要解决在AWS CloudWatch上无服务器日志不起作用的问题，可以按照以下步骤进行操作：

1. 确保您的无服务器应用程序已正确配置以将日志发送到AWS CloudWatch。您可以使用以下示例代码检查无服务器应用程序是否正确配置。

const AWS = require('aws-sdk');

exports.handler = async (event, context) => {
  const cloudWatchLogs = new AWS.CloudWatchLogs();

  const logGroupName = '/aws/lambda/your-lambda-function-name';
  const logStreamName = 'your-log-stream-name';

  const logData = 'Your log data';

  const params = {
    logGroupName: logGroupName,
    logStreamName: logStreamName,
    logEvents: [
      {
        message: logData,
        timestamp: new Date().getTime()
      }
    ]
  };

  try {
    await cloudWatchLogs.putLogEvents(params).promise();
    console.log('Log data sent to CloudWatch successfully');
  } catch (error) {
    console.error('Failed to send log data to CloudWatch', error);
  }
};

请确保将your-lambda-function-name替换为您的Lambda函数的名称，将your-log-stream-name替换为您的日志流的名称，以及将Your log data替换为您要发送的日志数据。

2. 确保您的无服务器应用程序具有适当的IAM角色权限来将日志发送到CloudWatch。您可以为您的Lambda函数附加一个具有以下权限的IAM角色。

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Action": [
        "logs:CreateLogGroup",
        "logs:CreateLogStream",
        "logs:PutLogEvents"
      ],
      "Resource": "arn:aws:logs:*:*:*"
    }
  ]
}

这将为Lambda函数提供创建日志组、创建日志流和将日志事件发送到CloudWatch的权限。

3. 检查AWS CloudWatch日志组和日志流是否存在。您可以使用以下示例代码检查日志组和日志流是否存在。

const AWS = require('aws-sdk');

exports.handler = async (event, context) => {
  const cloudWatchLogs = new AWS.CloudWatchLogs();

  const logGroupName = '/aws/lambda/your-lambda-function-name';
  const logStreamName = 'your-log-stream-name';

  const params = {
    logGroupNamePrefix: logGroupName,
    limit: 1
  };

  try {
    const response = await cloudWatchLogs.describeLogGroups(params).promise();
    const logGroups = response.logGroups;

    const logGroup = logGroups.find(group => group.logGroupName === logGroupName);

    if (logGroup) {
      const logStreamParams = {
        logGroupName: logGroupName,
        logStreamNamePrefix: logStreamName,
        limit: 1
      };

      const logStreamResponse = await cloudWatchLogs.describeLogStreams(logStreamParams).promise();
      const logStreams = logStreamResponse.logStreams;

      const logStream = logStreams.find(stream => stream.logStreamName === logStreamName);

      if (logStream) {
        console.log('Log group and log stream exist');
      } else {
        console.error('Log stream does not exist');
      }
    } else {
      console.error('Log group does not exist');
    }
  } catch (error) {
    console.error('Failed to describe log groups and log streams', error);
  }
};

请确保将your-lambda-function-name替换为您的Lambda函数的名称，并将your-log-stream-name替换为您要检查的日志流的名称。

如果您发现日志组或日志流不存在，您可以使用AWS管理控制台或AWS CLI手动创建它们。

通过检查这些步骤，您应该能够解决在AWS CloudWatch上无服务器日志不起作用的问题。