部署到Go1.12的Google App Engine flexible失败

I have a service that looks somewhat like this -

service
  |
  |__cmd
  |  |_main.go
  |
  |_ app.yaml
  |_ cloudbuild.yaml
  |_ service.go
  |_ someHelper.go

I have a few private packages that I include in go.mod and after a lengthy build process I have an image that can be deployed to GAE. However, I get this error after I deploy -

Starting Step #6 - "deploy app"
Step #6 - "deploy app": Already have image (with digest): gcr.io/cloud-builders/gcloud
Step #6 - "deploy app": ERROR: (gcloud.app.deploy) Staging command [/builder/google-cloud-sdk/platform/google_appengine/go-app-stager /workspace/app.yaml /workspace /tmp/tmpuwereWq0/tmpdfWB0wiJ] failed with return code [1].
Step #6 - "deploy app":
Step #6 - "deploy app": ------------------------------------ STDOUT ------------------------------------
Step #6 - "deploy app": ------------------------------------ STDERR ------------------------------------
Step #6 - "deploy app": 2019/09/06 12:17:42 staging for go1.12
Step #6 - "deploy app": 2019/09/06 12:17:42 Staging Flex app: failed analyzing /workspace: the root of your app needs to be package "main" (currently "some_service_name")
Step #6 - "deploy app": GOPATH: /go
Step #6 - "deploy app": --------------------------------------------------------------------------------
Step #6 - "deploy app":
Finished Step #6 - "deploy app"

My cloud build sample file is posted here - https://gist.github.com/automaticalldramatic/961dbd2a92a6b9518835688eb2df2d67

Any help or insight would be appreciated :)