Azure Function App访问提示Function host is not running问题排查

问题现象 #

• 项目本地调试运行完全正常，CI/CD构建、发布流水线全部执行成功，新建Function App重新部署后问题仍未解决
• 已通过Application Insights、Azure门户函数服务面板查看日志，确认存在「Function host is not running」报错
• 报错参考截图：
  
• 问题项目原有Startup.cs配置逻辑如下：

public override void Configure(IFunctionsHostBuilder builder)
{
    //var connectionString = Environment.GetEnvironmentVariable("ConnectionStrings:DBConnection");

    var serviceProvider = builder.Services.BuildServiceProvider();
    _configuration = serviceProvider.GetRequiredService<IConfiguration>();
    var appSettingsSection = _configuration.GetSection("AppSettings");
    builder.Services.Configure<AppSettings>(appSettingsSection);
    var appSettings = appSettingsSection.Get<AppSettings>();
    RuntimeConfig.appsettings = appSettings;

    var ConnectionString = RuntimeConfig.appsettings.AppDBConnection;
    ///builder.Services.AddDbContext<ShardingDbContext>(options => options.UseSqlServer(ConnectionString), ServiceLifetime.Transient);
    //builder.Services.AddScoped<ITestService, TestService>();
}

public override void ConfigureAppConfiguration(IFunctionsConfigurationBuilder builder)
{
    FunctionsHostBuilderContext context = builder.GetContext();

    builder.ConfigurationBuilder
        .AddJsonFile(Path.Combine(context.ApplicationRootPath, "local.settings.json"), optional: true, reloadOnChange: false)
        .AddJsonFile(Path.Combine(context.ApplicationRootPath, $"{context.EnvironmentName}.settings.json"), optional: true, reloadOnChange: false)
        .AddEnvironmentVariables();
}

问题根因 #

1. 核心触发点：在Configure方法中手动调用builder.Services.BuildServiceProvider()会生成独立于Azure Functions运行时根容器的服务提供器副本，造成容器冲突，云端生产环境运行时会在启动阶段直接抛出致命错误，导致Function Host无法启动。本地调试用的Core Tools校验规则较宽松，不会拦截该操作，因此本地运行正常。
2. 配置读取逻辑不规范：通过手动构建的服务提供器获取IConfiguration实例，会出现配置加载顺序异常，且local.settings.json默认不会随发布流程上传到云端，很容易出现配置缺失触发空引用，进一步导致Host启动失败。

修复步骤 #

• 移除Configure方法中手动调用BuildServiceProvider()的逻辑，直接通过Functions运行时上下文获取IConfiguration实例，避免容器冲突
• 修正配置绑定逻辑，不需要提前构建容器即可完成配置读取与绑定
• 所有云端运行所需的配置项，不要依赖本地json文件，需要在Azure Function App门户的「配置-应用程序设置」面板中手动添加，层级配置用:分隔即可（例如AppSettings:AppDBConnection），运行时会自动加载到IConfiguration中

修正后的Startup.cs代码如下：

public override void Configure(IFunctionsHostBuilder builder)
{
    // 直接从运行时上下文获取配置，无需手动构建服务提供器
    var executionContext = builder.GetContext();
    IConfiguration configuration = executionContext.Configuration;
    
    var appSettingsSection = configuration.GetSection("AppSettings");
    builder.Services.Configure<AppSettings>(appSettingsSection);
    // 直接从配置节绑定实例，不需要从服务容器解析
    var appSettings = appSettingsSection.Get<AppSettings>();
    RuntimeConfig.appsettings = appSettings;

    var connectionString = appSettings.AppDBConnection;
    // 按需取消注释注册服务即可
    // builder.Services.AddDbContext<ShardingDbContext>(options => options.UseSqlServer(connectionString), ServiceLifetime.Transient);
    // builder.Services.AddScoped<ITestService, TestService>();
}

public override void ConfigureAppConfiguration(IFunctionsConfigurationBuilder builder)
{
    FunctionsHostBuilderContext context = builder.GetContext();

    builder.ConfigurationBuilder
        .AddJsonFile(Path.Combine(context.ApplicationRootPath, "local.settings.json"), optional: true, reloadOnChange: false)
        .AddJsonFile(Path.Combine(context.ApplicationRootPath, $"{context.EnvironmentName}.settings.json"), optional: true, reloadOnChange: false)
        .AddEnvironmentVariables();
}

验证方式 #

• 替换上述修正后的代码，重新通过流水线发布
• 检查Azure Function App配置面板，确认所有需要的应用设置都已正确添加
• 重启Function App，等待2-3分钟待宿主完全启动后，再访问函数URL即可正常响应

注意：如果重启后仍有报错，可以在Kudu站点中查看D:\home\LogFiles\Application\Functions\Host目录下的宿主日志，会打印具体的启动失败堆栈信息方便进一步排查。

内容的提问来源于stack exchange，提问作者Md Aslam