Troubleshooting Azure Event Hubs

This guide provides common issues and their resolutions when working with Azure Event Hubs.

Common Issues and Solutions

1. Connection Errors

Symptom: Applications fail to connect to Event Hubs with errors like "Unauthorized" or "The remote host closed the connection unexpectedly."

• Check Firewall Rules: Ensure that your network firewall allows outbound connections to Event Hubs endpoints on ports 443 (HTTPS) and 5671 (AMQP).
• Verify Connection String/Credentials: Double-check your Event Hubs connection string or Shared Access Signature (SAS) keys for correctness. Ensure they have the necessary permissions (e.g., Send, Listen).
• Namespace Status: Verify that your Event Hubs namespace is healthy and running in the Azure portal.
• IP Filtering: If you have IP filtering enabled on your Event Hubs namespace, ensure that the IP address of your client application is allowed.
• SDK Version: Ensure you are using a recent and supported version of the Azure SDK for your programming language.

2. Message Sending Failures

Symptom: Messages are not appearing in Event Hubs, or sending operations return errors such as "Request too large" or "Quota exceeded."

• Message Size Limits: Event Hubs has a maximum message size limit (currently 256 KB for standard tier). Ensure your individual messages do not exceed this limit. Consider batching or compressing larger messages if necessary.
• Throughput Limits: You might be exceeding the configured throughput units (TUs) or processing units (PUs) for your Event Hubs namespace. Monitor metrics like "Ingress throughput" and "Ingress messages" in the Azure portal. Scale up your TUs/PUs if needed.
• Event Hub Capacity: Ensure the specific Event Hub within the namespace has sufficient capacity.
• Batching Logic: If you are batching messages, verify your batching logic. Ensure you are not creating overly large batches that exceed the limits or leaving messages un-sent due to incorrect batch closing.

3. Message Receiving Issues

Symptom: Applications are not receiving messages, or are receiving duplicate messages, or messages are being dropped.

• Consumer Group Configuration: Ensure your consumer group is correctly configured and that there isn't another consumer in the same consumer group reading the same partition without proper coordination.
• Checkpointing: If using libraries like Event Hubs for Apache Kafka (EH Kafka) or Azure SDK with checkpointing, ensure that your checkpointing mechanism is functioning correctly. Stale checkpoints can cause consumers to miss messages.
• Last Enqueued Sequence Number: Compare the last enqueued sequence number with the last processed sequence number to identify potential message gaps.
• Message Expiration: Event Hubs messages are retained for a configured duration (e.g., 1 day by default, up to 7 days). If your consumer is too slow, messages might expire before they are read.
• Partition Deadlocks: In high-throughput scenarios, ensure your receivers are properly handling partition ownership and not getting into a state where a partition is not being actively read.

4. Latency Problems

Symptom: High latency between message publishing and consumption.

• Network Latency: Check the network latency between your publisher and Event Hubs, and between Event Hubs and your consumer. Deploying resources in the same Azure region can significantly reduce latency.
• Throughput Limits: If you're hitting throughput limits, it can cause messages to be queued up, increasing latency.
• Processing Logic: The processing logic within your consumer can be a bottleneck. Optimize your message processing code.
• SDK Configuration: Some SDKs have configurable buffer sizes or prefetch settings that can affect latency.

5. Quota and Throttling

Symptom: Operations are being throttled with "ServerBusy" errors.

• Exceeding Throughput Limits: This is the most common cause. As mentioned earlier, monitor TUs/PUs and scale accordingly.
• Request Rate Limits: Azure Event Hubs also has limits on the number of requests per second. Distribute your requests over time if possible.
• Retries and Backoff: Implement a robust retry strategy with exponential backoff in your client applications to handle transient throttling.

6. Issues with Event Hubs for Apache Kafka

Symptom: Kafka clients are unable to connect or produce/consume messages.

• Authentication: Ensure you are using the correct connection string and authentication mechanism provided for EH Kafka.
• Bootstrap Servers: Verify that your Kafka clients are configured with the correct Event Hubs bootstrap server addresses.
• SASL Mechanism: Ensure your Kafka clients are configured to use the correct SASL mechanism (e.g., SASL.PLAIN or SASL.SCRAM-SHA-512) and that the username/password correspond to your SAS token.
• API Version Compatibility: Check for compatibility issues between your Kafka client version and the Event Hubs Kafka endpoint.

General Troubleshooting Steps

1. Check Azure Status: Visit the Azure status page to check for any ongoing service incidents in your region.
2. Monitor Metrics: Utilize the Azure portal's metrics for Event Hubs (e.g., connection count, ingress/egress throughput, request rate, throttling errors).
3. Review Logs: Enable and examine diagnostic logs and application logs for detailed error messages.
4. Simplify Your Scenario: Try to reproduce the issue with a minimal client application to isolate the problem.
5. Consult Documentation: Refer to the official Azure Event Hubs documentation for the latest information and best practices.
6. Seek Support: If you are unable to resolve the issue, consider reaching out to Azure support.