Considerations for custom metrics in a predictive scaling policy

If an error message is provided, read the message and resolve the issue it reports, if possible.

If an issue occurs when you are trying to use a search expression in a blue/green deployment scenario, first make sure that you understand how to create a search expression that looks for a partial match instead of an exact match. Also, check that your query finds only the Auto Scaling groups that are running the specific application. For more information about the search expression syntax, see CloudWatch search expression syntax in the Amazon CloudWatch User Guide.

If you did not validate an expression in advance, the put-scaling-policy command validates it when you create your scaling policy. However, there is a possibility that this command might fail to identify the exact cause of the detected errors. To fix the issues, troubleshoot the errors that you receive in a response from a request to the get-metric-data command. You can also troubleshoot the expression from the CloudWatch console.

When you view your Load and Capacity graphs in the console, the Capacity graph might not show any data. To ensure that the graphs have complete data, make sure that you consistently enable group metrics for your Auto Scaling groups. For more information, see Enable Auto Scaling group metrics (console).

The capacity metric specification is only useful for blue/green deployments when you have applications that run in different Auto Scaling groups over their lifetime. This custom metric lets you provide the total capacity of multiple Auto Scaling groups. Predictive scaling uses this to show historical data in the Capacity graphs in the console.

You must specify false for ReturnData if MetricDataQueries specifies the SEARCH() function on its own without a math function like SUM(). This is because search expressions might return multiple time series, and a metric specification based on an expression can return only one time series.

All metrics involved in a search expression should be of the same resolution.