Tail an AWS CloudWatch Log Group

I'm having the same problem. If you are using CloudFormation to deploy your instances and/or log streams, the best way I have found to do this is by appending a reference to your instance ID at the end of your metric name.

"MetricTransformations": [
{
    "MetricValue": "1",
    "MetricNamespace": "myNamespace",
    "MetricName": { "Fn::Join": [ "", [ "myMetric - ", { "Ref" : "InstanceID" }] ] }
}

What would be nice is if you could somehow associate your logstreams as a dimension in a single metric, rather than creating one for each instance.

The filter doesn't work like what you want. You can't filter based on log stream, only on log line content.

I suggest you have no filter (eg so the Lambda receives all log events) and check the log stream in the event metadata when your Lambda is invoked. Details on the event format are in the Lambda docs:

https://docs.aws.amazon.com/lambda/latest/dg/services-cloudwatchlogs.html