docker logs <C> returns nothing - docker

Question

I build and run a docker image with
docker run --detach --name api rkevinburton/myagsourceapi
But when I 'docker ps -a' I get a message that this container has exited.
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
ee956fbf1d7f rkevinburton/myagsourceapi "/bin/bash" 10 seconds ago Exited (0) 8 seconds ago api
So I want to find out why it exited. So I issue the command
docker logs ee
But this command returns nothing. As the docker host is a Windows machine I looked on ~\AppData\Local\Docker but the information in the log*.txt or install-log.* didn't seem to help me any. How can I get more information on why the container 'Exited'?

Answer 1

Docker containers exit when their main process finishes. That is why you don't get any logs.
The docker logs command batch-retrieves logs present at the time of execution.
(see: https://docs.docker.com/engine/reference/commandline/logs/)
An example:
The following will create a new container and start it:
docker run -d --name=my_test_container alpine ping -c 20 127.0.0.1
[----run----] [--------name--------] [image][-----command------]
Try to use the following, before ping command stops:
docker logs my_test_container
docker logs --follow my_test_container
The first one shows what has been printed out by ping (until then) and the second one gives you logs as ping prints out new lines.
After 20 ping requests, the ping command finishes and the container stops.
ubuntu#ubuntu:~$ docker container ls -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
e8f371000146 alpine "ping -c 20 127.0.0.1" 29 seconds ago Exited (0) 9 seconds ago my_test_container