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Amazon CloudWatch Logs
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Example: Count Occurrences of a Term

Log events frequently include important messages that you want to count, maybe about the success or failure of operations. For example, an error may occur and be recorded to a log file if a given operation fails. You may want to monitor these entries to understand the trend of your errors.

In the example below, a metric filter is created to monitor for the term Error. The policy has been created and added to the log group MyApp/message.log. CloudWatch Logs publishes a data point to the CloudWatch custom metric ErrorCount in the MyApp/message.log namespace with a value of "1" for every event containing Error. If no event contains the word Error, then no data points are published. When graphing this data in the CloudWatch console, be sure to use the sum statistic.

To create a metric filter using the CloudWatch console

  1. Open the CloudWatch console at https://console.aws.amazon.com/cloudwatch/.

  2. In the navigation pane, choose Logs.

  3. In the contents pane, select a log group, and then choose Create Metric Filter.

  4. On the Define Logs Metric Filter screen, for Filter Pattern, type Error.

    Note

    All entries in Filter Pattern are case-sensitive.

  5. To test your filter pattern, for Select Log Data to Test, select the log group to test the metric filter against, and then choose Test Pattern.

  6. Under Results, CloudWatch Logs displays a message showing how many occurrences of the filter pattern were found in the log file.

    To see detailed results, choose Show test results.

  7. Choose Assign Metric, and then on the Create Metric Filter and Assign a Metric screen, for Filter Name, type MyAppErrorCount.

  8. Under Metric Details, for Metric Namespace, type MyNameSpace.

  9. For Metric Name, type ErrorCount, and then choose Create Filter.

To create a metric filter using the AWS CLI

At a command prompt, run the following command:

aws logs put-metric-filter \
  --log-group-name MyApp/message.log \
  --filter-name MyAppErrorCount \
  --filter-pattern 'Error' \
  --metric-transformations \
      metricName=EventCount,metricNamespace=MyNamespace,metricValue=1

You can test this new policy by posting events containing the word "Error" in the message.

To post events using the AWS CLI

At a command prompt, run the following command. Note that patterns are case-sensitive.

aws logs put-log-events \
  --log-group-name MyApp/access.log --log-stream-name TestStream1 \
  --log-events \
    timestamp=1394793518000,message="This message contains an Error" \
    timestamp=1394793528000,message="This message also contains an Error"