Another option to handle a "cold start" of the ServiceBusTrigger function is using an eventing feature of the Azure Event Grid, where the events are emitted immediately if there are no messages in the Service Bus entity and a new message arrives. See more details here.
Note, that the event is emitted immediately when the first message arrived into the service bus entity. In the case, when the messages are there, the next event is emitted based on the idle time of the listener/receiver. This idle (watchdog) time is periodically 120 seconds from the last time used the listener/receiver on the service bus entity.
This is a push model, no listener on the service bus entity, so the AEG Subscriber (EventGridTrigger function) will "balanced" receiving a message with the ServiceBusTrigger function (its listener/receiver).
Using the REST API for deleting/receiving a message from the service bus entity (queue), the subscriber can obtained it very easy and straightforward.
So, using the AEG eventing on the topic providers/Microsoft.ServiceBus/namespaces/myNamespace and filtering on the eventType = "Microsoft.ServiceBus.ActiveMessagesAvailableWithNoListeners", the messages can be received side by side with a ServiceBudTrigger function and to solve the AF problem on the "cold start".
Note, that only the Azure Service Bus premium tier is integrated to AEG.
The following code snippet shows an example of the AEG Subscriber for Service Bus using the EventGridTrigger function:
#r "Newtonsoft.Json"
using System;
using System.Threading.Tasks;
using System.Text;
using System.Linq;
using System.Net;
using System.Net.Http;
using System.Web;
using Newtonsoft.Json;
using Newtonsoft.Json.Linq;
public static async Task Run(JObject eventGridEvent, ILogger log)
{
log.LogInformation(eventGridEvent.ToString());
string requestUri = $"{eventGridEvent["data"]?["requestUri"]?.Value<string>()}";
if(!string.IsNullOrEmpty(requestUri))
{
using (var client = new HttpClient())
{
client.DefaultRequestHeaders.Add("Authorization", Environment.GetEnvironmentVariable("AzureServiceBus_token"));
var response = await client.DeleteAsync(requestUri);
// status & headers
log.LogInformation(response.ToString());
// message body
log.LogInformation(await response.Content.ReadAsStringAsync());
}
}
await Task.CompletedTask;
}
