ryacron

ryacron is a Rust-based cron runner inspired by yacron.

The current MVP focuses on a practical local use case: acting as a lightweight EventBridge emulator that invokes Cargo Lambda functions on a cron schedule.

Status

This project is intentionally small for now.

• YAML-driven job definitions
• Global timezone per config file
• 6-field cron expressions via tokio-cron-scheduler
• Cargo Lambda execution backend
• Payload from file or generated EventBridge-like event
• Per-job timeout
• Per-job max concurrent runs with skip-on-limit behavior

The long-term direction is to keep the project name and config model generic while allowing more execution backends in the future.

Installation

cargo build

Usage

Run the scheduler with a YAML config file:

cargo run -- run --config ./ryacron.yaml

If you already built the binary:

./target/debug/ryacron run --config ./ryacron.yaml

The process keeps running until you stop it with Ctrl-C.

Configuration

Example:

timezone: Asia/Tokyo

jobs:
  - name: batch_job_a
    schedule: "0 * * * * *"
    function: batch_job_q
    payload:
      file: examples/eventbridge.json
    timeout_seconds: 600
    max_concurrent_runs: 1

  - name: batch_job_b
    schedule: "0 */5 * * * *"
    function: batch_job_b
    payload:
      generate_eventbridge_scheduled_event: true
    timeout_seconds: 600
    max_concurrent_runs: 5

Top-level fields

• timezone: IANA timezone name such as Asia/Tokyo or UTC
• jobs: list of scheduled jobs

Job fields

• name: human-readable job name
• schedule: cron expression in sec min hour dom mon dow format
• function: Cargo Lambda function name passed to cargo lambda invoke
• payload: optional payload source
• timeout_seconds: optional timeout in seconds
• max_concurrent_runs: optional positive integer, defaults to 1

Payload modes

payload may specify exactly one of the following:

payload:
  file: path/to/event.json

or

payload:
  generate_eventbridge_scheduled_event: true

If payload is omitted, ryacron invokes the function without --data-file.

Concurrency control

max_concurrent_runs controls how many invocations of the same job may run at once.

• If omitted, the default is 1
• If the job is already running max_concurrent_runs times, the next scheduled invoke is skipped
• 1 matches the old "no overlap" behavior

Example:

jobs:
  - name: batch_job
    schedule: "0 * * * * *"
    function: batch-job
    max_concurrent_runs: 5

In this example, up to 5 concurrent cargo lambda invoke processes may run for batch_job. If 5 are already running, the next tick is skipped.

Cron format

ryacron currently requires exactly 6 cron fields:

sec min hour day-of-month month day-of-week

Examples:

• "0 * * * * *": every minute
• "0 */5 * * * *": every 5 minutes
• "30 0 9 * * 1-5": 09:00:30 on weekdays

5-field cron expressions are rejected in the current MVP.

EventBridge-like generated payload

When generate_eventbridge_scheduled_event: true is used, ryacron generates a minimal event payload with these fields:

• id
• time
• source
• detail-type
• resources
• detail

This is meant for local development and testing, not strict AWS EventBridge parity.

Validation rules

At startup, ryacron validates:

• YAML syntax
• timezone value
• cron format
• payload shape
• payload file existence
• max_concurrent_runs >= 1

Invalid configuration causes startup to fail with a non-zero exit code.

Logging behavior

The scheduler writes simple human-readable logs to standard output and standard error, including:

• scheduler start and stop
• job start
• job success or failure
• timeout
• overlap skip

Current limitations

• only one executor backend: Cargo Lambda CLI
• no hot reload
• no separate validate command yet
• no per-job timezone
• no persistent execution history
• no strict yacron compatibility guarantee

Development

Format and test locally:

cargo fmt
cargo test

Show CLI help:

cargo run -- --help

License

This project is licensed under the terms of the LICENSE file.