[BUG] `--index` for `docker-compose exec` command does not choose right container

[gburzynski-10clouds]

Description

I have 2 containers created from the same service server. One with backend, second with tests. I want to exec into backend container.

e99c12cd8eeb   d1cc9cdbcd1b   "./run_tests.sh"   28 minutes ago   Up 28 minutes                                                     server-run-68082c734962
e24541534a85   d1cc9cdbcd1b   "python manage.py ru…"   29 minutes ago   Up 29 minutes   0.0.0.0:8001->8001/tcp, :::8001->8001/tcp         server

Doesn't matter if I run: docker-compose --file docker-compose.yml exec -t --index 0 server bash or docker-compose --file docker-compose.yml exec -t --index 1 server bash I end up inside test container (can be checked by looking into running processes ps aux.)

Workaround: docker-compose exec execs always into container that was created last.

Steps To Reproduce

1. Define server service in docker-compose.yml
2. Run one instance docker-compose --file docker-compose.yml run --rm --name server server python
3. Run second instance docker-compose --file docker-compose.yml run --rm server ./run_tests.sh
4. See the docker ps -a output to get the index of container
5. Notice that passed index does not change to which container we exec into docker-compose --file docker-compose.yml exec -t --index 1 server bash

Compose Version

2.29.7

Docker Environment

docker info Client: Docker Engine - Community Version: 27.3.1 Context: colima-redacted Debug Mode: false

Server: Containers: 4 Running: 4 Paused: 0 Stopped: 0 Images: 4 Server Version: 27.1.1 Storage Driver: overlay2 Backing Filesystem: extfs Supports d_type: true Using metacopy: false Native Overlay Diff: true userxattr: false Logging Driver: json-file Cgroup Driver: cgroupfs Cgroup Version: 2 Plugins: Volume: local Network: bridge host ipvlan macvlan null overlay Log: awslogs fluentd gcplogs gelf journald json-file local splunk syslog Swarm: inactive Runtimes: io.containerd.runc.v2 runc Default Runtime: runc Init Binary: docker-init containerd version: 472731909fa34bd7bc9c087e4c27943f9835f111 runc version: v1.1.13-0-g58aa920 init version: de40ad0 Security Options: apparmor seccomp Profile: builtin cgroupns Kernel Version: 6.8.0-41-generic Operating System: Ubuntu 24.04.1 LTS OSType: linux Architecture: aarch64 CPUs: 8 Total Memory: 9.69GiB Name: colima-redacted ID: af1bee08-e490-44cd-a00a-c182c012f6f4 Docker Root Dir: /var/lib/docker Debug Mode: false Experimental: false Insecure Registries: 127.0.0.0/8 Live Restore Enabled: false

Anything else?

No response

[ndeloof]

--index applies to containers created by up command. When you target containers created by run it has no effect, as such container as not indexed. Flag should be rejected to avoid confusion, so let's keep this tagged as a bug