Set Serilog minimum level from environment variable

Question

Is it possible to setup Serilog minimum log level from environment variable?

If I try to configure it like this

  "Serilog": {
    "MinimumLevel": "%LOG_LEVEL%",
    "WriteTo": [
      {
        "Name": "RollingFile",
        "Args": {
          "outputTemplate": "{Timestamp:yyyy-MM-dd HH:mm:ss.fff zzz} [{Level}] [v{SourceSystemInformationalVersion}] {Message}{NewLine}{Exception}",
          "pathFormat": "%LOG_FOLDER%/sds-osdr-domain-saga-host-{Date}.log",
          "retainedFileCountLimit": 5
        }
      }
    ]
  }

it returns error

The value %LOG_LEVEL% is not a valid Serilog level.

Is it possible to propagate log level from environment variable somehow?

Answer 1

I think you are asking about configuration by environment which is not specific to serilog.

If the LOG_LEVEL is fixed with the specific environment (development, staging or production), you can set the each LOG_LEVEL in appsettings.<EnvironmentName>.json, and set configuration like this:

var config = new ConfigurationBuilder()
    .SetBasePath(Directory.GetCurrentDirectory())
    .AddJsonFile("appsettings.json", optional: false)
    .AddJsonFile($"appsettings.{env.EnvironmentName}.json", optional: true)
    .Build();

If you need to config the LOG_LEVEL from environment variable in docker-compose file or kubernetes deployment file, then you can read values from environment variables by calling AddEnvironmentVariables:

var config = new ConfigurationBuilder()
    .SetBasePath(Directory.GetCurrentDirectory())
    .AddJsonFile("appsettings.json", optional: false)
    .AddEnvironmentVariables()
    .Build();

And set the environment Serilog:MinimumLevel in windows or ``Serilog__MinimumLevel` in linux and mac.

Answer 2

After some thinking I ended up with the tiny class below

public class EnvironmentVariableLoggingLevelSwitch : LoggingLevelSwitch
{
    public EnvironmentVariableLoggingLevelSwitch(string environmentVariable)
    {
        LogEventLevel level = LogEventLevel.Information;
        if (Enum.TryParse<LogEventLevel>(Environment.ExpandEnvironmentVariables(environmentVariable), true, out level))
        {
            MinimumLevel = level;
        }
    }
}

and using it when configure logger

Log.Logger = new LoggerConfiguration()
    .ReadFrom.Configuration(Configuration)
    .MinimumLevel.ControlledBy(new EnvironmentVariableLoggingLevelSwitch("%LOG_LEVEL%"))
    .CreateLogger();

So, if you don't declare environment variable you still may configure logging level from config file, or override it with environment variable.