CREATED BY CHAINLINK LABS A minimal example that, on a cron schedule, reads a value from an AWS S3 object, increments it, and writes it backāusing CRE (Chainlink Runtime Environment) with SigV4-signed HTTP requests.
The workflow:
- Retrieves
AWS_ACCESS_KEY_IDandAWS_SECRET_ACCESS_KEYfrom CRE Secrets - Signs the request with AWS SigV4 (timestamp sourced from the consensus runtime)
- Reads the S3 object (initializes to
0if missing) - Aggregates the current value across nodes (median), increments once, and writes the agreed next value back
Setup & Run
1 Provide AWS credentials as secrets
Add the following secrets to your CRE environment:
AWS_ACCESS_KEY_ID
AWS_SECRET_ACCESS_KEY
(For local testing, ensure these are available to the simulator via your environment variables.)
2 Configure the workflow
Create/update my-workflow/config.json with your S3 details:
{
"schedule": "* * */1 * * *",
"aws_region": "my-aws-region",
"s3_bucket": "product-release-bucket",
"s3_key": "cre-counter.txt"
}
scheduleuses a 6-field cron expression with seconds (e.g.,* * */1 * * *runs every hour).aws_regionis the AWS region of your bucket.s3_bucketis the bucket name.s3_keyis the object path that stores the counter.
3 Run a local simulation
From your project root:
cre workflow simulate my-workflow
You should see output similar to:
Workflow compiled
2025-11-03T16:31:45Z [SIMULATION] Simulator Initialized
2025-11-03T16:31:45Z [SIMULATION] Running trigger [email protected]
2025-11-03T16:31:45Z [USER LOG] msg="Cron trigger fired. Fetching AWS credentials..."
2025-11-03T16:31:45Z [USER LOG] msg="AWS credentials fetched. Performing consensus read, then write."
2025-11-03T16:31:45Z [USER LOG] msg="Consensus old value computed. Incrementing." old=2 new=3
2025-11-03T16:31:45Z [USER LOG] msg="Workflow finished successfully." old=2 new=3
Workflow Simulation Result:
{
"NewValue": "3",
"OldValue": "2"
}
2025-11-03T16:31:45Z [SIMULATION] Execution finished signal received
2025-11-03T16:31:45Z [SIMULATION] Skipping WorkflowEngineV2