.NET 5升级.NET 7部署Ubuntu后connectionString为空异常求助

我已将API从.NET 5升级至.NET 7并部署到Ubuntu 23.04服务器，本地环境下API与数据库连接正常且可处理请求，但部署到服务器后，程序无法读取appsettings.json中的connectionString，启动时抛出异常：

Unhandled exception. System.ArgumentNullException: Value cannot be null. (Parameter 'connectionString')

相关配置与代码 #

appsettings.json #

{
    "AppSettings": {
        "Secret": "*************",
        "EmailFrom": "********",
        "SmtpHost": "v******",
        "SmtpPort": 587,
        "SmtpUser": "a*****",
        "SmtpPass": "HJu******"
    },

  "ConnectionStrings": {
    "WebApiDatabase": "Data Source=WebApiDatabase.db",
    "HangfireConnection": "Server=**.**.***.***;Port=5432;Database=Min;User Id=postgres;Password=min***;" //server
    //"HangfireConnection": "Host=localhost;Port=5432;Database=Min;User Id=postgres;Password=*****;" // local
  },

    "Logging": {
      "LogLevel": {
        "Default": "Information",
        "Microsoft": "Warning",
        "Microsoft.Hosting.Lifetime": "Information",
        "Hangfire": "Information"
      } 
    },

    "AllowedHosts": "*",

  "postgresqlconnection": {
    "connectionString": "Server=**.**.***.***;Port=5432;Database=Min;User Id=postgres;Password=min***;" //server
    //"connectionString": "Host=localhost;Port=5432;Database=Min;User Id=postgres;Password=*****;" // local
  },

    "mongoconnection": {
        "connectionString": "mongodb://localhost:27017/?readPreference=primary&appname=MongoDB%20Compass%20Community&ssl=false",
        "database": "backlog",
        "collection": "rawData",
        "collectionpMedian": "resultPmedian",
        "collectionClustering": "resultClustering"
    },

    "urlSettings": {
        "staticPageUrl": "http://**.**.***.***",
        "backendUrl": "http://**.**.***.***"
    },

    "variousSettings": {
        "defaultMessage": "A default message if nothing is found in the database."
    }
}

Startup.cs #

services.AddHangfire(configuration => configuration
                .SetDataCompatibilityLevel(CompatibilityLevel.Version_170)
                .UseSimpleAssemblyNameTypeSerializer()
                .UseRecommendedSerializerSettings()
                .UsePostgreSqlStorage(Configuration.GetConnectionString("HangfireConnection")));

DataContext.cs #

private readonly IConfiguration Configuration;

public DataContext(IConfiguration configuration)
{
    Configuration = configuration;
}

protected override void OnConfiguring(DbContextOptionsBuilder options)
{
    // connect to postgress database
    var connectionString = Configuration["postgresqlconnection:connectionString"];

    options.UseNpgsql(connectionString);
}

完整错误日志 #

root@ubuntu-4gb:/# /usr/bin/dotnet /var/www/MinAPI/MinWebApi.dll
Unhandled exception. System.ArgumentNullException: Value cannot be null. (Parameter 'connectionString')
   at Hangfire.PostgreSql.PostgreSqlStorage..ctor(String connectionString, Action`1 connectionSetup, PostgreSqlStorageOptions options)
   at Hangfire.PostgreSql.PostgreSqlBootstrapperConfigurationExtensions.UsePostgreSqlStorage(IGlobalConfiguration configuration, String connectionString, Action`1 connectionSetup, PostgreSqlStorageOptions options)
   at Hangfire.PostgreSql.PostgreSqlBootstrapperConfigurationExtensions.UsePostgreSqlStorage(IGlobalConfiguration configuration, String connectionString)
   at WebApi.Startup.<ConfigureServices>b__4_2(IGlobalConfiguration configuration) in D:\C Sharp\Startup.cs:line 46
   at Hangfire.HangfireServiceCollectionExtensions.<>c__DisplayClass0_0.<AddHangfire>b__0(IServiceProvider provider, IGlobalConfiguration config)
   at Hangfire.HangfireServiceCollectionExtensions.<>c__DisplayClass1_0.<AddHangfire>b__14(IServiceProvider serviceProvider)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitFactory(FactoryCallSite factoryCallSite, RuntimeResolverContext context)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitRootCache(ServiceCallSite callSite, RuntimeResolverContext context)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor`2.VisitCallSite(ServiceCallSite callSite, TArgument argument)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.Resolve(ServiceCallSite callSite, ServiceProviderEngineScope scope)
   at Microsoft.Extensions.DependencyInjection.ServiceProvider.CreateServiceAccessor(Type serviceType)
   at System.Collections.Concurrent.ConcurrentDictionary`2.GetOrAdd(TKey key, Func`2 valueFactory)
   at Microsoft.Extensions.DependencyInjection.ServiceProvider.GetService(Type serviceType, ServiceProviderEngineScope serviceProviderEngineScope)
   at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetService[T](IServiceProvider provider)
   at Hangfire.HangfireServiceCollectionExtensions.ThrowIfNotConfigured(IServiceProvider serviceProvider)
   at Hangfire.HangfireServiceCollectionExtensions.CreateBackgroundJobServerHostedService(IServiceProvider provider, JobStorage storage, IEnumerable`1 additionalProcesses, BackgroundJobServerOptions options)
   at Hangfire.HangfireServiceCollectionExtensions.<>c__DisplayClass9_0.<AddHangfireServerInner>b__0(IServiceProvider provider)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitFactory(FactoryCallSite factoryCallSite, RuntimeResolverContext context)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitDisposeCache(ServiceCallSite transientCallSite, RuntimeResolverContext context)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor`2.VisitCallSite(ServiceCallSite callSite, TArgument argument)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitIEnumerable(IEnumerableCallSite enumerableCallSite, RuntimeResolverContext context)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor`2.VisitNoCache(ServiceCallSite callSite, TArgument argument)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor`2.VisitCallSite(ServiceCallSite callSite, TArgument argument)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.Resolve(ServiceCallSite callSite, ServiceProviderEngineScope scope)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.DynamicServiceProviderEngine.<>c__DisplayClass2_0.<RealizeService>b__0(ServiceProviderEngineScope scope)
   at Microsoft.Extensions.DependencyInjection.ServiceProvider.GetService(Type serviceType, ServiceProviderEngineScope serviceProviderEngineScope)
   at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetRequiredService(IServiceProvider provider, Type serviceType)
   at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetRequiredService[T](IServiceProvider provider)
   at Microsoft.Extensions.Hosting.Internal.Host.StartAsync(CancellationToken cancellationToken)
   at Microsoft.Extensions.Hosting.HostingAbstractionsHostExtensions.RunAsync(IHost host, CancellationToken token)
   at Microsoft.Extensions.Hosting.HostingAbstractionsHostExtensions.RunAsync(IHost host, CancellationToken token)
   at Microsoft.Extensions.Hosting.HostingAbstractionsHostExtensions.Run(IHost host)
   at WebApi.Program.Main(String[] args) in D:\C Sharp\Program.cs:line 12

已尝试的解决方法 #

• 硬编码连接字符串
• 修改变量名
• 同步appsettings.Development.json
  仅同步配置后短暂正常，但重启服务后异常复现。

解决方案 #

1. 检查appsettings.json的部署状态 #

• 确认服务器/var/www/MinAPI/目录下存在正确的appsettings.json，内容与本地测试版本一致（重点核对HangfireConnection和postgresqlconnection节点）。
• 修复文件权限，确保dotnet进程可读取：

  sudo chmod 644 /var/www/MinAPI/appsettings.json
  sudo chown www-data:www-data /var/www/MinAPI/appsettings.json
  

2. 验证环境配置加载逻辑 #

.NET在Linux环境下优先加载环境特定配置文件（如appsettings.Production.json），若该文件存在且未配置对应连接字符串，会覆盖默认配置：

• 检查服务器是否存在appsettings.Production.json，若存在则补充完整的ConnectionStrings和postgresqlconnection节点。
• 启动时显式指定环境：

  dotnet /var/www/MinAPI/MinWebApi.dll --environment Production
  

  或设置环境变量：

  export ASPNETCORE_ENVIRONMENT=Production
  dotnet /var/www/MinAPI/MinWebApi.dll
  

3. 修复配置读取方式 #

• 对DataContext的配置读取添加空值检查，改用更可靠的Section读取：

  var connectionString = Configuration.GetSection("postgresqlconnection").GetValue<string>("connectionString");
  if(string.IsNullOrEmpty(connectionString))
  {
      throw new InvalidOperationException("PostgreSQL connection string is not configured.");
  }
  options.UseNpgsql(connectionString);
  

• 对Hangfire配置同样添加空值验证：

  var hangfireConn = Configuration.GetConnectionString("HangfireConnection");
  if(string.IsNullOrEmpty(hangfireConn))
  {
      throw new InvalidOperationException("Hangfire connection string is not configured.");
  }
  services.AddHangfire(configuration => configuration
          .SetDataCompatibilityLevel(CompatibilityLevel.Version_170)
          .UseSimpleAssemblyNameTypeSerializer()
          .UseRecommendedSerializerSettings()
          .UsePostgreSqlStorage(hangfireConn));
  

4. 检查发布模式与文件包含 #

• 在Visual Studio中右键appsettings.json，设置属性→复制到输出目录→选择“始终复制”，确保发布时文件被包含到输出目录。
• 确认发布后的bin/Release/net7.0/publish/目录中存在appsettings.json，再将该目录完整部署到服务器。

5. 排查环境变量覆盖问题 #

.NET配置加载顺序为：环境变量→命令行参数→环境特定配置文件→默认配置文件，若服务器存在同名环境变量会覆盖连接字符串：

• 检查环境变量：

  printenv | grep ConnectionStrings
  

• 若存在相关变量，临时取消设置：

  unset ConnectionStrings__HangfireConnection
  

内容的提问来源于stack exchange，提问作者Bashar Al-shaibani