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A tool to use AWS IAM credentials to authenticate to a Kubernetes cluster.The initial work on this tool was driven by Heptio. The project receives contributions from multiple community engineers and is currently maintained by Heptio and Amazon EKS OSS Engineers.

If you are an administrator running a Kubernetes cluster on AWS, you already need to manage AWS IAM credentials to provision and update the cluster.By using AWS IAM Authenticator for Kubernetes, you avoid having to manage a separate credential for Kubernetes access.AWS IAM also provides a number of nice properties such as an out of band audit trail (via CloudTrail) and 2FA/MFA enforcement.

If you are building a Kubernetes installer on AWS, AWS IAM Authenticator for Kubernetes can simplify your bootstrap process.You won't need to somehow smuggle your initial admin credential securely out of your newly installed cluster.Instead, you can create a dedicatedKubernetesAdmin role at cluster provisioning time and set up Authenticator to allow cluster administrator logins.

Assuming you have a cluster running in AWS and you want to add AWS IAM Authenticator for Kubernetes support, you need to:

1. Create an IAM role you'll use to identify users.
2. Run the Authenticator server as a DaemonSet.
3. Configure your API server to talk to Authenticator.
4. Set up kubectl to use Authenticator tokens.

First, you must create one or more IAM roles that will be mapped to users/groups inside your Kubernetes cluster.The easiest way to do this is to log into the AWS Console:

• Choose the "Role for cross-account access" / "Provide access between AWS accounts you own" option.
• Paste in your AWS account ID number (available in the top right in the console).
• Your role does not need any additional policies attached.

This will create an IAM role with no permissions that can be assumed by authorized users/roles in your account.Note the Amazon Resource Name (ARN) of your role, which you will need below.

You can also do this in a single step using the AWS CLI instead of the AWS Console:

# get your account IDACCOUNT_ID=$(aws sts get-caller-identity --output text --query'Account')# define a role trust policy that opens the role to users in your account (limited by IAM policy)POLICY=$(echo -n'{"Version":"2012-10-17","Statement":[{"Effect":"Allow","Principal":{"AWS":"arn:aws:iam::';echo -n"$ACCOUNT_ID";echo -n':root"},"Action":"sts:AssumeRole","Condition":{}}]}')# create a role named KubernetesAdmin (will print the new role's ARN)aws iam create-role \  --role-name KubernetesAdmin \  --description"Kubernetes administrator role (for AWS IAM Authenticator for Kubernetes)." \  --assume-role-policy-document"$POLICY" \  --output text \  --query'Role.Arn'

You can also skip this step and use:

• An existing role (such as a cross-account access role).
• An IAM user (seemapUsers below).
• An EC2 instance or a federated role (seemapRoles below).

The server is meant to run on each of your master nodes as a DaemonSet with host networking so it can expose a localhost port.

For a sample ConfigMap and DaemonSet configuration, seedeploy/example.yaml.

If you're building an automated installer, you can also pre-generate the certificate, key, and webhook kubeconfig files easily usingaws-iam-authenticator init.This command will generate files and place them in the configured output directories.

You can run this on each master node prior to starting the API server.You could also generate them before provisioning master nodes and install them in the appropriate host paths.

If you do not pre-generate files,aws-iam-authenticator server will generate them on demand.This works but requires that you restart your Kubernetes API server after installation.

The Kubernetes API integrates with AWS IAM Authenticator for Kubernetes using atoken authentication webhook.When you runaws-iam-authenticator server, it will generate a webhook configuration file and save it onto the host filesystem.You'll need to add a single additional flag to your API server configuration:

--authentication-token-webhook-config-file=/etc/kubernetes/aws-iam-authenticator/kubeconfig.yaml

On many clusters, the API server runs as a static pod.You can add the flag to/etc/kubernetes/manifests/kube-apiserver.yaml.Make sure the host directory/etc/kubernetes/aws-iam-authenticator/ is mounted into your API server pod.You may also need to restart the kubelet daemon on your master node to pick up the updated static pod definition:

systemctl restart kubelet.service

The default behavior of the server is to source mappings exclusively from themapUsers andmapRoles fields of its configuration file. SeeFullConfiguration Format below for details.

Using the--backend-mode flag, you can configure the server to sourcemappings from two additional backends: an EKS-style ConfigMap(--backend-mode=EKSConfigMap) orIAMIdentityMapping custom resources(--backend-mode=CRD). The default backend, the server configuration filethat's mounted by the server pod, corresponds to--backend-mode=MountedFile.

You can pass a comma-separated list of these backends to have the server searchthem in order. For example, with--backend-mode=EKSConfigMap,MountedFile, theserver will search the EKS-style ConfigMap for mappings then, if it doesn'tfind a mapping for the given IAM role/user, the server configuration file. If amapping for the same IAM role/user exists in multiple backends, the server willuse the mapping in the backend that occurs first in the comma-separated list.In this example, if a mapping is found in the EKS ConfigMap then it will beused whether or not a duplicate or conflicting mapping exists in the serverconfiguration file.

Note that when setting a single backend, the server willonly source fromthat one and ignore the others even if they exist. For example, with--backend-mode=CRD, the server willonly source fromIAMIdentityMappingsand ignore the mounted file and EKS ConfigMap.

This is the default backend of mappings and sufficient for most users. SeeFull Configuration Format below for details.

This backend models each IAM mapping as anIAMIdentityMappingKubernetesCustomResource.This approach enables you to maintain mappings in a Kubernetes-native way usingkubectl or the API. Plus, syntax errors (like misaligned YAML) can be moreeasily caught and won't affect all mappings.

To setup anIAMIdentityMapping CRD you'll first need toapply the CRDmanifest:

kubectl apply -f deploy/iamidentitymapping.yaml

With the CRDs deployed you can then create Custom Resources which model yourIAM Identities. See./deploy/example-iamidentitymapping.yaml:

---apiVersion: iamauthenticator.k8s.aws/v1alpha1kind: IAMIdentityMappingmetadata:  name: kubernetes-adminspec:  # Arn of the User or Role to be allowed to authenticate  arn: arn:aws:iam::XXXXXXXXXXXX:user/KubernetesAdmin  # Username that Kubernetes will see the user as, this is useful for setting  # up allowed specific permissions for different users  username: kubernetes-admin  # Groups to be attached to your users/roles. For example `system:masters` to  # create cluster admin, or `system:nodes`, `system:bootstrappers` for nodes to  # access the API server.  groups:  - system:masters

The EKS-stylekube-system/aws-auth ConfigMap serves as the backend. TheConfigMap is expected to be in exactly the same format as in EKS clusters:https://docs.aws.amazon.com/eks/latest/userguide/add-user-role.html. This isuseful if you're migrating from/to EKS and want to keep your mappings, or arerunning EKS in addition to some other AWS cluster(s) and want to have the samemappings in each.

A local file specified by cfg.dynamicfilepath can serve as the backend. The filecontent is expected to be in exactly the same format as the EKSConfigMap. Wheneverthis file content changes, authenticator will automatically reload it. Thisprovides more flexibility on managing the ARN mappings.

Checkhttps://github.com/kubernetes-sigs/aws-iam-authenticator/blob/master/hack/dev/authenticator_with_dynamicfile_mode.yamlabout how to configure the DynamicFile mode.

Runmake e2e RUNNER=kind to play with a kind cluster with DynamicFile mode enable.

The aws-iam-authenticator can support reserved prefix for k8s username. If the reserved prefix isset, then the username with the reserved prefix will not be authenticated with the error"username must not begin with with the following prefixes:".

Checkhttps://github.com/kubernetes-sigs/aws-iam-authenticator/blob/master/hack/dev/authenticator_with_dynamicfile_mode.yamlabout how to configure the reserved prefix.

This requires a 1.10+kubectl binary to work. If you receivePlease enter Username: when trying to usekubectl you need to update to the latestkubectl

Finally, once the server is set up you'll want to authenticate.You will still need akubeconfig that has the public data about your cluster (cluster CA certificate, endpoint address).Theusers section of your configuration, however, should include an exec section (refer to the v1.10 docs)::

# [...]users:-name:kubernetes-adminuser:exec:apiVersion:client.authentication.k8s.io/v1beta1command:aws-iam-authenticatorargs:        -"token"        -"-i"        -"REPLACE_ME_WITH_YOUR_CLUSTER_ID"        -"-r"        -"REPLACE_ME_WITH_YOUR_ROLE_ARN"# no client certificate/key needed here!

This means thekubeconfig is entirely public data and can be shared across all Authenticator users.It may make sense to upload it to a trusted public location such as AWS S3.

Make sure you have theaws-iam-authenticator binary installed.You can install it withgo install sigs.k8s.io/aws-iam-authenticator/cmd/aws-iam-authenticator@latest.

To authenticate, runkubectl --kubeconfig /path/to/kubeconfig" [...].kubectl willexec theaws-iam-authenticator binary with the supplied params in your kubeconfig which will generate a token and pass it to the apiserver.The token is valid for 15 minutes (the shortest value AWS permits) and can be reused multiple times.

You can also specify session name when generating the token by including--session-name or -s parameter. This parameter cannot be used along with--forward-session-name.

You can also omit-r ROLE_ARN to sign the token with your existing credentials without assuming a dedicated role.This is useful if you want to authenticate as an IAM user directly or if you want to authenticate using an EC2 instance role or a federated role.

Clusters managed byKops can be configured to use Authenticator. For usage instructions see theKops documentation.

It works using the AWSsts:GetCallerIdentity API endpoint.This endpoint returns information about whatever AWS IAM credentials you use to connect to it.

We use this API in a somewhat unusual way by having the Authenticator client generate and pre-sign a request to the endpoint.We serialize that request into a token that can pass through the Kubernetes authentication system.

The token is passed through the Kubernetes API server and into the Authenticator server's/authenticate endpoint via a webhook configuration.The Authenticator server validates all the parameters of the pre-signed request to make sure nothing looks funny.It then submits the request to the realhttps://sts.amazonaws.com server, which validates the client's HMAC signature and returns information about the user.Now that the server knows the AWS identity of the client, it translates this identity into a Kubernetes user and groups via a simple static mapping.

This mechanism is borrowed with a few changes fromVault.

The Authenticator cluster ID is a unique-per-cluster identifier that prevents certain replay attacks.Specifically, it prevents one Authenticator server (e.g., in a dev environment) from using a client's token to authenticate to another Authenticator server in another cluster.

The cluster ID does need to be unique per-cluster, but it doesn't need to be a secret.Some good choices are:

• A random ID such as fromopenssl rand 16 -hex
• The domain name of your Kubernetes API server

TheVault documentation also explains this attack (seeX-Vault-AWS-IAM-Server-ID).

Credentials can be specified for use withaws-iam-authenticator via any of the methods available to theAWS SDK for Go.This includes specifying AWS credentials with enviroment variables or by utilizing a credentials file.

AWSnamed profiles are supported byaws-iam-authenticatorvia theAWS_PROFILE environment variable. For example, to authenticate with credentials specified in thedev profile theAWS_PROFILE canbe exported or specified explictly (e.g.,AWS_PROFILE=dev kubectl get all). If noAWS_PROFILE is set, thedefault profile is used.

TheAWS_PROFILE can also be specified directly in the kubeconfig fileas part of theexec flow. For example, to specifythat credentials from thedev named profile should always be used byaws-iam-authenticator, your kubeconfig would include anenvkey thats sets the profile:

apiVersion:v1clusters:-cluster:server:${server}certificate-authority-data:${cert}name:kubernetescontexts:-context:cluster:kubernetesuser:awsname:awscurrent-context:awskind:Configpreferences:{}users:-name:awsuser:exec:apiVersion:client.authentication.k8s.io/v1beta1command:aws-iam-authenticatorenv:      -name:"AWS_PROFILE"value:"dev"args:        -"token"        -"-i"        -"mycluster"

This method allows the appropriate profile to be used implicitly. Note that any environment variables set as part of theexec flow willtake precedence over what's already set in your environment.

Federated AWS users often will have a "meaningful" attribute mapped onto their assumed role, such as an email address, through the account's AWS configuration.These assumed sessions havea few parts, therole idandcaller-specified-role-name. By default, when a federated user uses the--role option ofaws-iam-authenticator to assume a new role thecaller-specified-role-name will be converted to a random token and therole id carries through to the newly assumed role.

Usingaws-iam-authenticator token ... --forward-session-name will map the originalcaller-specified-role-name attribute onto the new STS assumed session.This can be helpful for quickly attempting to associate "who performed action X on the K8 cluster".

Please note,this should not be considered definitive and needs to be cross referenced via therole id (which remains consistent) with CloudTrail logsas a user could potentially change this on the client side.

It is possible to make requests to the Kubernetes API from a client that is outside the cluster, be that using thebare Kubernetes REST API or from one of the language specific Kubernetes clients(e.g.,Python). In order to do so, you must create a bearer token thatis included with the request to the API. This bearer token requires you append the stringk8s-aws-v1. with abase64 encoded string of a signed HTTP request to the STS GetCallerIdentity Query API. This is then sent it in theAuthorization header of the request. Something to note though is that the IAM Authenticator explicitly omitsbase64 padding to avoid any= characters thus guaranteeing a string safe to use in URLs. Below is an example inPython on how this token would be constructed:

importbase64importboto3importrefrombotocore.signersimportRequestSignerdefget_bearer_token(cluster_id,region):STS_TOKEN_EXPIRES_IN=60session=boto3.session.Session()client=session.client('sts',region_name=region)service_id=client.meta.service_model.service_idsigner=RequestSigner(service_id,region,'sts','v4',session.get_credentials(),session.events    )params= {'method':'GET','url':'https://sts.{}.amazonaws.com/?Action=GetCallerIdentity&Version=2011-06-15'.format(region),'body': {},'headers': {'x-k8s-aws-id':cluster_id        },'context': {}    }signed_url=signer.generate_presigned_url(params,region_name=region,expires_in=STS_TOKEN_EXPIRES_IN,operation_name=''    )base64_url=base64.urlsafe_b64encode(signed_url.encode('utf-8')).decode('utf-8')# remove any base64 encoding padding:return'k8s-aws-v1.'+re.sub(r'=*','',base64_url)# If making a HTTP request you would create the authorization headers as follows:headers= {'Authorization':'Bearer '+get_bearer_token('my_cluster','us-east-1')}

If your client fails with an error likecould not get token: AccessDenied [...], you can try assuming the role with the AWS CLI directly:

# AWS CLI version of `aws-iam-authenticator token -r arn:aws:iam::ACCOUNT:role/ROLE`:$ aws sts assume-role --role-arn arn:aws:iam::ACCOUNT:role/ROLE --role-session-nametest

If that fails, there are a few possible problems to check for:

• Make sure your base AWS credentials are available in your shell (aws sts get-caller-identity can help troubleshoot this).

• Make sure the target role allows your source account access (in the role trust policy).

• Make sure your source principal (user/role/group) has an IAM policy that allowssts:AssumeRole for the target role.

• Make sure you don't have any explicit deny policies attached to your user, group, or in AWS Organizations that would prevent thests:AssumeRole.

• Try simulating thests:AssumeRole call in thePolicy Simulator.

The client and server have the same configuration format.They can share the same exact configuration file, since there are no secrets stored in the configuration.

# a unique-per-cluster identifier to prevent replay attacks (see above)clusterID:my-dev-cluster.example.com# default IAM role to assume for `aws-iam-authenticator token`defaultRole:arn:aws:iam::000000000000:role/KubernetesAdmin# server listener configurationserver:# localhost port where the server will serve the /authenticate endpointport:21362# (default)# state directory for generated TLS certificate and private keysstateDir:/var/aws-iam-authenticator# (default)# output `path` where a generated webhook kubeconfig will be stored.generateKubeconfig:/etc/kubernetes/aws-iam-authenticator.kubeconfig# (default)# role to assume before querying EC2 API in order to discover metadata like EC2 private DNS Nameec2DescribeInstancesRoleARN:arn:aws:iam::000000000000:role/DescribeInstancesRole# AWS Account IDs to scrub from server logs. (Defaults to empty list)scrubbedAccounts:  -"111122223333"  -"222233334444"# each mapRoles entry maps an IAM role to a username and set of groups# Each username and group can optionally contain template parameters:#  1) "{{AccountID}}" is the 12 digit AWS ID.#  2) "{{SessionName}}" is the role session name, with `@` characters#     transliterated to `-` characters.#  3) "{{SessionNameRaw}}" is the role session name, without character#     transliteration (available in version >= 0.5).mapRoles:# statically map arn:aws:iam::000000000000:role/KubernetesAdmin to cluster admin  -rolearn:arn:aws:iam::000000000000:role/KubernetesAdminusername:kubernetes-admingroups:    -system:masters# map EC2 instances in my "KubernetesNode" role to users like# "aws:000000000000:instance:i-0123456789abcdef0". Only use this if you# trust that the role can only be assumed by EC2 instances. If an IAM user# can assume this role directly (with sts:AssumeRole) they can control# SessionName.  -rolearn:arn:aws:iam::000000000000:role/KubernetesNodeusername:aws:{{AccountID}}:instance:{{SessionName}}groups:    -system:bootstrappers    -aws:instances# map nodes that should conform to the username "system:node:<private-DNS>".  This# requires the authenticator to query the EC2 API in order to discover the private# DNS of the EC2 instance originating the authentication request.  Optionally, you# may specify a role that should be assumed before querying the EC2 API with the# key "server.ec2DescribeInstancesRoleARN" (see above).  -rolearn:arn:aws:iam::000000000000:role/KubernetesNodeusername:system:node:{{EC2PrivateDNSName}}groups:    -system:nodes    -system:bootstrappers# map federated users in my "KubernetesAdmin" role to users like# "admin:alice-example.com". The SessionName is an arbitrary role name# like an e-mail address passed by the identity provider. Note that if this# role is assumed directly by an IAM User (not via federation), the user# can control the SessionName.  -rolearn:arn:aws:iam::000000000000:role/KubernetesAdminusername:admin:{{SessionName}}groups:    -system:masters# map federated users in my "KubernetesOtherAdmin" role to users like# "alice-example.com". The SessionName is an arbitrary role name# like an e-mail address passed by the identity provider. Note that if this# role is assumed directly by an IAM User (not via federation), the user# can control the SessionName.  Note that the "{{SessionName}}" macro is# quoted to ensure it is properly parsed as a string.  -rolearn:arn:aws:iam::000000000000:role/KubernetesOtherAdminusername:"{{SessionName}}"groups:    -system:masters# If unalterable identification of an IAM User is desirable, you can map against# AccessKeyID.  -rolearn:arn:aws:iam::000000000000:role/KubernetesOtherAdminusername:"admin:{{AccessKeyID}}"groups:    -system:masters# each mapUsers entry maps an IAM user to a static username and set of groupsmapUsers:# map user IAM user Alice in 000000000000 to user "alice" in group "system:masters"  -userarn:arn:aws:iam::000000000000:user/Aliceusername:alicegroups:    -system:masters# automatically map IAM ARN from these accounts to username.# NOTE: Always use quotes to avoid the account numbers being recognized as numbers# instead of strings by the yaml parser.mapAccounts:  -"012345678901"  -"456789012345"# source mappings from this file (mapUsers, mapRoles, & mapAccounts)backendMode:  -MountedFile

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