When architecting a solution in Azure, it is always important to keep in mind any limitations which might apply. These limitations can come not only from tier choice but also from technical restrictions. Here, we will have a look at the Service Bus throttling conditions, and how to handle them. When you are at the documentation page, it is clear there are several thresholds which will affect the maximum throughput achieved before running into throttling conditions.

  • Queue/topic size
  • Number of concurrent connections on a namespace
  • Number of concurrent receive requests on a queue/topic/subscription entity
  • Message size for a queue/topic/subscription entity
  • Number of messages per transaction

Azure Service Bus Throttling conditions

Each of these conditions has their characteristics and ways in which to handle them when they occur. It is important to understand each, as it allows us to take decisions on the following steps. And, set up a resilient architecture to minimize risks. Let us have a look at each and at the options to mitigate these thresholds.

Queue/topic size

This threshold stands for the maximum size of a Service Bus entity and defined when creating the queue or topic. When messages are not retrieved from the entity or retrieved slower than they are sent in. The entity will fill until it reaches this size. Once the entity hits this limit, it will reject new incoming messages and throws a QuotaExceededException exception back to the sender. Maximum entity size can be 1, 2, 3, 4 or 5 GB for the basic or standard tier without partitioning. 80GB standard tier with partitioning enabled as well as for the premium tier.

When this occurs, one option is to add more message receivers, to ensure our entity can keep up with the ingested messages. If the entity is not under our control, another option would be to catch the exception, and use an exponential backoff retry mechanism. By implementing an exponential backoff, receivers get a chance to catch up with processing the messages in the queue. Another option is to have the receivers use prefetching, which allows higher throughput, clearing the messages in our entity at a faster rate.

Number of concurrent connections on a namespace

The second threshold discussed in this post is about the number of connections allowed to be open simultaneously to a Service Bus namespace. Once all of these are in use, our entity will reject subsequent connection requests, throwing a QuotaExceededException exception. To mitigate this condition it is essential to know that queues share their connections between senders and receivers. Topics, on the other hand, have a separate pool of connections for the senders and receivers. The protocol used for communication is also essential, as NetMessaging allows for 1000 connections, while AMQP gives us 5000 connections.

This means that as the owner of the entities, there is the possibility to switch from queues to topics, effectively doubling the number of connections. Beware though, this will only increase the number of total allowed connections, but if there is already a large number of senders or receivers, it will still just give us the maximum of connections the chosen protocol gives us for each of these. If the sender or receiver client is under our control, there is also the option to switch protocols, which could provide us with five times the amount of connections when switching from NetMessaging to AMQP.

Monitoring

When working with Service Bus, it is crucial to implement a suitable monitoring strategy. There are several options to do this, ranging from the built-in tooling in Azure to using a third-party product like Serverless360. Each of these solutions has their strengths and weaknesses. When it comes to watching the Service Bus throttling state, Azure Monitor has recently added new metrics which allow us to do just that. These capabilities are currently in preview and gives several metrics to keep an eye on Service Bus namespaces and entities. One of these metrics is Throttled Requests, giving us insights into the number of requests throttled.

Throttling monitoring

Subsequently, it is even possible to set up alerts on top of these metrics, which you can accomplish through Azure Monitor. Add an alert rule for this scenario. These rules define when to trigger alerts, and which actions to take.

Serverless360 provides easy configuration and notification options for Azure service bus monitoring and raise alerts for Service Bus Throttling conditions.

Conclusion

When setting up an architecture with Azure services it is always important to keep an eye on the capabilities. In this case, we investigate Service Bus throttling conditions. Often, mitigation is done by adjusting some of the properties of our clients or implementing a retry strategy. Additionally, to keep clear insights into our environment, a monitoring strategy needs to be implemented for our situation. Where alerts are triggered in case any of these throttling conditions occur.

Originally published at Serverles360 site