Customizing managed nodes with launch templates - Amazon EKS
Launch template configuration basicsTagging Amazon EC2 instancesUsing custom security groupsAmazon EC2 user dataSpecifying an AMILimits and conditions when specifying an AMI ID

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Customizing managed nodes with launch templates

For the highest level of customization, you can deploy managed nodes using your own launch template. Using a launch template allows capabilities such as the following:

  • Provide bootstrap arguments at deployment of a node, such as extra kubelet arguments.

  • Assign IP addresses to Pods from a different CIDR block than the IP address assigned to the node.

  • Deploy your own custom AMI to nodes.

  • Deploy your own custom CNI to nodes.

When you give your own launch template upon first creating a managed node group, you will also have greater flexibility later. As long as you deploy a managed node group with your own launch template, you can iteratively update it with a different version of the same launch template. When you update your node group to a different version of your launch template, all nodes in the group are recycled to match the new configuration of the specified launch template version.

Managed node groups are always deployed with a launch template to be used with the Amazon EC2 Auto Scaling group. When you don't provide a launch template, the Amazon EKS API creates one automatically with default values in your account. However, we don't recommend that you modify auto-generated launch templates. Furthermore, existing node groups that don't use a custom launch template can't be updated directly. Instead, you must create a new node group with a custom launch template to do so.

Launch template configuration basics

You can create an Amazon EC2 Auto Scaling launch template with the AWS Management Console, AWS CLI, or an AWS SDK. For more information, see Creating a Launch Template for an Auto Scaling group in the Amazon EC2 Auto Scaling User Guide. Some of the settings in a launch template are similar to the settings used for managed node configuration. When deploying or updating a node group with a launch template, some settings must be specified in either the node group configuration or the launch template. Don't specify a setting in both places. If a setting exists where it shouldn't, then operations such as creating or updating a node group fail.

The following table lists the settings that are prohibited in a launch template. It also lists similar settings, if any are available, that are required in the managed node group configuration. The listed settings are the settings that appear in the console. They might have similar but different names in the AWS CLI and SDK.

Launch template – Prohibited Amazon EKS node group configuration
Subnet under Network interfaces (Add network interface) Subnets under Node group network configuration on the Specify networking page
IAM instance profile under Advanced details Node IAM role under Node group configuration on the Configure Node group page
Shutdown behavior and Stop - Hibernate behavior under Advanced details. Retain default Don't include in launch template setting in launch template for both settings. No equivalent. Amazon EKS must control the instance lifecycle, not the Auto Scaling group.

The following table lists the prohibited settings in a managed node group configuration. It also lists similar settings, if any are available, which are required in a launch template. The listed settings are the settings that appear in the console. They might have similar names in the AWS CLI and SDK.

Amazon EKS node group configuration – Prohibited Launch template

(Only if you specified a custom AMI in a launch template) AMI type under Node group compute configuration on Set compute and scaling configuration page – Console displays Specified in launch template and the AMI ID that was specified.

If Application and OS Images (Amazon Machine Image) wasn't specified in the launch template, you can select an AMI in the node group configuration.

Application and OS Images (Amazon Machine Image) under Launch template contents – You must specify an ID if you have either of the following requirements:
Disk size under Node group compute configuration on Set compute and scaling configuration page – Console displays Specified in launch template. Size under Storage (Volumes) (Add new volume). You must specify this in the launch template.
SSH key pair under Node group configuration on the Specify Networking page – The console displays the key that was specified in the launch template or displays Not specified in launch template. Key pair name under Key pair (login).
You can't specify source security groups that are allowed remote access when using a launch template. Security groups under Network settings for the instance or Security groups under Network interfaces (Add network interface), but not both. For more information, see Using custom security groups.
Note

  • If you deploy a node group using a launch template, specify zero or one Instance type under Launch template contents in a launch template. Alternatively, you can specify 0–20 instance types for Instance types on the Set compute and scaling configuration page in the console. Or, you can do so using other tools that use the Amazon EKS API. If you specify an instance type in a launch template, and use that launch template to deploy your node group, then you can't specify any instance types in the console or using other tools that use the Amazon EKS API. If you don't specify an instance type in a launch template, in the console, or using other tools that use the Amazon EKS API, the t3.medium instance type is used. If your node group is using the Spot capacity type, then we recommend specifying multiple instance types using the console. For more information, see Managed node group capacity types.

  • If any containers that you deploy to the node group use the Instance Metadata Service Version 2, make sure to set the Metadata response hop limit to 2 in your launch template. For more information, see Instance metadata and user data in the Amazon EC2 User Guide. If you deploy a managed node group without using a custom launch template, this value is automatically set for the node group in the default launch template.

Tagging Amazon EC2 instances

You can use the TagSpecification parameter of a launch template to specify which tags to apply to Amazon EC2 instances in your node group. The IAM entity calling the CreateNodegroup or UpdateNodegroupVersion APIs must have permissions for ec2:RunInstances and ec2:CreateTags, and the tags must be added to the launch template.

Using custom security groups

You can use a launch template to specify custom Amazon EC2 security groups to apply to instances in your node group. This can be either in the instance level security groups parameter or as part of the network interface configuration parameters. However, you can't create a launch template that specifies both instance level and network interface security groups. Consider the following conditions that apply to using custom security groups with managed node groups:

  • Amazon EKS only allows launch templates with a single network interface specification.

  • By default, Amazon EKS applies the cluster security group to the instances in your node group to facilitate communication between nodes and the control plane. If you specify custom security groups in the launch template using either option mentioned earlier, Amazon EKS doesn't add the cluster security group. So, you must ensure that the inbound and outbound rules of your security groups enable communication with the endpoint of your cluster. If your security group rules are incorrect, the worker nodes can't join the cluster. For more information about security group rules, see Amazon EKS security group requirements and considerations.

  • If you need SSH access to the instances in your node group, include a security group that allows that access.

Amazon EC2 user data

The launch template includes a section for custom user data. You can specify configuration settings for your node group in this section without manually creating individual custom AMIs. For more information about the settings available for Bottlerocket, see Using user data on GitHub.

You can supply Amazon EC2 user data in your launch template using cloud-init when launching your instances. For more information, see the cloud-init documentation. Your user data can be used to perform common configuration operations. This includes the following operations:

Amazon EC2 user data in launch templates that are used with managed node groups must be in the MIME multi-part archive format for Amazon Linux AMIs and TOML format for Bottlerocket AMIs. This is because your user data is merged with Amazon EKS user data required for nodes to join the cluster. Don't specify any commands in your user data that starts or modifies kubelet. This is performed as part of the user data merged by Amazon EKS. Certain kubelet parameters, such as setting labels on nodes, can be configured directly through the managed node groups API.

Note

For more information about advanced kubelet customization, including manually starting it or passing in custom configuration parameters, see Specifying an AMI. If a custom AMI ID is specified in a launch template, Amazon EKS doesn't merge user data.

The following details provide more information about the user data section.

Amazon Linux 2 user data

You can combine multiple user data blocks together into a single MIME multi-part file. For example, you can combine a cloud boothook that configures the Docker daemon with a user data shell script that installs a custom package. A MIME multi-part file consists of the following components:

  • The content type and part boundary declaration – Content-Type: multipart/mixed; boundary="==MYBOUNDARY=="

  • The MIME version declaration – MIME-Version: 1.0

  • One or more user data blocks, which contain the following components:

    • The opening boundary, which signals the beginning of a user data block – --==MYBOUNDARY==

    • The content type declaration for the block: Content-Type: text/cloud-config; charset="us-ascii". For more information about content types, see the cloud-init documentation.

    • The content of the user data (for example, a list of shell commands or cloud-init directives).

    • The closing boundary, which signals the end of the MIME multi-part file: --==MYBOUNDARY==--

    The following is an example of a MIME multi-part file that you can use to create your own.

    MIME-Version: 1.0
Content-Type: multipart/mixed; boundary="==MYBOUNDARY=="

--==MYBOUNDARY==
Content-Type: text/x-shellscript; charset="us-ascii"

#!/bin/bash
echo "Running custom user data script"

--==MYBOUNDARY==--
Amazon Linux 2023 user data

Amazon Linux 2023 (AL2023) introduces a new node initialization process nodeadm that uses a YAML configuration schema. If you're using self-managed node groups or an AMI with a launch template, you'll now need to provide additional cluster metadata explicitly when creating a new node group. An example of the minimum required parameters is as follows, where apiServerEndpoint, certificateAuthority, and service cidr are now required:

---
apiVersion: node.eks.aws/v1alpha1
kind: NodeConfig
spec:
  cluster:
    name: my-cluster
    apiServerEndpoint: https://example.com
    certificateAuthority: Y2VydGlmaWNhdGVBdXRob3JpdHk=
    cidr: 10.100.0.0/16

You'll typically set this configuration in your user data, either as-is or embedded within a MIME multi-part document:

MIME-Version: 1.0 
Content-Type: multipart/mixed; boundary="BOUNDARY"

--BOUNDARY
Content-Type: application/node.eks.aws

---
apiVersion: node.eks.aws/v1alpha1
kind: NodeConfig spec: [...]

--BOUNDARY--

In AL2, the metadata from these parameters was discovered from the Amazon EKS DescribeCluster API call. With AL2023, this behavior has changed since the additional API call risks throttling during large node scale ups. This change doesn't affect you if you're using managed node groups without a launch template or if you're using Karpenter. For more information on certificateAuthority and service cidr, see DescribeCluster in the Amazon EKS API Reference.

Bottlerocket user data

Bottlerocket structures user data in the TOML format. You can provide user data to be merged with the user data provided by Amazon EKS. For example, you can provide additional kubelet settings.

[settings.kubernetes.system-reserved]
cpu = "10m"
memory = "100Mi"
ephemeral-storage= "1Gi"

For more information about the supported settings, see Bottlerocket documentation. You can configure node labels and taints in your user data. However, we recommend that you configure these within your node group instead. Amazon EKS applies these configurations when you do so.

When user data is merged, formatting isn't preserved, but the content remains the same. The configuration that you provide in your user data overrides any settings that are configured by Amazon EKS. So, if you set settings.kubernetes.max-pods or settings.kubernetes.cluster-dns-ip, these values in your user data are applied to the nodes.

Amazon EKS doesn't support all valid TOML. The following is a list of known unsupported formats:

  • Quotes within quoted keys: 'quoted "value"' = "value"

  • Escaped quotes in values: str = "I'm a string. \"You can quote me\""

  • Mixed floats and integers: numbers = [ 0.1, 0.2, 0.5, 1, 2, 5 ]

  • Mixed types in arrays: contributors = ["foo@example.com", { name = "Baz", email = "baz@example.com" }]

  • Bracketed headers with quoted keys: [foo."bar.baz"]

Windows user data

Windows user data uses PowerShell commands. When creating a managed node group, your custom user data combines with Amazon EKS managed user data. Your PowerShell commands come first, followed by the managed user data commands, all within one <powershell></powershell> tag.

Note

When no AMI ID is specified in the launch template, don't use the Windows Amazon EKS Bootstrap script in user data to configure Amazon EKS.

Example user data is as follows.

<powershell>
Write-Host "Running custom user data script"
</powershell>

Specifying an AMI

If you have either of the following requirements, then specify an AMI ID in the ImageId field of your launch template. Select the requirement you have for additional information.

Bootstrapping is a term used to describe adding commands that can be run when an instance starts. For example, bootstrapping allows using extra kubelet arguments. You can pass arguments to the bootstrap.sh script by using eksctl without specifying a launch template. Or you can do so by specifying the information in the user data section of a launch template.

eksctl without specifying a launch template

Create a file named my-nodegroup.yaml with the following contents. Replace every example value with your own values. The --apiserver-endpoint, --b64-cluster-ca, and --dns-cluster-ip arguments are optional. However, defining them allows the bootstrap.sh script to avoid making a describeCluster call. This is useful in private cluster setups or clusters where you're scaling in and out nodes frequently. For more information on the bootstrap.sh script, see the bootstrap.sh file on GitHub.

  • The only required argument is the cluster name (my-cluster).

  • To retrieve an optimized AMI ID for ami-1234567890abcdef0, you can use the tables in the following sections:

  • To retrieve the certificate-authority for your cluster, run the following command.

    aws eks describe-cluster --query "cluster.certificateAuthority.data" --output text --name my-cluster --region region-code

  • To retrieve the api-server-endpoint for your cluster, run the following command.

    aws eks describe-cluster --query "cluster.endpoint" --output text --name my-cluster --region region-code

  • The value for --dns-cluster-ip is your service CIDR with .10 at the end. To retrieve the service-cidr for your cluster, run the following command. For example, if the returned value for is ipv4 10.100.0.0/16, then your value is 10.100.0.10.

    aws eks describe-cluster --query "cluster.kubernetesNetworkConfig.serviceIpv4Cidr" --output text --name my-cluster --region region-code

  • This example provides a kubelet argument to set a custom max-pods value using the bootstrap.sh script included with the Amazon EKS optimized AMI. The node group name can't be longer than 63 characters. It must start with letter or digit, but can also include hyphens and underscores for the remaining characters. For help with selecting my-max-pods-value, see Amazon EKS recommended maximum Pods for each Amazon EC2 instance type.

---
apiVersion: eksctl.io/v1alpha5
kind: ClusterConfig

metadata:
  name: my-cluster
  region: region-code

managedNodeGroups:
  - name: my-nodegroup
    ami: ami-1234567890abcdef0
    instanceType: m5.large
    privateNetworking: true
    disableIMDSv1: true
    labels: { x86-al2-specified-mng }
    overrideBootstrapCommand: |
      #!/bin/bash
      /etc/eks/bootstrap.sh my-cluster \
        --b64-cluster-ca certificate-authority \
        --apiserver-endpoint api-server-endpoint \
        --dns-cluster-ip service-cidr.10 \
        --kubelet-extra-args '--max-pods=my-max-pods-value' \
        --use-max-pods false

For every available eksctl config file option, see Config file schema in the eksctl documentation. The eksctl utility still creates a launch template for you and populates its user data with the data that you provide in the config file.

Create a node group with the following command.

eksctl create nodegroup --config-file=my-nodegroup.yaml
User data in a launch template

Specify the following information in the user data section of your launch template. Replace every example value with your own values. The --apiserver-endpoint, --b64-cluster-ca, and --dns-cluster-ip arguments are optional. However, defining them allows the bootstrap.sh script to avoid making a describeCluster call. This is useful in private cluster setups or clusters where you're scaling in and out nodes frequently. For more information on the bootstrap.sh script, see the bootstrap.sh file on GitHub.

  • The only required argument is the cluster name (my-cluster).

  • To retrieve the certificate-authority for your cluster, run the following command.

    aws eks describe-cluster --query "cluster.certificateAuthority.data" --output text --name my-cluster --region region-code

  • To retrieve the api-server-endpoint for your cluster, run the following command.

    aws eks describe-cluster --query "cluster.endpoint" --output text --name my-cluster --region region-code

  • The value for --dns-cluster-ip is your service CIDR with .10 at the end. To retrieve the service-cidr for your cluster, run the following command. For example, if the returned value for is ipv4 10.100.0.0/16, then your value is 10.100.0.10.

    aws eks describe-cluster --query "cluster.kubernetesNetworkConfig.serviceIpv4Cidr" --output text --name my-cluster --region region-code

  • This example provides a kubelet argument to set a custom max-pods value using the bootstrap.sh script included with the Amazon EKS optimized AMI. For help with selecting my-max-pods-value, see Amazon EKS recommended maximum Pods for each Amazon EC2 instance type.

MIME-Version: 1.0
Content-Type: multipart/mixed; boundary="==MYBOUNDARY=="

--==MYBOUNDARY==
Content-Type: text/x-shellscript; charset="us-ascii"

#!/bin/bash
set -ex
/etc/eks/bootstrap.sh my-cluster \
  --b64-cluster-ca certificate-authority \
  --apiserver-endpoint api-server-endpoint \
  --dns-cluster-ip service-cidr.10 \
  --kubelet-extra-args '--max-pods=my-max-pods-value' \
  --use-max-pods false

--==MYBOUNDARY==--

Bootstrapping is a term used to describe adding commands that can be run when an instance starts. You can pass arguments to the Start-EKSBootstrap.ps1 script by using eksctl without specifying a launch template. Or you can do so by specifying the information in the user data section of a launch template.

If you want to specify a custom Windows AMI ID, keep in mind the following considerations:

  • You must use a launch template and give the required bootstrap commands in the user data section. To retrieve your desired Windows ID, you can use the table in Amazon EKS optimized Windows AMIs.

  • There are several limits and conditions. For example, you must add eks:kube-proxy-windows to your AWS IAM Authenticator configuration map. For more information, see Limits and conditions when specifying an AMI ID.

Specify the following information in the user data section of your launch template. Replace every example value with your own values. The -APIServerEndpoint, -Base64ClusterCA, and -DNSClusterIP arguments are optional. However, defining them allows the Start-EKSBootstrap.ps1 script to avoid making a describeCluster call.

  • The only required argument is the cluster name (my-cluster).

  • To retrieve the certificate-authority for your cluster, run the following command.

    aws eks describe-cluster --query "cluster.certificateAuthority.data" --output text --name my-cluster --region region-code

  • To retrieve the api-server-endpoint for your cluster, run the following command.

    aws eks describe-cluster --query "cluster.endpoint" --output text --name my-cluster --region region-code

  • The value for --dns-cluster-ip is your service CIDR with .10 at the end. To retrieve the service-cidr for your cluster, run the following command. For example, if the returned value for is ipv4 10.100.0.0/16, then your value is 10.100.0.10.

    aws eks describe-cluster --query "cluster.kubernetesNetworkConfig.serviceIpv4Cidr" --output text --name my-cluster --region region-code

  • For additional arguments, see Bootstrap script configuration parameters.

    Note

    If you're using custom service CIDR, then you need to specify it using the -ServiceCIDR parameter. Otherwise, the DNS resolution for Pods in the cluster will fail.

<powershell>
[string]$EKSBootstrapScriptFile = "$env:ProgramFiles\Amazon\EKS\Start-EKSBootstrap.ps1"
& $EKSBootstrapScriptFile -EKSClusterName my-cluster `
	 -Base64ClusterCA certificate-authority `
	 -APIServerEndpoint api-server-endpoint `
	 -DNSClusterIP service-cidr.10
</powershell>

For more information, see Amazon Machine Images (AMI) in the Amazon EC2 User Guide. The Amazon EKS AMI build specification contains resources and configuration scripts for building a custom Amazon EKS AMI based on Amazon Linux. For more information, see Amazon EKS AMI Build Specification on GitHub. To build custom AMIs installed with other operating systems, see Amazon EKS Sample Custom AMIs on GitHub.

Important

When specifying an AMI, Amazon EKS doesn't merge any user data. Rather, you're responsible for supplying the required bootstrap commands for nodes to join the cluster. If your nodes fail to join the cluster, the Amazon EKS CreateNodegroup and UpdateNodegroupVersion actions also fail.

Limits and conditions when specifying an AMI ID

The following are the limits and conditions involved with specifying an AMI ID with managed node groups:

  • You must create a new node group to switch between specifying an AMI ID in a launch template and not specifying an AMI ID.

  • You aren't notified in the console when a newer AMI version is available. To update your node group to a newer AMI version, you need to create a new version of your launch template with an updated AMI ID. Then, you need to update the node group with the new launch template version.

  • The following fields can't be set in the API if you specify an AMI ID:

    • amiType

    • releaseVersion

    • version

  • Any taints set in the API are applied asynchronously if you specify an AMI ID. To apply taints prior to a node joining the cluster, you must pass the taints to kubelet in your user data using the --register-with-taints command line flag. For more information, see kubelet in the Kubernetes documentation.

  • When specifying a custom AMI ID for Windows managed node groups, add eks:kube-proxy-windows to your AWS IAM Authenticator configuration map. This is required for DNS to function properly.

    1. Open the AWS IAM Authenticator configuration map for editing.

      kubectl edit -n kube-system cm aws-auth

    2. Add this entry to the groups list under each rolearn associated with Windows nodes. Your configuration map should look similar to aws-auth-cm-windows.yaml.

      - eks:kube-proxy-windows

    3. Save the file and exit your text editor.