Is there a way to put a lock on Concourse git-resource? - concourse

Question

I have setup pipeline in Concourse with some jobs that are building Docker images.
After the build I push the image tag to the git repo.
The problem is when the builds come to end at the same time, one jobs pushes to git, while the other just pulled, and when second job tries push to git it gets error.
error: failed to push some refs to 'git#github.com:*****/*****'
hint: Updates were rejected because the remote contains work that you do
hint: not have locally. This is usually caused by another repository pushing
hint: to the same ref. You may want to first integrate the remote changes
hint: (e.g., 'git pull ...') before pushing again.
hint: See the 'Note about fast-forwards' in 'git push --help' for details.
So is there any way to prevent concurrent push?
So far I've tried applying serial and serial_groups to jobs.
It helps, but all the jobs got queued up, because we have a lot of builds.
I expect jobs to run concurrently and pause before doing operations to git if some other job have a lock on it.
resources:
- name: backend-helm-repo
type: git
source:
branch: master
paths:
- helm
uri: git#github.com:******/******
-...
jobs:
-...
- name: some-hidden-api-build
serial: true
serial_groups:
- build-alone
plan:
- get: some-hidden-api-repo
trigger: true
- get: golang
- task: build-image
file: somefile.yaml
- put: some-hidden-api-image
- get: backend-helm-repo
- task: update-helm-tag
config:
platform: linux
image_resource:
type: registry-image
source:
repository: mikefarah/yq
tag: latest
run:
path: /bin/sh
args:
- -xce
- "file manipulations && git commit"
inputs:
- name: some-hidden-api-repo
- name: backend-helm-repo
outputs:
- name: backend-helm-tag-bump
- put: backend-helm-repo
params:
repository: backend-helm-tag-bump
- put: some-hidden-api-status
params:
commit: some-hidden-api-repo
state: success
- name: some-other-build
serial: true
serial_groups:
- build-alone
plan:
- get: some-other-repo
trigger: true
- get: golang
- task: build-image
file: somefile.yaml
- put: some-other-image
- get: backend-helm-repo
- task: update-helm-tag
config:
platform: linux
image_resource:
type: registry-image
source:
repository: mikefarah/yq
tag: latest
run:
path: /bin/sh
args:
- -xce
- "file manipulations && git commit"
inputs:
- name: some-other-repo
- name: backend-helm-repo
outputs:
- name: backend-helm-tag-bump
- put: backend-helm-repo
params:
repository: backend-helm-tag-bump
- put: some-other-status
params:
commit: some-other-repo
state: success
-...
So if jobs come finish image build at the same time and make git commit in parallel, one pushes faster, than second one, second one breaks.
Can someone help?

Answer 1

note that your description is too vague to give detailed answer.
I expect jobs to concurrently and stop before pushing to git if some other job have a lock on git.
This will not be enough, if they stop just before pushing, they are already referencing a git commit, which will become stale when the lock is released by the other job :-)
The jobs would have to stop, waiting on the lock, before cloning the git repo, so at the very beginning.
All this is speculation on my part, since again it is not clear what you want to do, for these kind of questions posting a as-small-as-possible pipeline image and as-small-as-possible configuration code is helpful.
You can consider https://github.com/concourse/pool-resource as locking mechanism.