How can I design a cloudwatch logs filter?

In the context of AWS, you can design a cloud watch logs filter for the task of monitoring logs generated by EC2 Instance by using the following steps which are given below:-

Define log group

Try to ensure that the logs which are generated by your EC2 instance are stored in a cloudwatch log group.

Create filter pattern

You can try to construct a filter pattern that would match the log messages that contain specific keywords or phrases that are relevant to your monitoring requirements.

Test filter pattern

Try to test your filter pattern against sample log messages so that you can ensure that it accurately identifies and extracts the required message.

Apply filter to log group

Try to apply the filter pattern to the log group that contains your EC2 Instance logs. You can create or even update a metric filter by using the Cloudwatch logs console, command line interface, or SDKs the automatically process incoming log messages.

Cloudwatch alerts or metrics

Try to configure cloud watch alarm metrics which are based on the filtered log data for the task of monitoring specific events or even errors. You can use Cloudwatch metrics, logs insights, or other AWS services for visualizing and analyzing the filtered log data in real time.

Here is the simplified example given of how you can create a cloud watch logs filter by using the AWS command line interface:-

Aws logs put-metric-filter 
  --log-group-name /aws/ec2/instance-logs 
  --filter-name ErrorFilter 
  --filter-pattern ‘[ERROR]’ 
  --metric-transformations 
    metricName=ErrorCount,metricNamespace=CustomNamespace,metricValue=1