Cache Docker builder stages in Drone CI for faster builds

Push intermediate builder stages as :builder tags and use cache_from
to reuse dependency layers (pip install, npm ci) across builds.

.drone.yml

@@ -14,6 +14,21 @@ trigger:
     - push
 
 steps:
+  - name: Cache builder stage
+    image: plugins/docker
+    settings:
+      username: viktorbarzin
+      password:
+        from_secret: dockerhub-token
+      repo: viktorbarzin/immoweb
+      dockerfile: frontend/Dockerfile
+      context: frontend
+      target: builder
+      cache_from:
+        - viktorbarzin/immoweb:builder
+      tags:
+        - builder
+
   - name: Build frontend image
     image: plugins/docker
     settings:
@@ -23,6 +38,9 @@ steps:
       repo: viktorbarzin/immoweb
       dockerfile: frontend/Dockerfile
       context: frontend
+      cache_from:
+        - viktorbarzin/immoweb:builder
+        - viktorbarzin/immoweb:latest
       tags:
         - latest
         - ${DRONE_BUILD_NUMBER}
@@ -78,6 +96,21 @@ trigger:
     - push
 
 steps:
+  - name: Cache builder stage
+    image: plugins/docker
+    settings:
+      username: viktorbarzin
+      password:
+        from_secret: dockerhub-token
+      repo: viktorbarzin/realestatecrawler
+      dockerfile: Dockerfile
+      context: .
+      target: builder
+      cache_from:
+        - viktorbarzin/realestatecrawler:builder
+      tags:
+        - builder
+
   - name: Build API image
     image: plugins/docker
     settings:
@@ -87,10 +120,12 @@ steps:
       repo: viktorbarzin/realestatecrawler
       dockerfile: Dockerfile
       context: .
+      cache_from:
+        - viktorbarzin/realestatecrawler:builder
+        - viktorbarzin/realestatecrawler:latest
       tags:
         - latest
         - ${DRONE_BUILD_NUMBER}
-      cache_from: viktorbarzin/realestatecrawler:latest
 
   - name: Update deployment
     image: alpine