在Azure隔离函数中刷新AppConfiguration值时如何刷新服务

默认情况下，AddHttpClient注册时的配置委托只会执行一次，所以当App Config中的BaseUrl变更后，已创建的HttpClient不会自动更新BaseAddress。你可以通过以下两种方式实现动态刷新：

方法一：使用IOptionsMonitor在请求时动态更新BaseAddress #

通过IOptionsMonitor监听配置变更，在每次使用HttpClient前手动更新BaseAddress：

1. 先注册HttpClient（无需在注册时设置BaseAddress）：

builder.Services.AddHttpClient("GitHub")
    .ConfigureHttpClient(httpClient =>
    {
        // 配置不需要动态变更的请求头
        httpClient.DefaultRequestHeaders.Add(HeaderNames.Accept, "application/vnd.github.v3+json");
        httpClient.DefaultRequestHeaders.Add(HeaderNames.UserAgent, "HttpRequestsSample");
    });

2. 在使用HttpClient的服务/函数中，注入IHttpClientFactory和IOptionsMonitor<AppConfigSettings>（AppConfigSettings是绑定App Config配置的实体类）：

private readonly IHttpClientFactory _httpClientFactory;
private readonly IOptionsMonitor<AppConfigSettings> _appConfigMonitor;

public MyFunction(IHttpClientFactory httpClientFactory, IOptionsMonitor<AppConfigSettings> appConfigMonitor)
{
    _httpClientFactory = httpClientFactory;
    _appConfigMonitor = appConfigMonitor;
}

public async Task<IActionResult> Run([HttpTrigger(AuthorizationLevel.Function, "get")] HttpRequest req)
{
    var client = _httpClientFactory.CreateClient("GitHub");
    // 每次请求前读取最新的BaseUrl并设置
    client.BaseAddress = new Uri(_appConfigMonitor.CurrentValue.BaseUrl!);
    
    // 执行请求逻辑
    var response = await client.GetAsync("/repos/dotnet/AspNetCore.Docs/branches");
    // ...
}

方法二：自定义DelegatingHandler统一处理动态BaseAddress #

创建自定义消息处理程序，在每次发送请求前自动应用最新的BaseUrl，无需修改业务代码：

1. 实现自定义DelegatingHandler：

public class DynamicBaseAddressHandler : DelegatingHandler
{
    private readonly IOptionsMonitor<AppConfigSettings> _appConfigMonitor;

    public DynamicBaseAddressHandler(IOptionsMonitor<AppConfigSettings> appConfigMonitor)
    {
        _appConfigMonitor = appConfigMonitor;
    }

    protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
    {
        var latestBaseUrl = _appConfigMonitor.CurrentValue.BaseUrl!;
        // 处理相对路径的请求，自动拼接最新的BaseAddress
        if (request.RequestUri != null && !request.RequestUri.IsAbsoluteUri)
        {
            request.RequestUri = new Uri(new Uri(latestBaseUrl), request.RequestUri);
        }
        // 如果没有设置BaseAddress，直接赋值最新的
        else if (request.BaseAddress == null)
        {
            request.BaseAddress = new Uri(latestBaseUrl);
        }

        return await base.SendAsync(request, cancellationToken);
    }
}

2. 注册Handler和HttpClient：

// 注册自定义Handler
builder.Services.AddTransient<DynamicBaseAddressHandler>();

builder.Services.AddHttpClient("GitHub")
    .AddHttpMessageHandler<DynamicBaseAddressHandler>()
    .ConfigureHttpClient(httpClient =>
    {
        // 配置固定请求头
        httpClient.DefaultRequestHeaders.Add(HeaderNames.Accept, "application/vnd.github.v3+json");
        httpClient.DefaultRequestHeaders.Add(HeaderNames.UserAgent, "HttpRequestsSample");
    });

3. 使用时直接注入HttpClient即可，无需额外处理BaseAddress：

private readonly HttpClient _githubClient;

public MyFunction(IHttpClientFactory httpClientFactory)
{
    _githubClient = httpClientFactory.CreateClient("GitHub");
}

public async Task<IActionResult> Run([HttpTrigger(AuthorizationLevel.Function, "get")] HttpRequest req)
{
    // 直接发送相对路径请求，Handler会自动拼接最新的BaseUrl
    var response = await _githubClient.GetAsync("/repos/dotnet/AspNetCore.Docs/branches");
    // ...
}

前置条件 #

确保你已经正确配置了Azure App Config的动态刷新：

• 在配置App Config时启用了刷新机制（注册需要刷新的配置项并设置缓存过期时间）
• 绑定了AppConfigSettings到对应的配置节
• 在Functions中启用了动态配置刷新（如添加UseAzureAppConfiguration()中间件）

内容的提问来源于stack exchange，提问作者Punter Vicky