Fix #858: tell buildx which platform to build for

.github/workflows/ci_docker_tests.yaml

@@ -66,7 +66,13 @@ jobs:
           submodules: recursive
 
       - name: Build Docker images
-        run: docker compose build
+        run: |
+          # Running locally, a plain "docker compose build" works as expected.
+          # On GitHub, buildx tries to build all 3 images in parallel even if
+          # you set COMPOSE_PARALLEL_LIMIT or use --parallel 1. That fails b/c
+          # the qsim-base image is not available to the other two build jobs.
+          docker compose build qsim-base-image
+          docker compose build qsim-cxx-tests-image qsim-py-tests-image
 
       - name: Run C++ tests
         run: docker run --rm qsim-cxx-tests:latest
@@ -75,7 +81,7 @@ jobs:
         run: docker run --rm qsim-py-tests:latest
 
       - name: Run a sample simulation
-        run: docker run --rm qsim:latest -c /qsim/circuits/circuit_q24
+        run: docker run --rm qsim-base:latest -c /qsim/circuits/circuit_q24
 
       - name: Test installation process
         run: |

Dockerfile

@@ -1,5 +1,5 @@
 # Base OS
-FROM ubuntu:24.04
+FROM ubuntu:24.04 AS qsim-base
 
 # Allow passing this variable in from the outside.
 ARG CUDA_PATH

docker-compose.yml

@@ -1,23 +1,26 @@
 services:
-    qsim:
-        image: qsim
-        container_name: qsim
+    qsim-base-image:
+        image: qsim-base
+        platform: linux/amd64
         build:
             context: ./
             dockerfile: Dockerfile
-    qsim-cxx-tests:
+            target: qsim-base
+
+    qsim-cxx-tests-image:
         image: qsim-cxx-tests
-        container_name: qsim-cxx-tests
         build:
             context: ./
             dockerfile: tests/Dockerfile
+            target: qsim-cxx-tests
         depends_on:
-        - qsim
-    qsim-py-tests:
+          - qsim-base-image
+
+    qsim-py-tests-image:
         image: qsim-py-tests
-        container_name: qsim-py-tests
         build:
             context: ./
             dockerfile: pybind_interface/Dockerfile
+            target: qsim-py-tests
         depends_on:
-        - qsim
+          - qsim-base-image

pybind_interface/Dockerfile

@@ -1,5 +1,5 @@
 # Base OS
-FROM qsim
+FROM qsim-base AS qsim-py-tests
 
 # Copy relevant files
 COPY ./pybind_interface/ /qsim/pybind_interface/

tests/Dockerfile

@@ -1,5 +1,5 @@
 # Base OS
-FROM qsim
+FROM qsim-base AS qsim-cxx-tests
 
 # Copy relevant files
 COPY ./tests/ /qsim/tests/