Kubernetes field management - Amazon EKS
View field management statusUnderstanding field management syntax in the Kubernetes API
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Kubernetes field management

Amazon EKS add-ons are installed to your cluster using standard, best practice configurations. For more information about adding an Amazon EKS add-on to your cluster, see Amazon EKS add-ons.

You may want to customize the configuration of an Amazon EKS add-on to enable advanced features. Amazon EKS uses the Kubernetes server-side apply feature to enable management of an add-on by Amazon EKS without overwriting your configuration for settings that aren't managed by Amazon EKS. For more information, see Server-Side Apply in the Kubernetes documentation. To achieve this, Amazon EKS manages a minimum set of fields for every add-on that it installs. You can modify all fields that aren't managed by Amazon EKS, or another Kubernetes control plane process such as kube-controller-manager, without issue.

Important

Modifying a field managed by Amazon EKS prevents Amazon EKS from managing the add-on and may result in your changes being overwritten when an add-on is updated.

View field management status

You can use kubectl to see which fields are managed by Amazon EKS for any Amazon EKS add-on.

To see the management status of a field

  1. Determine which add-on that you want to examine. To see all of the deployments and DaemonSets deployed to your cluster, see View Kubernetes resources.

  2. View the managed fields for an add-on by running the following command:

    kubectl get type/add-on-name -n add-on-namespace -o yaml

    For example, you can see the managed fields for the CoreDNS add-on with the following command.

    kubectl get deployment/coredns -n kube-system -o yaml

    Field management is listed in the following section in the returned output.

    ...
managedFields:
  - apiVersion: apps/v1
    fieldsType: FieldsV1
    fieldsV1:                        
...
    Note

    If you don't see managedFields in the output, add --show-managed-fields to the command and run it again. The version of kubectl that you're using determines whether managed fields are returned by default.

Understanding field management syntax in the Kubernetes API

When you view details for a Kubernetes object, both managed and unmanaged fields are returned in the output. Managed fields can be either of the following types:

  • Fully managed – All keys for the field are managed by Amazon EKS. Modifications to any value causes a conflict.

  • Partially managed – Some keys for the field are managed by Amazon EKS. Only modifications to the keys explicitly managed by Amazon EKS cause a conflict.

Both types of fields are tagged with manager: eks.

Each key is either a . representing the field itself, which always maps to an empty set, or a string that represents a sub-field or item. The output for field management consists of the following types of declarations:

  • f:name, where name is the name of a field in a list.

  • k:keys, where keys is a map of a list item's fields.

  • v:value, where value is the exact JSON formatted value of a list item.

  • i:index, where index is position of an item in the list.

For more information, see FieldsV1 v1 meta in the Kubernetes documentation.

The following portions of output for the CoreDNS add-on illustrate the previous declarations:

  • Fully managed fields – If a managed field has an f: (field) specified, but no k: (key), then the entire field is managed. Modifications to any values in this field cause a conflict.

    In the following output, you can see that the container named coredns is managed by eks. The args, image, and imagePullPolicy sub-fields are also managed by eks. Modifications to any values in these fields cause a conflict.

    ...
f:containers:
  k:{"name":"coredns"}:
  .: {}
  f:args: {}
  f:image: {}
  f:imagePullPolicy: {}
...
manager: eks
...

  • Partially managed fields – If a managed key has a value specified, the declared keys are managed for that field. Modifying the specified keys cause a conflict.

    In the following output, you can see that eks manages the config-volume and tmp volumes set with the name key.

    ...
f:volumes:
  k:{"name":"config-volume"}:
    .: {}
    f:configMap:
      f:items: {}
      f:name: {}
    f:name: {}
  k:{"name":"tmp"}:
    .: {}
    f:name: {}
...
manager: eks
...

  • Adding keys to partially managed fields – If only a specific key value is managed, you can safely add additional keys, such as arguments, to a field without causing a conflict. If you add additional keys, make sure that the field isn't managed first. Adding or modifying any value that is managed causes a conflict.

    In the following output, you can see that both the name key and name field are managed. Adding or modifying any container name causes a conflict with this managed key. 

    ...
f:containers:
  k:{"name":"coredns"}:
...
    f:name: {}
...
manager: eks
...