The retirement date of May 31st, 2024 means that after this date, the Container insights recommended alerts (custom metrics) (preview) will no longer work. This means that any existing alerts that are based on these custom metrics will stop working after this date.
Regarding your second question, I'm afraid that the retirement date is not something that can be extended. However, I would recommend that your customer start planning for the migration of their alerts as soon as possible to ensure a smooth transition. They can refer to the Azure Monitor documentation for guidance on how to migrate their alerts to the new offering. If they have any specific questions or concerns, they can also reach out to Microsoft support for assistance.
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