Troubleshooting Azure Event Hubs

This guide provides solutions to common issues you might encounter when working with Azure Event Hubs. We'll cover connectivity, message processing, performance, and more.

Connectivity Issues

Problem: Unable to connect to Event Hubs endpoint.

Possible Causes & Solutions:

  • Network Restrictions:
    • Ensure firewall rules (local or network) allow outbound traffic to Azure Event Hubs ports (e.g., 5671 for AMQP, 443 for HTTPS).
    • If using VNet Service Endpoints or Private Endpoints, verify network configuration and routing.
  • Authentication/Authorization Errors:
    • Verify connection strings are correct and contain the right Shared Access Signature (SAS) policy or Azure AD credentials.
    • Check if the SAS policy has the necessary 'Listen', 'Send', or 'Manage' permissions.
    • Ensure the identity used (SAS or Azure AD) has appropriate role assignments on the Event Hubs namespace.
  • DNS Resolution:
    • Confirm that the Event Hubs namespace hostname (e.g., `your-namespace.servicebus.windows.net`) can be resolved by your client.
  • Throttling:
    • Check for warnings or errors related to throttling in your logs. This might indicate you're exceeding ingress/egress quotas. Consider scaling up your Event Hubs tier or increasing the number of Throughput Units (TUs).
Problem: Connection drops frequently.

Possible Causes & Solutions:

  • Network Instability:
    • Monitor your network for packet loss or high latency.
    • Implement retry logic in your client applications with exponential backoff.
  • Idle Timeouts:
    • Ensure your client is sending heartbeats or keeping the connection alive if it's expected to be idle for extended periods. AMQP clients often handle this automatically.
  • Resource Exhaustion:
    • Check for resource constraints on the client machine (CPU, memory, network sockets).

Message Processing Issues

Problem: Messages are not appearing in the Event Hub.

Possible Causes & Solutions:

  • Producer Errors:
    • Review producer application logs for any exceptions during message sending.
    • Verify that the producer is successfully connecting and receiving acknowledgments (if applicable).
    • Ensure the correct Event Hub name and namespace are used in the connection string.
  • Incorrect Partition Key:
    • If using partition keys, ensure they are consistently applied for related messages. If no key is specified, messages are distributed round-robin.
  • Throttling (Producer):
    • If the producer is being throttled, messages might be temporarily rejected or delayed. Monitor Event Hubs metrics for ingress throttling.
Problem: Consumer is not receiving messages or is missing messages.

Possible Causes & Solutions:

  • Consumer Group Configuration:
    • Ensure the consumer is using the correct consumer group name. If a consumer group doesn't exist, it will be created.
    • Verify that the consumer is not infinitely looping on the same set of messages due to incorrect offset management.
  • Offset Management:
    • Consumers are responsible for tracking their own offset. If an application restarts, it needs to know where to resume. Azure SDKs often manage this with checkpointing (e.g., to Azure Blob Storage). Ensure checkpointing is configured correctly and functional.
  • Partition Ownership:
    • Event Hubs uses consumer groups and epoch-based ownership for load balancing. Ensure consumers within the same consumer group don't interfere with each other's processing by checking for "Partition owner lost" or similar errors.
  • Filter Issues:
    • If using message filters or the Event Hubs SDK's `EventPosition`, ensure the starting point is correct. A common mistake is setting `EventPosition.Latest` which will miss historical messages. Use `EventPosition.FromEnqueuedTime()` or `EventPosition.FromSequenceNumber()` to specify a starting point.
  • Consumer Throttling:
    • While less common for receiving, if your consumer is processing messages very slowly, it might indirectly affect availability. Check egress metrics.
Problem: Messages are received out of order.

Possible Causes & Solutions:

  • Partitioning:
    • Event Hubs guarantees ordering within a partition. If messages arrive at Event Hubs with different partition keys, they might be directed to different partitions and processed independently, potentially leading to out-of-order reception across partitions.
    • If strict ordering is required across all messages, use a single partition or a partition key that consistently directs related messages to the same partition.
  • Consumer Logic:
    • Your consumer application might be reordering messages unintentionally. Ensure your processing logic preserves order if necessary.

Performance and Throttling

Problem: Experiencing high latency or low throughput.

Possible Causes & Solutions:

  • Throughput Unit (TU) Limits:
    • Event Hubs performance is tied to the number of TUs configured for the namespace. Check the "Ingress/Egress Throughput" and "Throttled Requests" metrics in Azure Monitor.
    • If you are hitting TU limits, increase the number of TUs or scale to a higher tier (e.g., Standard to Premium).
  • Partition Limits:
    • Each partition has its own ingress and egress limits. If you have many partitions but few are active, you might be limited by the per-partition limits. Conversely, if you have few partitions and high load, you might hit aggregate TU limits.
    • Consider increasing the number of partitions if your workload can be parallelized effectively.
  • Batching and Compression:
    • For producers, batching messages before sending can significantly improve throughput and reduce costs.
    • Consider using compression if your messages are large and repetitive. Azure SDKs often support this.
  • Client-Side Bottlenecks:
    • Ensure your producer and consumer applications are not the bottleneck. Monitor their CPU, memory, and network utilization.
    • Optimize serialization/deserialization processes.
  • Network Latency:
    • High latency between your application and Azure Event Hubs can impact performance. Deploy your applications in the same Azure region as your Event Hubs namespace.
Throttling is a Signal: Throttled requests indicate that you are exceeding the allocated TUs or partition limits. This is a key metric to monitor for performance tuning.

General Troubleshooting Tips