为什么我的 Serilog PostgreSQL 接收器在部署到 AWS Lambda 时不写入？

Question

I have a .NET Core API that uses Serilog for logging. When deployed to AWS Lambda, the Console sink works perfectly and writes all messages to AWS CloudWatch .

I also have a PostgreSQL sink (Serilog.Sinks.Postgresql.Alternative) which writes to an AWS database. This works perfectly from my local dev machine. However, when I push it to my AWS Lambda, the database is not getting written to.

• I'm using the exact same database and connection string.
• I'm using the exact same DB user.
• I can successfully write to the DB from my DAL--apart from logging.

This is in my Program.Main .

Log.Logger = new LoggerConfiguration()
    .MinimumLevel.Information()
    .MinimumLevel.Override("Microsoft", LogEventLevel.Warning)
    .MinimumLevel.Override("System", LogEventLevel.Warning)
    .Enrich.FromLogContext()
    .WriteTo.Console()
    .WriteTo.PostgreSQL(connectionString, TableName, columnWriters)
    .CreateLogger();

What am I missing? Maybe it's not flushing the cache on each HTTP request?

UPDATE: I created a custom .NET Core ILogger, and it has the same behavior. That is, it works locally, but not when deployed to my Lambda.

Answer 1

Depending on how your code is structured, if you have a separate Lambda entry point class, your Program.Main is skipped (it's only called when you run dotnet run , thus why it works locally).

You will need to configure the logging in the Lambda entry point class. For example:

    public class LambdaEntryPoint : APIGatewayHttpApiV2ProxyFunction
    {
        protected override void Init(IWebHostBuilder builder)
        {
            Log.Logger = new LoggerConfiguration()
                 .MinimumLevel.Information()
                 .MinimumLevel.Override("Microsoft", LogEventLevel.Warning)
                 .MinimumLevel.Override("System", LogEventLevel.Warning)
                 .Enrich.FromLogContext()
                 .WriteTo.Console() 
                 .WriteTo.PostgreSQL(connectionString, TableName, columnWriters)
                 .CreateLogger();

            builder.UseStartup<Startup>().UseSerilog();
        }
    }

You might find this also doesn't work, the reason being the logs need to be flushed, but you cannot use CloseAndFlush in a lambda, as that closes the stream and there will be no logs on next invocation. Logs to the Console, however, do not need to be flushed.

A solution would be to log to Console, so the logs go to CloudWatch, and then create a Lambda Function triggered by CloudWatch logs for your service, and send them to your PostgreSQL. Here is an example of a Node.js Lambda function for forwarding logs to Seq .

Hope this helps!