What does the wire format of an Avro Kafka record look like?

Magic byte + 4-byte schema ID + Avro-binary payload

Schema Registry Basics

Records carry a schema ID, not the schema itself. That's the whole trick.

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Schemas are part of your wire protocol

Why a registry

Without a contract, Kafka topics rot into garbage in months. The Schema Registry stores versioned schemas (Avro / Protobuf / JSON-Schema); records carry a 4-byte schema ID; consumers fetch the schema on demand and cache it.

Subjects are typically named <topic>-value and <topic>-key. Each subject has a compatibility level (BACKWARD, FORWARD, FULL, NONE) which gates new registrations.

Author an Avro schema for order.placed

Define an Avro record. Required fields: order_id (string), amount_cents (int), currency (string). Add an optional coupon_code so the first evolution exercise is easy.

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