Add BUILDKIT_INLINE_CACHE build arg to docker builder step (#3245)

# What this PR does
`BUILDKIT_INLINE_CACHE` is required by `--cache-from`, otherwise it
won't work.
It will improve build speeds when running `tilt up`

## Which issue(s) this PR fixes

## Checklist

- [ ] Unit, integration, and e2e (if applicable) tests updated
- [ ] Documentation added (or `pr:no public docs` PR label added if not
required)
- [ ] `CHANGELOG.md` updated (or `pr:no changelog` PR label added if not
required)

.drone.yml

@@ -107,6 +107,8 @@ steps:
       target: prod
       config:
         from_secret: gcr_admin
+      build_args:
+        - BUILDKIT_INLINE_CACHE=1
     depends_on:
       - Lint Backend
       - Unit Test Backend
@@ -128,6 +130,8 @@ steps:
         from_secret: docker_password
       username:
         from_secret: docker_username
+      build_args:
+        - BUILDKIT_INLINE_CACHE=1
     depends_on:
       - Lint Backend
       - Unit Test Backend
@@ -244,6 +248,11 @@ steps:
     # Be aware that the this plugin requires privileged capabilities, otherwise the integrated
     # Docker daemon is not able to start.
     privileged: true
+    environment:
+      # force docker to use buildkit feature, this will skip build stages that aren't required in
+      # the final image (ie. dev & dev-enterprise)
+      # https://github.com/docker/cli/issues/1134#issuecomment-406449342
+      DOCKER_BUILDKIT: 1
     settings:
       repo: grafana/oncall
       tags: latest,${DRONE_TAG}
@@ -255,6 +264,8 @@ steps:
         from_secret: docker_password
       username:
         from_secret: docker_username
+      build_args:
+        - BUILDKIT_INLINE_CACHE=1
     depends_on:
       - set engine version
 

Tiltfile

@@ -31,13 +31,11 @@ def plugin_json():
 
 allow_k8s_contexts(["kind-kind"])
 
-local_resource("download-cache", cmd="docker pull grafana/oncall:latest; docker tag grafana/oncall localhost:63628/grafana/oncall:latest")
-
 # Build the image including frontend folder for pytest
 docker_build_sub(
     "localhost:63628/oncall/engine:dev",
     context="./engine",
-    cache_from="localhost:63628/grafana/oncall:latest",
+    cache_from="grafana/oncall:latest",
     # only=["./engine", "./grafana-plugin"],
     ignore=["./grafana-plugin/test-results/", "./grafana-plugin/dist/", "./grafana-plugin/e2e-tests/"],
     child_context=".",