EKS Auto Mode MTU Value

In EKS Auto Mode, you don't have direct access to modify the worker nodes as they are managed by AWS. The nodes are indeed immutable, which means you can't make changes to them directly after they're launched.

However, EKS Auto Mode is designed to handle most infrastructure components automatically, including network configurations. The MTU (Maximum Transmission Unit) value is typically set to an optimal value by default for the network interfaces on the EKS nodes.

If you need to customize the MTU value, you have a few options:

1. Node Class Configuration: You might be able to specify network-related parameters when creating a Node Class for your EKS Auto Mode cluster. This could potentially include MTU settings, although it's not explicitly mentioned in the available documentation.

2. Custom Launch Template: While Auto Mode doesn't allow for custom AMIs, there might be options to use a custom launch template that could include network configurations.

3. CNI Plugin Configuration: The Amazon VPC CNI plugin, which is automatically managed in Auto Mode, might have options to configure MTU values. You'd need to check the latest documentation for any available customization options.

4. Support Case: If you have a specific requirement for MTU settings that isn't met by the default configuration, it's recommended to open a support case with AWS. They can investigate and potentially provide a solution or workaround specific to your use case.

Remember that one of the main benefits of EKS Auto Mode is simplified management, where AWS handles many of the low-level configurations. If you find yourself needing extensive customization of node-level settings like MTU, you might want to consider if a standard EKS setup with managed node groups would be more suitable for your needs, as it provides more flexibility in node configuration.
Sources
eks auto mode - custom amis | AWS re:Post
Configure EKS Auto Mode settings - Amazon EKS