𝗕𝘂𝗶𝗹𝗱𝗶𝗻𝗴 𝗔𝗻 𝗘𝘃𝗲𝗻𝘁 𝗕𝘂𝘀 𝗪𝗶𝘁𝗵 𝗘𝘅𝗮𝗰𝘁𝗹𝘆 𝗢𝗻𝗰𝗲 𝗗𝗲𝗹𝗶𝘃𝗲𝗿𝘆

𝗕𝘂𝗶𝗹𝗱𝗶𝗻𝗴 𝗔𝗻 𝗘𝘃𝗲𝗻𝘁 𝗕𝘂𝘀 𝗪𝗶𝘁𝗵 𝗘𝘅𝗮𝗰𝘁𝗹𝘆-𝗢𝗻𝗰𝗲 𝗗𝗲𝗹𝗶𝘃𝗲𝗿𝘆

Sending events between microservices is hard. You want events to arrive exactly once. Not zero times. Not twice.

Here is a blueprint for a robust event bus.

The Tech Stack:

• PostgreSQL for durable storage.
• Redis for fast queuing.
• Python for the logic.

The Strategy:

• Use a durable event log.
• Track delivery attempts.
• Use idempotency keys.

How the flow works:

• A publisher sends an event.
• The bus saves it with a unique ID in PostgreSQL.
• A worker puts the event in a Redis queue.
• The consumer receives the event.
• The consumer checks an idempotency table.
• If the ID exists, the consumer skips the work.
• If the ID is new, the consumer processes the event and saves the ID.

Key Tables:

• Events: stores payloads and IDs.
• Delivery Attempts: tracks status and retries.
• Consumer Idempotency: tracks processed events per consumer.

Operational Tips:

• Use a dead-letter queue for permanent failures.
• Apply exponential backoff for retries.
• Monitor success rates with a dashboard.

Source: https://dev.to/therizwansaleem/building-a-robust-server-side-event-bus-with-exactly-once-delivery-in-a-microservice-architecture-3fa4