Is it possible to run commands inside of a running Docker container?

[helmut72]

Some of my apps need to run regular cronjobs inside of a running container. After reading the docs, it looks like Dagu can only run commands in new containers, but not run a command inside of a running container? Or do I miss something?

Thank you.

[yohamta]

@helmut72
Hi thanks for the question. I am not sure if I understand correctly, so if not please let me know.
If you need to run a command inside an already running container, you can use docker exec as a DAG step command if the container is running on the local docker host, but I guess it's not the answer you want.

Would you mind more clarification and context on what you are trying to do?

[helmut72]

Hi, thanks for your answer.

Sorry I forgot to mention that I let run Dagu as a Container. You are right, docker exec is possible, but docker-cli package isn't included in Dagus image. This makes me wonder why Dagu can run a new docker image, but I don't see any possibility how to run a command in a container. Then I've asked ;)

In the meantime I have built my own Dagu image with docker-cli included.

But could it be that Dagu handles quotes something special?

I want run following command from Dagu:

command: docker exec freshrss /bin/bash -c 'for i in $(/usr/bin/php /var/www/html/cli/list-users.php);do /usr/bin/php /var/www/html/cli/db-optimize.php --user $i;done'

I have tried over an hour combinations with backslashes, single and double quotes, but nothing works. One combination run the for loop because I see the ouput of db-optimize twice, but it doesn't use the variable.

The same command runs as expected from shell, when connected into Dagu container.

Thank you.

Edit:
Puttying the command into a common shell script and running it with command: /path/to/myscript.sh works. Maybe I should go this way.

[yohamta]

@helmut72
Hi thanks for providing the details.
I am afraid that writing a script inside a DAG would be easier for a complex command.

For example:

steps:
  - name: run docker container
    command: bash
    script: |
      docker exec freshrss /bin/bash -c 'for i in $(/usr/bin/php /var/www/html/cli/list-users.php);do /usr/bin/php /var/www/html/cli/db-optimize.php --user $i;done'

This way you can write any bash script inside the field script in the DAG, could you please give it a try?
Thanks!

[helmut72]

HI, thanks for your answer.

This works!

But I go the way to run scripts from the command. Reason is that other scripts requires error checks and I want to have scripts stored always in the same location, near the app.

A dag file should be only "register" a cronjob when an app goes up and will be deleted, when the app goes down. For example backup jobs. Webinterface of Dagu should be just a little overview about current tasks.

Btw, great peace of software!