Searching and Filtering Log Data
After the CloudWatch Logs agent begins publishing log data to Amazon CloudWatch, you can begin searching and filtering the log data by creating one or more metric filters. Metric filters define the terms and patterns to look for in log data as it is sent to CloudWatch Logs. CloudWatch Logs uses these metric filters to turn log data into CloudWatch metrics that you can graph or set an alarm on.
Filters do not retroactively filter data. Filters only publish the metric data points for events that happen after the filter was created. Filtered results return the first 50 lines, which will not be displayed if the timestamp on the filtered results is earlier than the metric creation time.
Each metric filter is made up of the following key elements:
- filter pattern
A symbolic description of how CloudWatch Logs should interpret the data in each log event. For example, a log entry may contain timestamps, IP addresses, strings, and so on. You use the pattern to specify what to look for in the log file.
- metric name
The name of the CloudWatch metric to which the monitored log information should be published. For example, you may publish to a metric called ErrorCount.
- metric namespace
The destination namespace of the new CloudWatch metric.
- metric value
What to publish to the metric. For example, if you're counting the occurrences of a particular term like "Error", the value will be "1" for each occurrence. If you're counting the bytes transferred the published value will be the value in the log event.