Single gitlab cache with pull-only behavior

.gitlab-ci.yml

@@ -21,13 +21,15 @@ variables:
   image: datadog/dd-trace-java-docker-build:latest
   before_script:
     - export GRADLE_USER_HOME=`pwd`/.gradle
-  cache:
-    key: '$CI_COMMIT_REF_SLUG' # Cache per branch
-    paths:
-      - .gradle/wrapper
-      - .gradle/caches
 
-build:
+cache:
+  key: '$CI_SERVER_VERSION' # Reset the cache every time gitlab is upgraded.  ~Every couple months
+  paths:
+    - .gradle/wrapper
+    - .gradle/caches
+  policy: pull
+
+build: &build
   <<: *gradle_build
   stage: build
   script:
@@ -38,9 +40,21 @@ build:
       - 'workspace/dd-java-agent/build/libs/*.jar'
       - 'upstream.env'
 
+build_with_cache:
+  <<: *build
+  rules:
+    - if: '$POPULATE_CACHE'
+      when: on_success
+    - when: manual
+  cache:
+    policy: push
+
 deploy_to_reliability_env:
   stage: deploy
-  when: on_success
+  rules:
+    - if: '$POPULATE_CACHE'
+      when: never
+    - when: on_success
   trigger:
     project: DataDog/datadog-reliability-env
     branch: $DOWNSTREAM_BRANCH