Not able to trigger jobs one after the other using gcs-resource in concourse - concourse

Question

I have two jobs viz. build and publish. I want publish to trigger after build is done. So, I am using an external resource gcs-resourcehttps://github.com/frodenas/gcs-resource
Following is my pipeline.yml:
---
resource_types:
- name: gcs-resource
type: docker-image
source:
repository: frodenas/gcs-resource
resources:
- name: proj-repo
type: git
source:
uri: <my uri>
branch: develop
username: <username>
password: <password>
- name: proj-gcr
type: docker-image
source:
repository: asia.gcr.io/myproject/proj
tag: develop
username: _json_key
password: <my password>
- name: proj-build-output
type: gcs-resource
source:
bucket: proj-build-deploy
json_key: <my key>
regexp: Dockerfile
jobs:
- name: build
serial_groups: [proj-build-deploy]
plan:
- get: proj
resource: proj-repo
- task: build
config:
platform: linux
image_resource:
type: docker-image
source: {repository: node, tag: 10.13.0}
inputs:
- name: proj
run:
path: sh
args:
- -exc
- |
<do something>
- put: proj-build-output
params:
file: proj/Dockerfile
content_type: application/octet-stream
- name: publish
serial_groups: [proj-build-deploy]
plan:
- get: proj-build-output
trigger: true
passed: [build]
- put: proj-gcr
params:
build: proj-build-output
I am using the external resource proj-build-output to trigger the next job. I can run the individual jobs without any problem, however the the publish job doesn't automatically get triggered after completion of build job.
Am I missing something?

Answer 1

The regexp of the gcs-resource is misconfigured:
...
regexp: Dockerfile
...
while regexp, as the original S3 resource from which it comes from, wants:
regexp: the pattern to match filenames against within GCS. The first grouped match is used to extract the version, or if a group is explicitly named version, that group is used.
The https://github.com/frodenas/gcs-resource#example-configuration shows its correct usage:
regexp: directory_on_gcs/release-(.*).tgz
This is not specific to the GCS or S3 resource; Concourse needs a "version" to move artifacts from jobs to storage and back. It is one of the fundamental concepts of Concourse. See https://web.archive.org/web/20171205105324/http://concourse.ci:80/versioned-s3-artifacts.html for an example.

Answer 2

As Marco mentioned, the problem was with versioning.
I solved my issue using these two steps:
Enabled versioning on my GCS Bucket https://cloud.google.com/storage/docs/object-versioning#_Enabling
Replaces regexp with versioned_file as mentioned in the docs https://github.com/frodenas/gcs-resource#file-names