use GCR mirror for pulling images
diff --git a/tools/internal_ci/helper_scripts/prepare_build_linux_rc b/tools/internal_ci/helper_scripts/prepare_build_linux_rc
index ea2a17f..8715d6c 100644
--- a/tools/internal_ci/helper_scripts/prepare_build_linux_rc
+++ b/tools/internal_ci/helper_scripts/prepare_build_linux_rc
@@ -22,6 +22,9 @@
# Move docker's storage location to scratch disk so we don't run out of space.
echo 'DOCKER_OPTS="${DOCKER_OPTS} --graph=/tmpfs/docker"' | sudo tee --append /etc/default/docker
+# Use container registry mirror for pulling docker images (should make downloads faster)
+# See https://cloud.google.com/container-registry/docs/using-dockerhub-mirroring
+echo 'DOCKER_OPTS="${DOCKER_OPTS} --registry-mirror=https://mirror.gcr.io"' | sudo tee --append /etc/default/docker
sudo service docker restart
# Populate xdg-cache-home to workaround https://github.com/grpc/grpc/issues/11968