add parameter to specify docker tags

Author: jameslnewell

README.md

@@ -291,6 +291,24 @@ steps:
       - my-custom-plugin#v1.0.0:
 ```
 
+### Specifying tags to apply to the pushed Docker image
+
+By default, the image is tagged with the `latest` tag in addition to the cache key.
+
+By specifying the `tags` parameter you can specify your own set of tags to apply to the image:
+
+```yaml
+steps:
+  - command: echo wow
+    plugins:
+      - seek-oss/docker-ecr-cache#v2.0.0:
+          tags:
+            - latest
+            - build-${BUILDKITE_BUILD_NUMBER}
+```
+
+Specifying your own tags makes it easy to reuse the image later in the pipeline.
+
 ### AWS ECR specific configuration
 
 #### Specifying an ECR repository name

hooks/pre-command

@@ -71,13 +71,24 @@ if ! docker pull "${image}:${tag}"; then
   docker "${image_build_args[@]}" ${BUILDKITE_PLUGIN_DOCKER_ECR_CACHE_ADDITIONAL_BUILD_ARGS:-} "${context}" ||
     log_fatal "^^^ +++" 1
 
-  docker tag "${image}:${tag}" "${image}:latest"
-
-  echo "--- Pushing tag ${tag}"
+  echo "--- Pushing tags"
+  echo " - ${tag}"
   docker push "${image}:${tag}"
 
-  echo "--- Pushing tag latest"
-  docker push "${image}:latest"
+  results=()
+  read_list_property 'TAGS'
+  if [ "${#result[*]}" == "0" ]; then
+    echo " - latest"
+    docker tag "${image}:${tag}" "${image}:latest"
+    docker push "${image}:latest"
+  else
+    for other_tag in ${result[@]+"${result[@]}"}; do
+      echo " - ${other_tag}"
+      docker tag "${image}:${tag}" "${image}:${other_tag}"
+      docker push "${image}:${other_tag}"
+    done
+  fi
+
 fi || echo "Not found"
 
 # Support using https://github.com/buildkite-plugins/docker-buildkite-plugin without an image by default

plugin.yml

@@ -33,4 +33,6 @@ configuration:
       type: string
     region:
       type: string
+    tags:
+      type: [array, string]
   required: []