Docker Compose keep container running

Question

I want to start a service with docker-compose and keep the container running so I can get its IP-address via 'docker inspect'. However, the container always exits right after starting up.

I tried to add "command: ["sleep", "60"]" and other things to the docker-compose.yml but whenever I add the line with "command:..." I cant call "docker-compose up" as I will get the message "Cannot start container ..... System error: invalid character 'k' looking for beginning of value"

I also tried adding "CMD sleep 60" and whatnot to the Dockerfile itself but these commands do not seem to be executed.

Is there an easy way to keep the container alive or to fix one of my problems?

EDIT: Here is the Compose file I want to run:

version: '2'
services:
  my-test:
    image: ubuntu
    command: bash -c "while true; do echo hello; sleep 2; done"

It's working fine If I start this with docker-compose under OS X, but if I try the same under Ubuntu 16.04 it gives me above error message.

If I try the approach with the Dockerfile, the Dockerfile looks like this:

FROM ubuntu:latest
CMD ["sleep", "60"]

Which does not seem to do anything

EDIT 2: I have to correct myself, turned out it was the same problem with the Dockerfile and the docker-compose.yml: Each time I add either "CMD ..." to the Dockerfile OR add "command ..." to the compose file, I get above error with the invalid character. If I remove both commands, it works flawlessly.

Answer 1

To keep a container running when you start it with docker-compose, use the following command

command: tail -F anything

In the above command the last part anything should be included literally, and the assumption is that such a file is not present in the container, but with the -F option (capital -F not to be confused with -f which in contrast will terminate immediateley if the file is not found) the tail command will wait forever for the file anything to appear. A forever waiting process is basically what we need.

So your docker-compose.yml becomes

version: '2'
services:
  my-test:
    image: ubuntu
    command: tail -F anything

and you can run a shell to get into the container using the following command

docker exec -i -t composename_my-test_1 bash

where composename is the name that docker-compose prepends to your containers.

Answer 2

You can use tty configuration option.

version: '3'

services:
  app:
    image: node:8
    tty: true           # <-- This option

Note: If you use Dockerfile for image and CMD in Dockerfile, this option won't work; however, you can use the entrypoint option in the compose file which clears the CMD from the Dockerfile.

Answer 3

Based on the comment of @aanand on GitHub Aug 26, 2015, one could use tail -f /dev/null in docker-compose to keep the container running.

docker-compose.yml example

version: '3'
services:
  some-app:
    command: tail -f /dev/null

Why this command?

The only reason for choosing this option was that it received a lot of thumbs up on GitHub, but the highest voted answer does not mean that it is the best answer. The second reason was a pragmatic one as issues had to be solved as soon as possible due to deadlines.

Answer 4

• Create a file called docker-compose.yml
• Add the following to the file

version: "3"

services:
  ubuntu:
    image: ubuntu:latest
    tty: true

• Staying in the same directory, run docker-compose up -d from the terminal
• Run docker ps to get the container id or name
• You can run docker inspect $container_id
• You can enter the container and get a bash shell running docker-compose exec ubuntu /bin/bash or docker-compose exec ubuntu /bin/sh
• When done, make sure you are outside the container and run docker-compose down

Here's a small bash script (my-docker-shell.sh) to create the docker compose file, run the container, login to the container and then finally cleanup the docker container and the docker compose file when you log out.

#!/bin/bash

cat << 'EOF' > ./docker-compose.yml
---

version: "3"

services:
  ubuntu:
    image: ubuntu:latest
    command: /bin/bash
    # tty: true

...
EOF

printf "Now entering the container...\n"
docker-compose run ubuntu bash
docker-compose down

rm -v ./docker-compose.yml

Answer 5

In the Dockerfile you can use the command:

{CMD sleep infinity}

Answer 6

As the commenter stated, we'd have to see the Dockerfile in question to give you a complete answer, but this is a very common mistake. I can pretty much guarantee that the command you're trying to run is starting a background process. This might be the command you'd run in non-Docker situations, but it's the wrong thing to do in a Dockerfile. For instance, if what you're running is typically defined as a system service, you might use something like "systemctl start". That would start the process in the background, which will not work. You have to run the process in the foreground, so the entire process will block.

Answer 7

Just a quick note

I have tested single image based on golang, so when I call docker-compose down here what I get:

version: "3.1"
...
command: tail -f /dev/null   # stopping container takes about 10 sec.
tty: true                    # stopping container takes about 2 sec.

My system info:

Ubuntu 18.04.4 LTS (64-bit)
Docker version 19.03.6, build 369ce74a3c
docker-compose version 1.26.0, build d4451659

Answer 8

Some people here write about overwriting the entrypoint so that the command can also have its effect. But no one gives an example. I then:

docker-compose.yml:

version: '3'

services:

    etfwebapp:
        # For messed up volumes and `sudo docker cp`:
        command: "-f /dev/null"
        entrypoint: /usr/bin/tail
        tty: true

# ...

I am not sure if tty is needed at this point. Is it better to do it twice? In my case it did no harm and worked perfectly. Without entrypoint it didn't work for me because then command had no effect. So I guess for this solution tty is optional.

To understand which command is executed at start-up, simply read the entrypoint before the command (concat with space): /usr/bin/tail -f /dev/null.

Answer 9

Okay I found my mistake. In the Dockerfile for the image used for compose I specified that the base image should be ubuntu:latest, but I previously created an image called ubuntu by myself and that image did not work. So I did not use the original ubuntu image but rather a corrupt version of my own image also called ubuntu.