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Using Lambda with CloudWatch Logs

You can use a Lambda function to monitor and analyze logs from an Amazon CloudWatch Logs log stream. Create subscriptions for one or more log streams to invoke a function when logs are created or match an optional pattern. Use the function to send a notification or persist the log to a database or storage.

CloudWatch Logs invokes your function asynchronously with an event that contains log data. The value of the data field is a Base64-encoded .zip file archive.

Example CloudWatch Logs message event

{
  "awslogs": {
    "data": "ewogICAgIm1lc3NhZ2VUeXBlIjogIkRBVEFfTUVTU0FHRSIsCiAgICAib3duZXIiOiAiMTIzNDU2Nzg5MDEyIiwKICAgICJsb2dHcm91cCI6I..."
  }
}

When decoded and decompressed, the log data is a JSON document with the following structure:

Example CloudWatch Logs message data (decoded)

{
    "messageType": "DATA_MESSAGE",
    "owner": "123456789012",
    "logGroup": "/aws/lambda/echo-nodejs",
    "logStream": "2019/03/13/[$LATEST]94fa867e5374431291a7fc14e2f56ae7",
    "subscriptionFilters": [
        "LambdaStream_cloudwatchlogs-node"
    ],
    "logEvents": [
        {
            "id": "34622316099697884706540976068822859012661220141643892546",
            "timestamp": 1552518348220,
            "message": "REPORT RequestId: 6234bffe-149a-b642-81ff-2e8e376d8aff\tDuration: 46.84 ms\tBilled Duration: 47 ms \tMemory Size: 192 MB\tMax Memory Used: 72 MB\t\n"
        }
    ]
}

For a sample application that uses CloudWatch Logs as a trigger, see Error processor sample application for AWS Lambda.