Immutable-Service-Bus

• Azure Function App project that demonstrates how to use a lock to prevent processing the same message more than once. Which may be possible when an app scale out to multiple instances:

  • The Service Bus function trigger has an "at least once" message delivery policy:

    • Azure Functions Service Bus trigger bindings
    • Azure Service Bus Messaging - Receive Modes
    • Azure Functions Idempotent Execution

  • High-level workflow: HTTP trigger function -> Service Bus queue -> Service Bus queue trigger function -> Lock file in Blob Storage

    • HTTP trigger function: Triggered by an HTTP request from a client. The HTTP request should contain the message content. The function then sends a message to the Service Bus queue.
    • Service Bus queue trigger function: Triggered by a Service Bus queue message.
      • Checks if there is an active lock for the message ID of the message using a blob storage client.
        • If there is an active lock, the current function execution fails due to an exception with the following message: "The message ID dbce9dc2685c4997acb05f2067ed29a3 has an active lock lock-dbce9dc2685c4997acb05f2067ed29a3.lock until 2024-02-19 00:24:41.314111"
        • (Acquire lock) If there is an expired lock, then the lock is updated which sets a new expiration time and a new owner (the current function) by updating the blob file's metadata.
        • (Acquire lock) If there is no lock, then a blob file/lock is created for the current function execution.
      • Releases lock by deleting the blob file.

• TODO: consider lock expiration for current function execution. how should this be handled.

  • after every complete opperation a check point could be created or appended (maybe to the lock blob file)
  • use Azure functions function execution timeout property to end any execution that has a duration >= 5mins