From 2c062b0a9c5c6ab9bbdb1e01688c2f7b760f87ef Mon Sep 17 00:00:00 2001
From: Quentin Gliech <quenting@element.io>
Date: Mon, 27 Jul 2026 13:52:50 +0200
Subject: [PATCH] Use the Docker build cache in the ESS test suite

Import the Docker build cache that the Build workflow pushes to ghcr.io on
main, which caches the toolchain, frontend and policy layers
---
 .github/workflows/ci.yaml | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/.github/workflows/ci.yaml b/.github/workflows/ci.yaml
index 81619c040..610da7ff5 100644
--- a/.github/workflows/ci.yaml
+++ b/.github/workflows/ci.yaml
@@ -380,10 +380,19 @@ jobs:
         with:
           ess-helm-ref: ${{ steps.check-branch.outputs.ref }}
 
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@d7f5e7f509e45cec5c76c4d5afdd7de93d0b3df5 # v4.1.0
+        with:
+          buildkitd-config-inline: |
+            [registry."docker.io"]
+              mirrors = ["mirror.gcr.io"]
+
       - name: Build MAS docker image to local registry
-        run: |
-          docker build -t localhost:5000/matrix-authentication-service:ci -f ./Dockerfile .
-          docker push localhost:5000/matrix-authentication-service:ci
+        uses: docker/build-push-action@53b7df96c91f9c12dcc8a07bcb9ccacbed38856a # v7.3.0
+        with:
+          cache-from: type=registry,ref=ghcr.io/element-hq/matrix-authentication-service/buildcache:buildcache-amd64
+          push: true
+          tags: localhost:5000/matrix-authentication-service:ci
 
       - name: Build Additional values file
         run: >