# Service Bus, Event Grid and Event Hubs — Azure

Source: https://www.skillbyai.com/en/azure/s-messaging

> Choose between commands, discrete events and event streams.

## Three messaging services, three jobs

**Azure Service Bus** is an enterprise message broker for **commands and business messages** that must not be lost: queues (one consumer gets each message) and topics with subscriptions (each subscription gets a copy). It offers peek-lock delivery, **dead-letter queues**, sessions for ordered processing and scheduled messages. **Azure Event Grid** routes **discrete events** ("a blob was created", "a resource group was deleted") from a source to handlers by **push**, with filtering and retries; it is how you react to things happening. **Azure Event Hubs** ingests **high-volume event streams** (telemetry, clickstreams, logs) into partitions that consumers read at their own pace and can replay; it also exposes a Kafka-compatible endpoint. Ask: is this an instruction someone must act on (Service Bus), a notification of a fact (Event Grid), or a firehose to analyse (Event Hubs)?

## Sending and receiving with Service Bus

Peek-lock: the message is completed only after successful processing, otherwise it returns to the queue and eventually dead-letters.

```python
from azure.identity import DefaultAzureCredential
from azure.servicebus import ServiceBusClient, ServiceBusMessage

NS = "sb-shop-dev.servicebus.windows.net"
with ServiceBusClient(NS, DefaultAzureCredential()) as client:
    with client.get_queue_sender("payments") as sender:
        sender.send_messages(ServiceBusMessage('{"orderId": 42}', message_id="order-42"))

    with client.get_queue_receiver("payments", max_wait_time=5) as receiver:
        for msg in receiver:
            try:
                handle(str(msg))
                receiver.complete_message(msg)
            except Exception:
                receiver.abandon_message(msg)
```

## Courier, notice board and CCTV recorder

Service Bus is a registered courier: a parcel for one recipient with a receipt. Event Grid is a notice board that pings everyone subscribed when a notice goes up. Event Hubs is a CCTV recorder: a continuous stream you can rewind and watch again.

**Quiz:** IoT devices send millions of telemetry readings per minute that several analytics jobs must read and replay. Which service fits?

- [ ] Service Bus queue
- [x] Event Hubs
- [ ] Event Grid
- [ ] Azure Files

*Answer:* Event Hubs. Event Hubs is built for partitioned, high-throughput streams that consumers can read independently and replay.