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1. Schema of the incoming Avro records is expected to be the same for all messages between two flushes of the SystemProducer. This is because an Avro file expects all of its entries to conform to a schema and here blob is an Avro file.
2. OutgoingMessageEnvelope.key will be ignored here. This is because the Avro blobs created consist of only the schema taken from the OutgoingMessageEnvelope.message.getSchema and all the messages which are Avro records. There is no way to insert a key into the records as that would make the record incompatible with the schema. Other implementations of AzureBlobWriter can utilize the key in a meaning fashion.
3. Optionally, OutgoingMessageEnvelope.message can be a byte array provided the first message to the SystemProducer or the first message sent after a flush is an Avro record. The first message being an Avro record is needed to get the schema for the Avro file. If the subsequent messages are byte arrays, then the byte arrays are appended to the Avro file (aka blob) directly without any check to see if the byte array indeed is an encoded Avro record which adheres to the schema of the Avro file. It is responsibility of the user of the SystemProducer to ensure that the byte arrays are valid failing which the resulting Azure file (aka blob) will be unreadable.

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