Apex Async & Integration

Decision tree

• Small deferred unit of work -> Queueable.
• Very large data set -> Batch Apex or an external bulk-processing mechanism.
• Time-based execution -> Schedulable, usually delegating to Queueable/Batch.
• Legacy/simple async requirement -> @future only when its constraints fit; do not introduce it by default.
• Event-driven decoupling -> Platform Events / Change Data Capture when appropriate.
• External HTTP callout -> Named Credential / External Credential plus an async boundary if the invocation context cannot perform a callout.

Queueable

• Pass only serializable, bounded state.
• Avoid chaining indefinitely.
• Design idempotency when retries or duplicate execution are possible.
• Make failure handling observable.

Batch