Cancel job within CircleCI workflow when another workflow with that job is triggered - circleci

Question

Let's say we have a workflow called Workflow1 which contains jobs A, B, C and D.
First developer pushes a change and triggers Workflow1.
Second developer also pushes a change and triggers Workflow1.
Is there a way to ensure that when job C starts in the second developer's workflow, it automatically cancels only job C in the first developer's workflow, without affecting any of the other jobs?

Answer 1

You could implement something using the CircleCI API v2 and some jq wizardry. Note: you'll need to create a personal API token, and store it in an environment variable (let's call it MyToken)
I'm suggesting the below approach, but there could be another (maybe simpler ¯\_(ツ)_/¯) way.
Get the IDs of pipelines in the project that have the created status:
PIPE_IDS=$(curl --header "Circle-Token: $MyToken" --request GET "https://circleci.com/api/v2/project/gh/$CIRCLE_PROJECT_USERNAME/$CIRCLE_PROJECT_REPONAME/pipeline?branch=$CIRCLE_BRANCH"|jq -r '.items[]|select(.state == "created")')
Get the IDs of currently running/on_hold workflows with the name Workflow1 excluding the current workflow ID:
if [ ! -z "$PIPE_IDS" ]; then
for PIPE_ID in $PIPE_IDS
do curl --header "Circle-Token: $MyToken" --request GET "https://circleci.com/api/v2/pipeline/${PIPE_ID}/workflow"|jq -r --arg CIRCLE_WORKFLOW_ID "$CIRCLE_WORKFLOW_ID" '.items[]|select(.status == "on_hold" or .status == "running")|select(.name == "Workflow1")|select(.id != $CIRCLE_WORKFLOW_ID)|.id' >> currently_running_Workflow1s.txt
done
fi
Then (sorry, I'm getting a bit lazy here, and you also need to do some of the work :p), use the currently_running_Workflow1s.txt file generated above and the "Get a workflow's jobs" endpoint to get the job number of each job in the related running Workflow1 workflows whose name matches job C and that has a status running.
Finally, use the "Cancel job" endpoint to cancel each of these jobs.
Note that there might be a slight delay between the "cancel API call" and the job actually being cancelled, so you might want to add
a short sleep, or even better a while loop that checks those
jobs' respective statuses, before moving further.
I hope this helps.