Some nodes shown as offline in a Qlik Sense Enterprise on Windows multi node environment

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A Qlik Sense on-premise installation with multiple nodes shows some of its rim nodes as disconnected. 

The Repository log files show:

Unexpected error in ExistsByID    Read less bytes than expected. Probably the connection was forcefully closed by the remote server.??Read less bytes than expected. Probably the connection was forcefully closed by the remote server.??The underlying provider failed on Open.       at Devart.Common.g.c(Byte[] A_0, Int32 A_1, Int32 A_2)??   at Devart.Common.o.d(Byte[] A_0, Int32 A_1, Int32 A_2)??   at Devart.Data.PostgreSql.i.a(PgSqlConnection A_0)??   at Devart.Data.PostgreSql.i..ctor(PgSqlConnectionOptions A_0, PgSqlConnection A_1)??   at Devart.Data.PostgreSql.ai.a(a2 A_0, Object A_1, DbConnectionBase A_2)??   at Devart.Common.DbConnectionFactory.a(DbConnectionPool A_0, a2 A_1, DbConnectionBase A_2)??   at Devart.Common.DbConnectionPool.a(DbConnectionBase A_0)??   at Devart.Common.DbConnectionPool.GetObject(DbConnectionBase owningConnection)??   at Devart.Common.DbConnectionFactory.b(DbConnectionBase A_0)??   at Devart.Common.DbConnectionClosed.Open(DbConnectionBase outerConnection)??   at Devart.Common.DbConnectionBase.Open()??   at Devart.Data.PostgreSql.PgSqlConnection.Open()??   at System.Data.Entity.Infrastructure.Interception.InternalDispatcher`1.Dispatch[TTarget,TInterceptionContext](TTarget target, Action`2 operation, TInterceptionContext interceptionContext, Action`3 executing, Action`3 executed)??   at System.Data.Entity.Infrastructure.Interception.DbConnectionDispatcher.Open(DbConnection connection, DbInterceptionContext interceptionContext)??   at System.Data.Entity.Core.EntityClient.EntityConnection.Open()??   at System.Data.Entity.Core.EntityClient.EntityConnection.Open()??   at System.Data.Entity.Core.Objects.ObjectContext.EnsureConnection(Boolean shouldMonitorTransactions)??   at System.Data.Entity.Core.Objects.ObjectContext.ExecuteInTransaction[T](Func`1 func, IDbExecutionStrategy executionStrategy, Boolean startLocalTransaction, Boolean releaseConnectionOnSuccess)??   at System.Data.Entity.Core.Objects.ObjectQuery`1.<>c__DisplayClass7.<GetResults>b__5()??   at System.Data.Entity.Core.Objects.ObjectQuery`1.GetResults(Nullable`1 forMergeOption)??   at System.Data.Entity.Core.Objects.ObjectQuery`1.<System.Collections.Generic.IEnumerable<T>.GetEnumerator>b__0()??   at System.Data.Entity.Internal.LazyEnumerator`1.MoveNext()??   at System.Linq.Enumerable.Single[TSource](IEnumerable`1 source)??   at Repository.Core.Repository.Common.EntityTransactionRepository.ExistsById[T](Guid id)??   at Repository.Core.Repository.Common.ModelRepository`1.ExistsByID(Guid id)        0d2b189c-60c1-4466-9e24-218ad77a913b

Environment:

• Qlik Sense Enterprise on Windows 

An external Load Balancer may have its max connections set too low or Qlikl Sense was not configured to allow for the required connections. 

Resolution:

Increase the max allowed connections as documented in: PostgreSQL: postgresql.conf and pg_hba.conf explained.

For external load balancer, steps will need to be obtained from the vendor.