logs to ELK

Docker compose has the logging keyword: source

logging: 
  driver: syslog
  options: 
    syslog-address: "tcp://192.168.0.42:123"

So if you know where to go from there, go for it.

If not, I can advice you to look into the gelf logging driver for docker and the logstash gelf input plugin

If you would for instance use this basic ELK-stack-in-containers setup, you would update the docker-compose file and add port - "12201:12201/udp" to logstash.

Edit the logstash.conf input section to:

input {
    tcp {
        port => 5000
    }
    gelf {
    }

}

Then configure your containers to use logging driver gelf (not syslog) and the option gelf-address=udp://ip_of_logstash:12201 (instead of syslog-address).

The only magic you will have to take care of is how Docker will find the IP address or hostname of the Logstash container. You could solve that through docker-compose naming, Docker links or just manually.

Docker and ELK are powerful, flexible, but therefore also big and complex beasts. Prepare to put in some serious time, in reading and experimentation.

Don't be afraid to open new (and preferably very specific) questions you come across while exploring all this.

Best Answer

Related Solutions

Docker – Check is container/service running with docker-compose

Docker – How to forward Docker container logs to ELK

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