Image build is optimized.

.gitlab-ci.yml

@@ -50,7 +50,9 @@ build:
   image: docker:20.10.16
   services:
     - name: docker:20.10.16-dind
-      command: ["--host=tcp://0.0.0.0:2375", "--tls=false", "--storage-driver=overlay2", "--mtu=1500", "--data-root=/mnt/volume"]
+      command: ["--host=tcp://docker:2375", "--tls=false", "--storage-driver=overlay2", "--mtu=1500", "--data-root=/mnt/volume"]
+      volumes:
+        - /var/run/docker.sock:/var/run/docker.sock
   script:
     - docker info
     - docker buildx create --use