Docker Compose build fails with failed to parse platform: "" is an invalid OS component on Windows Server 2019 + Kali Linux

[MrMiningIR]

Hi everyone,

I installed Windows Server 2019, Kali Linux, and Docker.

When I try to run the project with:
docker-compose up

I get the following error:

bash

Sending build context to Docker daemon  7.082MB
Step 1/41 : FROM --platform=$BUILDPLATFORM oven/bun:1 AS frontend-builder
[+] up 0/1
 - Image ghcr.io/hkuds/lightrag:latest Building 1.3s
failed to parse platform : "" is an invalid OS component of "": OSAndVersion specifier component must match "^([A-Za-z0-9_-]+)(?:\\(([A-Za-z0-9_.%-]*)((?:\\+[A-Za-z0-9_.%-]+)*)\\))?$": invalid argument

It seems the problem is related to this line in the Dockerfile:

FROM --platform=$BUILDPLATFORM oven/bun:1 AS frontend-builder

From what I understand, $BUILDPLATFORM is empty or not being detected correctly in my environment.

My environment
Windows Server 2019
Kali Linux
Docker installed
Running the project with docker-compose up

My question
How can I fix this issue?

Do I need to:

set BUILDPLATFORM manually,
use Docker Buildx,
update Docker / Docker Compose,
or remove --platform=$BUILDPLATFORM from the Dockerfile?
Any help would be appreciated.

Thanks.

[daveshenal]

Hii MrMiningIR,

$BUILDPLATFORM is a special variable that Docker only fills in automatically when BuildKit is doing the build. If the build falls back to the old "classic" builder, that variable stays empty - and --platform="" is invalid, which is exactly this error.

This almost always happens with the legacy Python docker compose (v1) binary which matches the error format you are seeing (ERROR: Service 'X' failed to build). On Kali, apt install docker-compose still often pulls in this old v1 package instead of the modern Compose plugin, and v1 doesn't reliably wire up BuildKit.

Fix:

1. Switch to Compose V2 (the docker compose command, with a space - not the hyphenated docker-compose):

sudo apt remove docker-compose
sudo apt install docker-compose-plugin

2. Make sure BuildKit is enabled:

export DOCKER_BUILDKIT=1
export COMPOSE_DOCKER_CLI_BUILD=1

(add these to ~/.bashrc to persist)

3. Retry with:

  docker compose up --build

If it still fails, check docker version. Anything below 20.10 should be updated, since BuildKit support needs a reasonably recent Docker Engine.

You don't need to edit the Dockerfile or remove --platform=$BUILDPLATFORM as that line is correct and standard for multi stage cross platform builds. The fix belongs on the tooling side (Compose V2 + BuildKit), not the Dockerfile itself.