# Azure Function

有 2 個模式，以未來性來說，Isolated 比較好，因為可以支援後續的 .Net 7, .Net 8，只需要升級 .Net Version 就好了。

* Isolated Process (Out of Process)
* In Process

[In-Process vs. Isolated Process](https://docs.microsoft.com/en-us/azure/azure-functions/dotnet-isolated-process-guide#differences-with-net-class-library-functions)


Ref: https://markheath.net/post/azure-functions-isolated

**本機開發前須要先安裝以下工具：**
1. [Azure Functions Core Tools](https://docs.microsoft.com/zh-tw/azure/azure-functions/functions-run-local?tabs=v4%2Cwindows%2Ccsharp%2Cportal%2Cbash)
2. [.Net Runtime](https://dotnet.microsoft.com/en-us/download/dotnet/6.0), version up than 6.0.6

**Command Line：**

func init {project_name} #建立一個可以用 Visual Studio Code 開啟的 Azure Function專案
func new #建立一個Function Class

**Duration Function:**
Ref: https://docs.microsoft.com/zh-tw/azure/azure-functions/durable/durable-functions-overview?tabs=csharp

**Trigger Type：**
Ref: https://docs.microsoft.com/en-us/azure/azure-functions/functions-triggers-bindings?tabs=csharp#supported-bindings

**Request Body Example:**
Ref: https://stackoverflow.com/questions/66911660/httprequestdata-wraps-body-in-json

**HttpTrigger Authorization Level:**
Ref: https://vincentlauzon.com/2017/12/04/azure-functions-http-authorization-levels/

**Cold Start**
Ref. https://azure.microsoft.com/zh-tw/blog/understanding-serverless-cold-start/

**Azure Function Timeout:**

**functionTimeout：** 整個 Function Timeout 的時間
**maxAutoLockRenewalDuration：** Function 過多久之內沒有結束的話，ServiceBus 會重打一次 Azure Function 的時間

Ref: https://build5nines.com/azure-functions-extend-execution-timeout-past-5-minutes/
Ref. https://docs.microsoft.com/en-us/azure/azure-functions/functions-host-json#functiontimeout
Ref. https://docs.microsoft.com/en-us/azure/azure-functions/functions-bindings-service-bus?tabs=in-process%2Cextensionv5%2Cextensionv3&pivots=programming-language-csharp#hostjson-settings

**HealthCheck Monitor**
Ref: https://github.com/Azure/azure-functions-host/wiki/Host-Health-Monitor

**Output Binding:**

Function Return 時在 Response Model 的 Property 加上對應的 Output Attribute，就會自動轉發到對應的 ServiceBus 上了

[Function("ServiceBusProducerBindOutput")]
public async Task<Output> Run([HttpTrigger(AuthorizationLevel.Anonymous, "get", "post")] HttpRequestData req,
    FunctionContext executionContext)
{
    var queueBody = new QueueBody
    {
        ProcessId = Guid.NewGuid(),
        Content = "ConsumerWithBind"
    };

    await _stepRepository.AddStep(queueBody.ProcessId, 0, queueBody.Content, "Queue");

    var response = req.CreateResponse(HttpStatusCode.OK);
    await response.WriteAsJsonAsync<object>(new {result = true});

    return new Output
    {
        Body = queueBody,
        result = response
    };
}

public class Output
{
    [ServiceBusOutput(queueOrTopicName: "mainqueue", Connection = "ServiceBus")]
    public QueueBody Body { get; set; }

    public HttpResponseData result { get; set; }
}

ServiceBusTrigger 可以只接用 Class 來接收 Input，不需特別用 String 接下來再轉成 Json

[Function("ServiceBusConsumer")]
public async Task Run([ServiceBusTrigger("mainqueue", Connection = "ServiceBus")] QueueBody body, FunctionContext context)
{
    await _stepRepository.AddStep(body.ProcessId, 1, body.Content, "Queue");
}

### ServiceBusTrigger
ServiceBus 有 2 種類型，Queue 跟 Topic：

**Queue:**
* Queue 是一對一的，不會同時發送給多個 Consumer

:::info
Queue 只能有一個 Consumer，如果刻意綁定多個的話，只會有一個 Consumer 收到 Message

:::

**Topic:**
* 一個 Topic 裡面可以設定好幾個 Subscriptions，每個 Subscription 都會有一個 Consumer，只要發送一個 Message 到這個 Topic，Topic 中的所有 Subscriptions 都會收到同樣的訊息。
* Topic 可以透過在 Subscription 設定 EnabledSession 來保證 Message 是以 FIFO 的方式消耗的，但需要在程式中指定一個 SessionId 來讓 Subscription 辨認他們是同一批的，如果沒有設定 SessionId 的話，設定為 EnabledSession 的 Subsciption 不會將訊息轉發給 Consumer


:::info
2 個 Subscription 同時都收到 Message

:::

###### tags: `Azure`