swagger提示Instance failure

场景：abp发布到iis后，发现访问链接数据库的接口，都返回如下：

1 {
2   "Code": 1,
3   "Message": "Instance failure.",
4   "Success": false,
5   "Timestamp": 1624431552715
6 }

初步分析：显示实例错误，但是发布前明明测试了一下，没错误，就检查了一下appsettings.json，数据库字符串正确，翻看了一下abp的日志，如下：

 1 2021-06-23 14:41:00.254 +08:00 [ERR] Instance failure.
 2 System.InvalidOperationException: Instance failure.
 3    at Microsoft.Data.ProviderBase.DbConnectionPool.TryGetConnection(DbConnection owningObject, UInt32 waitForMultipleObjectsTimeout, Boolean allowCreate, Boolean onlyOneCheckConnection, DbConnectionOptions userOptions, DbConnectionInternal& connection)
 4    at Microsoft.Data.ProviderBase.DbConnectionPool.TryGetConnection(DbConnection owningObject, TaskCompletionSource`1 retry, DbConnectionOptions userOptions, DbConnectionInternal& connection)
 5    at Microsoft.Data.ProviderBase.DbConnectionFactory.TryGetConnection(DbConnection owningConnection, TaskCompletionSource`1 retry, DbConnectionOptions userOptions, DbConnectionInternal oldConnection, DbConnectionInternal& connection)
 6    at Microsoft.Data.ProviderBase.DbConnectionInternal.TryOpenConnectionInternal(DbConnection outerConnection, DbConnectionFactory connectionFactory, TaskCompletionSource`1 retry, DbConnectionOptions userOptions)
 7    at Microsoft.Data.SqlClient.SqlConnection.TryOpen(TaskCompletionSource`1 retry, SqlConnectionOverrides overrides)
 8    at Microsoft.Data.SqlClient.SqlConnection.OpenAsync(CancellationToken cancellationToken)
 9 --- End of stack trace from previous location ---
10    at Microsoft.EntityFrameworkCore.Storage.RelationalConnection.OpenInternalAsync(Boolean errorsExpected, CancellationToken cancellationToken)
11    at Microsoft.EntityFrameworkCore.Storage.RelationalConnection.OpenInternalAsync(Boolean errorsExpected, CancellationToken cancellationToken)
12    at Microsoft.EntityFrameworkCore.Storage.RelationalConnection.OpenAsync(CancellationToken cancellationToken, Boolean errorsExpected)
13    at Microsoft.EntityFrameworkCore.Storage.RelationalCommand.ExecuteReaderAsync(RelationalCommandParameterObject parameterObject, CancellationToken cancellationToken)
14    at Microsoft.EntityFrameworkCore.Query.Internal.SplitQueryingEnumerable`1.AsyncEnumerator.InitializeReaderAsync(DbContext _, Boolean result, CancellationToken cancellationToken)
15    at Microsoft.EntityFrameworkCore.SqlServer.Storage.Internal.SqlServerExecutionStrategy.ExecuteAsync[TState,TResult](TState state, Func`4 operation, Func`4 verifySucceeded, CancellationToken cancellationToken)
16    at Microsoft.EntityFrameworkCore.Query.Internal.SplitQueryingEnumerable`1.AsyncEnumerator.MoveNextAsync()
17    at Microsoft.EntityFrameworkCore.EntityFrameworkQueryableExtensions.ToListAsync[TSource](IQueryable`1 source, CancellationToken cancellationToken)
18    at Microsoft.EntityFrameworkCore.EntityFrameworkQueryableExtensions.ToListAsync[TSource](IQueryable`1 source, CancellationToken cancellationToken)
19    at Volo.Abp.BackgroundJobs.EntityFrameworkCore.EfCoreBackgroundJobRepository.GetWaitingListAsync(Int32 maxResultCount)
20    at Castle.DynamicProxy.AsyncInterceptorBase.ProceedAsynchronous[TResult](IInvocation invocation, IInvocationProceedInfo proceedInfo)
21    at Volo.Abp.Castle.DynamicProxy.CastleAbpMethodInvocationAdapterWithReturnValue`1.ProceedAsync()
22    at Volo.Abp.Uow.UnitOfWorkInterceptor.InterceptAsync(IAbpMethodInvocation invocation)
23    at Volo.Abp.Castle.DynamicProxy.CastleAsyncAbpInterceptorAdapter`1.InterceptAsync[TResult](IInvocation invocation, IInvocationProceedInfo proceedInfo, Func`3 proceed)
24    at Volo.Abp.BackgroundJobs.BackgroundJobStore.GetWaitingJobsAsync(Int32 maxResultCount)
25    at Volo.Abp.BackgroundJobs.BackgroundJobWorker.DoWorkAsync(PeriodicBackgroundWorkerContext workerContext)
26    at Volo.Abp.BackgroundWorkers.AsyncPeriodicBackgroundWorkerBase.DoWorkAsync()