在 AWS Lambas 中使用 slf4j（和 io.symphonia:lambda-logging）记录时 CloudWatch 输出中的新行问题

Question

I have the problem, that when logging with slf4j (and io.symphonia:lambda-logging) in Java, for every new line in the logging message CloudWatch outputs a new log message. This also happens for exceptions using the LOGGER.error(String msg, Throwable t) )

And since the messages output by CloudWatch are unsorted and multiple messages can come in from different Lambdas (or other Services, etc.) the logs are becoming unreadable.

Answer 1

One solution to this is to setup the logging pattern in the logging configuration as follows:

<?xml version="1.0" encoding="UTF-8"?>
<configuration packages="com.amazonaws.services.lambda.runtime.log4j2">
  <appender name="Lambda" class="io.symphonia.lambda.logging.DefaultConsoleAppender">
    <encoder>
      <pattern>%date{yyyy-MM-dd HH:mm:ss} %-5level - %logger{0}:%line: %replace(%msg){'\n','&#xd;'} %replace(%exception){'\n','&#xd;'} %nopexception %n</pattern>
    </encoder>
  </appender>

  <root level="info">
    <appender-ref ref="Lambda" />
  </root>
</configuration>

See the <pattern> tag: The magic is in the %replace(%msg){'\n','
'} and the %replace(%exception){'\n','
'} %nopexception . Both calls are replacing the new line (\n) with a carriage return ( ) for the log message (%msg) and a passed in exception (%exception). The reason why the second argument is in Unicode Hex Character Code and the first isn't is described in the conversation on GitHub linked below. I put this into a loggerconfig.xml and setup the logger to use it in the class that is the entry point for the lambda like this:

private static final Logger LOGGER;

  static {
    // must be set before the very first call to LoggerFactory.getLogger()
    System.setProperty(ContextInitializer.CONFIG_FILE_PROPERTY, "loggerconfig.xml");
    LOGGER = LoggerFactory.getLogger(ClassThatShallLog.class);
  }

I came to this solution through this conversation on GitHub.

Answer 2

Use multi_line_start_pattern http://docs.aws.amazon.com/AmazonCloudWatch/latest/DeveloperGuide/AgentReference.html . You can set it to be your timestamp, in which case you will get the desired behavior: