[BUG] `docker compose ps --format json` no longer returns an array in 2.21.0

[unikitty37]

Description

The release notes for 2.21.0 state "Changed docker compose ps and docker compose ps --format=json output to align with Docker CLI."

However, in prior versions, the result was a valid JSON array. 2.21.0 returns individual objects, one after the other, with no [ … ] wrapper. This doesn't seem to be valid JSON.

Although jq can handle this, Ruby's JSON.parse rejects it as invalid; I've not tried other parsers.

Was this intended?

Steps To Reproduce

1. With any Compose project, run docker compose up -d.
2. Run docker-compose ps --format json.

Versions before 2.21.0 will return an array of objects; version 2.21.0 will return sequential objects, separated only by a new line.

Compose Version

% docker compose version
Docker Compose version v2.21.0
% docker-compose version
Docker Compose version v2.21.0

Docker Environment

Client:
 Version: 24.0.5
 Context: orbstack
 Debug Mode: false
 Plugins:
 buildx: Docker Buildx (Docker Inc.)
 Version: v0.11.1
 Path: /Users/username/.docker/cli-plugins/docker-buildx
 compose: Docker Compose (Docker Inc.)
 Version: v2.21.0
 Path: /Users/username/.docker/cli-plugins/docker-compose
 dev: Docker Dev Environments (Docker Inc.)
 Version: v0.1.0
 Path: /Users/username/.docker/cli-plugins/docker-dev
 extension: Manages Docker extensions (Docker Inc.)
 Version: v0.2.20
 Path: /Users/username/.docker/cli-plugins/docker-extension
 init: Creates Docker-related starter files for your project (Docker Inc.)
 Version: v0.1.0-beta.6
 Path: /Users/username/.docker/cli-plugins/docker-init
 sbom: View the packaged-based Software Bill Of Materials (SBOM) for an image (Anchore Inc.)
 Version: 0.6.0
 Path: /Users/username/.docker/cli-plugins/docker-sbom
 scan: Docker Scan (Docker Inc.)
 Version: v0.26.0
 Path: /Users/username/.docker/cli-plugins/docker-scan
 scout: Command line tool for Docker Scout (Docker Inc.)
 Version: 0.20.0
 Path: /Users/username/.docker/cli-plugins/docker-scout

Server:
 Containers: 22
 Running: 11
 Paused: 0
 Stopped: 11
 Images: 23
 Server Version: 24.0.5
 Storage Driver: overlay2
 Backing Filesystem: btrfs
 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 logentries splunk syslog
 Swarm: inactive
 Runtimes: io.containerd.runc.v2 runc
 Default Runtime: runc
 Init Binary: docker-init
 containerd version: fe457eb99ac0e27b3ce638175ef8e68a7d2bc373
 runc version: 82f18fe0e44a59034f3e1f45e475fa5636e539aa
 init version: de40ad0
 Security Options:
 seccomp
 Profile: builtin
 cgroupns
 Kernel Version: 6.4.13-orbstack-00090-ga4cfdc88d4df
 Operating System: OrbStack
 OSType: linux
 Architecture: aarch64
 CPUs: 10
 Total Memory: 11.67GiB
 Name: orbstack
 ID: 437f17f3-56ac-4f55-ad12-6154b025c473
 Docker Root Dir: /var/lib/docker
 Debug Mode: false
 Experimental: true
 Insecure Registries:
 127.0.0.0/8
 Registry Mirrors:
 http://192.168.69.99:13588/
 Live Restore Enabled: false
 Product License: Community Engine
 Default Address Pools:
 Base: 192.168.215.0/24, Size: 24
 Base: 192.168.228.0/24, Size: 24
 Base: 192.168.247.0/24, Size: 24
 Base: 192.168.207.0/24, Size: 24
 Base: 192.168.167.0/24, Size: 24
 Base: 192.168.107.0/24, Size: 24
 Base: 192.168.237.0/24, Size: 24
 Base: 192.168.148.0/24, Size: 24
 Base: 192.168.214.0/24, Size: 24
 Base: 192.168.165.0/24, Size: 24
 Base: 192.168.227.0/24, Size: 24
 Base: 192.168.181.0/24, Size: 24
 Base: 192.168.158.0/24, Size: 24
 Base: 192.168.117.0/24, Size: 24
 Base: 192.168.155.0/24, Size: 24
 Base: 192.168.147.0/24, Size: 24
 Base: 192.168.229.0/24, Size: 24
 Base: 192.168.183.0/24, Size: 24
 Base: 192.168.156.0/24, Size: 24
 Base: 192.168.97.0/24, Size: 24
 Base: 192.168.171.0/24, Size: 24
 Base: 192.168.186.0/24, Size: 24
 Base: 192.168.216.0/24, Size: 24
 Base: 192.168.242.0/24, Size: 24
 Base: 192.168.166.0/24, Size: 24
 Base: 192.168.239.0/24, Size: 24
 Base: 192.168.223.0/24, Size: 24
 Base: 192.168.164.0/24, Size: 24
 Base: 192.168.163.0/24, Size: 24
 Base: 192.168.172.0/24, Size: 24
 Base: 172.17.0.0/16, Size: 16
 Base: 172.18.0.0/16, Size: 16
 Base: 172.19.0.0/16, Size: 16
 Base: 172.20.0.0/14, Size: 16
 Base: 172.24.0.0/14, Size: 16
 Base: 172.28.0.0/14, Size: 16

Anything else?

json_files.zip

This is occurring with OrbStack; Docker Desktop is still providing Docker Compose version v2.20.2-desktop.1, and is thus unaffected for now.

[glours]

Hey @unikitty37
This is expected and mentioned in the v2.21.0 release notes. We aligned the docker compose ps format to the docker ps one, for more details see #10918

[unikitty37]

Got it — thanks! I was reading the release notes at https://docs.docker.com/compose/release-notes/, which don't have links to the underlying tickets. Would it be worth explicitly mentioning this there?

[glours]

Sure I'll open a PR to mention it there 👍

[unikitty37]

Thanks!

[philBrown]

Doesn't this represent a breaking change, requiring a major version bump?

[tingstad]

Doesn't this represent a breaking change, requiring a major version bump?

It certainly broke several of our builds since GitHub recently updated its Ubuntu runner images to use 2.21.0.

[veaviticus]

The docker compose docs (https://docs.docker.com/engine/reference/commandline/compose_ps/#format) also still claim the output is array-formatted JSON, instead of a jsonlines-esque format.