Compose CLI (v2) ignores some ports specified in docker-compose file when an override file is used.

[pratiksanglikar]

Description
When using docker-compose.yml file along with docker-compose.override.yml file, docker-compose CLI only maps the first port specified in the docker-compose.yml file.

Steps to reproduce the issue:

1. Create a sample docker-compose project using the getting started tutorial. Else clone pratiksanglikar/compose-sample and jump to step 5.
2. Modify the docker-compose.yml file to replace port entry "5000:5000" by "5000" to allocate host port dynamically.
3. Modify the docker-compose.yml file to add another port entry "6000".
   The final docker-compose.yml file looks like -

version: "3.9"
services:
  web:
    build: .
    ports:
      - "5000"
      - "6000"
  redis:
    image: "redis:alpine"

4. Add a docker-compose.override.yml file with the following contents -

version: "3.9"
services:
  web:
    container_name: python_webapp

5. Start the app using docker-compose up command.
6. Inspect the container created for the python app using docker inspect <container_id> command.
7. Look at the Ports section.

Describe the results you received:

"NetworkSettings": {
            "Ports": {
                "5000/tcp": null,
                "6000/tcp": [
                    {
                        "HostIp": "0.0.0.0",
                        "HostPort": "51220"
                    }
                ]
            },

Describe the results you expected:

"NetworkSettings": {
            "Ports": {
                "5000/tcp":  [
                    {
                        "HostIp": "0.0.0.0",
                        "HostPort": "51219"
                    }
                ],
                "6000/tcp": [
                    {
                        "HostIp": "0.0.0.0",
                        "HostPort": "51220"
                    }
                ]
            },

Additional information you deem important (e.g. issue happens only occasionally):

• The issue happens only if you specify ports to be allocated dynamically.
• The issue happens only if you have the docker-compose.override.yml file.

Output of docker-compose --version:

PS> docker-compose --version
Docker Compose version v2.0.0-rc.1

Output of docker version:

PS> docker version
Client:
 Cloud integration: 1.0.17
 Version:           20.10.8
 API version:       1.41
 Go version:        go1.16.6
 Git commit:        3967b7d
 Built:             Fri Jul 30 19:58:50 2021
 OS/Arch:           windows/amd64
 Context:           default
 Experimental:      true

Server: Docker Engine - Community
 Engine:
  Version:          20.10.8
  API version:      1.41 (minimum version 1.12)
  Go version:       go1.16.6
  Git commit:       75249d8
  Built:            Fri Jul 30 19:52:10 2021
  OS/Arch:          linux/amd64
  Experimental:     false
 containerd:
  Version:          1.4.9
  GitCommit:        e25210fe30a0a703442421b0f60afac609f950a3
 runc:
  Version:          1.0.1
  GitCommit:        v1.0.1-0-g4144b63
 docker-init:
  Version:          0.19.0
  GitCommit:        de40ad0

Output of docker context show:

PS> docker context show
default

Output of docker info:

PS> docker info
Client:
 Context:    default
 Debug Mode: false
 Plugins:
  buildx: Build with BuildKit (Docker Inc., v0.6.1-docker)
  compose: Docker Compose (Docker Inc., v2.0.0-rc.1)
  scan: Docker Scan (Docker Inc., v0.8.0)

Server:
 Containers: 35
  Running: 34
  Paused: 0
  Stopped: 1
 Images: 9
 Server Version: 20.10.8
 Storage Driver: overlay2
  Backing Filesystem: extfs
  Supports d_type: true
  Native Overlay Diff: true
  userxattr: false
 Logging Driver: json-file
 Cgroup Driver: cgroupfs
 Cgroup Version: 1
 Plugins:
  Volume: local
  Network: bridge host ipvlan macvlan null overlay
  Log: awslogs fluentd gcplogs gelf journald json-file local logentries splunk syslog
 Swarm: inactive
 Runtimes: io.containerd.runc.v2 io.containerd.runtime.v1.linux runc
 Default Runtime: runc
 Init Binary: docker-init
 containerd version: e25210fe30a0a703442421b0f60afac609f950a3
 runc version: v1.0.1-0-g4144b63
 init version: de40ad0
 Security Options:
  seccomp
   Profile: default
 Kernel Version: 5.10.43.3-microsoft-standard-WSL2
 Operating System: Docker Desktop
 OSType: linux
 Architecture: x86_64
 CPUs: 12
 Total Memory: 15.56GiB
 Name: docker-desktop
 ID: 55EY:A7SS:SC32:BZYI:ZHI4:KHXV:5RVM:PKV5:IT6U:4HMN:X3NV:EIKE
 Docker Root Dir: /var/lib/docker
 Debug Mode: false
 Registry: https://index.docker.io/v1/
 Labels:
 Experimental: false
 Insecure Registries:
  127.0.0.0/8
 Live Restore Enabled: false

WARNING: No blkio throttle.read_bps_device support
WARNING: No blkio throttle.write_bps_device support
WARNING: No blkio throttle.read_iops_device support
WARNING: No blkio throttle.write_iops_device support

Additional environment details (AWS ECS, Azure ACI, local, etc.):
Host machine: Windows
Containers: Linux