sjurkuhn/docker-swarm-exec repository overview

⁠docker-swarm-exec

A tool for executing commands in service containers deployed on Docker swarm - equivalent to:

docker service exec <task_id> <command> <args>

⁠Background

Docker Swarm does not yet provide a way to execute commands inside a service task from the manager node (CLI or API). This project provides an easy-to-use mechanism for doing just that: executing a command in the container of a service task.

Think of it as a docker service exec that applies to a specific task of a service.

The need for this project is expected to go away when the Support for executing into a task #1895⁠ issue is resolved in the Docker swarm project and the same capability becomes available directly in the Docker swarm API and command-line client.

⁠Standalone Use

On the swarm manager node, run the following command:

docker run -v /var/run/docker.sock:/var/run/docker.sock
    sjurkuhn/docker-swarm-exec \
    task-exec <taskID> <command> [<arguments>...]

where:

• <taskID> is the task ID of the task in which you want to execute a command (see task IDs with docker service ps <service_name>)
• <command> command to execute (e.g. curl)
• <arguments>... zero or more arguments to pass to the command (e.g., http://example.com/file)

⁠How It Works (Internals)

Starting from a task ID and a command to execute, here are the steps that are taken:

1. Obtain the node ID on which the target task is running, as well as the container ID of the task on that node
2. Create a temporary service, using the same container image, and a scheduling constraint that places the task of the temporary service on the same node where the target task is
3. Execute the equivalent of a docker exec command using the node-local Docker engine API
4. Upon completion of the command, terminate the temporary service, propagating the exit code of the executed command
5. Upon termination of the temporary service, extract the exit code and return it

⁠License

This is an open source project. See the LICENSE⁠ file.

⁠Contributing

If you want to propose an improvement, issues and pull requests are always welcome!