chore: bake sccache into dynamo base (#6532)

.github/workflows/build-frontend-image.yaml

@@ -142,9 +142,10 @@ jobs:
         id: calculate-target-tag
         shell: bash
         run: |
+          ECR_IMAGE_BASE="${{ env.ECR_HOSTNAME }}/${{ env.IMAGE_REGISTRY }}/${{ env.IMAGE_REPOSITORY }}"
           TARGET_TAG="${{ github.sha }}-${{ env.TARGET }}-${{ matrix.arch }}"
-          DEFAULT_TARGET_IMAGE_URI="${{ env.ECR_HOSTNAME }}/${{ env.IMAGE_REGISTRY }}/${{ env.IMAGE_REPOSITORY }}:${TARGET_TAG}"
-          echo "default_target_image_uri=${DEFAULT_TARGET_IMAGE_URI}" >> $GITHUB_OUTPUT
+          echo "ecr_image_base=${ECR_IMAGE_BASE}" >> $GITHUB_OUTPUT
+          echo "default_target_image_uri=${ECR_IMAGE_BASE}:${TARGET_TAG}" >> $GITHUB_OUTPUT
           echo "epp_image_uri=${{ env.ECR_HOSTNAME }}/${{ needs.build-epp-image.outputs.epp_image_ref }}" >> $GITHUB_OUTPUT
           echo "target_tag=${TARGET_TAG}" >> $GITHUB_OUTPUT
           echo "azure_target_image_uri=${{ secrets.AZURE_ACR_HOSTNAME }}/${{ env.IMAGE_REGISTRY }}/${{ env.IMAGE_REPOSITORY }}:${TARGET_TAG}" >> $GITHUB_OUTPUT
@@ -192,9 +193,9 @@ jobs:
           extra_build_args: |
             EPP_IMAGE=${{ steps.calculate-target-tag.outputs.epp_image_uri }}
           extra_tags: |
-            ${{ steps.calculate-target-tag.outputs.azure_target_image_uri }}
-            ${{ github.ref_name == 'main' && format('main-frontend-{0}', matrix.arch) || '' }}
-            ${{ github.ref_name == 'main' && format('main-frontend-{0}-{1}', github.sha, matrix.arch) || '' }}
+            ${{ matrix.arch == 'amd64' && steps.calculate-target-tag.outputs.azure_target_image_uri || '' }}
+            ${{ github.ref_name == 'main' && format('{0}:main-frontend-{1}', steps.calculate-target-tag.outputs.ecr_image_base, matrix.arch) || '' }}
+            ${{ github.ref_name == 'main' && format('{0}:main-frontend-{1}-{2}', steps.calculate-target-tag.outputs.ecr_image_base, github.sha, matrix.arch) || '' }}
 
       - name: Show summary
         shell: bash

container/templates/dynamo_base.Dockerfile

@@ -15,6 +15,15 @@ ARG ARCH_ALT
 USER root
 WORKDIR /opt/dynamo
 
+# Install sccache into the base image so downstream stages can COPY it
+# instead of downloading from GitHub (avoids 502 errors under parallel builds)
+ARG SCCACHE_VERSION=v0.14.0
+RUN wget --tries=3 --waitretry=5 \
+        "https://github.com/mozilla/sccache/releases/download/${SCCACHE_VERSION}/sccache-${SCCACHE_VERSION}-${ARCH_ALT}-unknown-linux-musl.tar.gz" && \
+    tar -xzf "sccache-${SCCACHE_VERSION}-${ARCH_ALT}-unknown-linux-musl.tar.gz" && \
+    mv "sccache-${SCCACHE_VERSION}-${ARCH_ALT}-unknown-linux-musl/sccache" /usr/local/bin/ && \
+    rm -rf sccache*
+
 # Install uv package manager
 COPY --from=ghcr.io/astral-sh/uv:latest /uv /uvx /bin/
 

container/templates/wheel_builder.Dockerfile

@@ -130,7 +130,11 @@ RUN git clone --depth 1 --branch ${NIXL_GDRCOPY_REF} https://github.com/NVIDIA/g
     rpm -Uvh gdrcopy-*.el8.${ARCH_ALT}.rpm && \
     rpm -Uvh gdrcopy-devel-*.el8.noarch.rpm
 
-# Install SCCACHE if requested
+# sccache binary is pre-installed in dynamo_base;
+# COPY it so the install call below skips the GitHub download.
+# Wrapper scripts (sccache-cc, sccache-cxx) are created by use-sccache.sh install.
+COPY --from=dynamo_base /usr/local/bin/sccache /usr/local/bin/sccache
+
 ARG USE_SCCACHE
 ARG SCCACHE_BUCKET
 ARG SCCACHE_REGION

container/use-sccache.sh

@@ -44,18 +44,20 @@ EOF
 }
 
 install_sccache() {
+    if command -v sccache >/dev/null 2>&1; then
+        echo "sccache already installed at $(command -v sccache), skipping download"
+    else
         if [ -z "${ARCH_ALT:-}" ]; then
             echo "Error: ARCH_ALT environment variable is required for sccache installation"
             exit 1
         fi
         echo "Installing sccache ${SCCACHE_VERSION} for architecture ${ARCH_ALT}..."
-    # Download and install sccache
         wget --tries=3 --waitretry=5 \
             "https://github.com/mozilla/sccache/releases/download/${SCCACHE_VERSION}/sccache-${SCCACHE_VERSION}-${ARCH_ALT}-unknown-linux-musl.tar.gz"
         tar -xzf "sccache-${SCCACHE_VERSION}-${ARCH_ALT}-unknown-linux-musl.tar.gz"
         mv "sccache-${SCCACHE_VERSION}-${ARCH_ALT}-unknown-linux-musl/sccache" /usr/local/bin/
-    # Cleanup
         rm -rf sccache*
+    fi
 
     # Create compiler wrapper scripts for autotools/Meson compatibility.
     # Autoconf breaks with CC="sccache gcc" (multi-word value), so we provide