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Auditing and logging

Collecting and analyzing [audit] logs is useful for a variety of different reasons. Logs can help with root cause analysis and attribution, i.e. ascribing a change to a particular user. When enough logs have been collected, they can be used to detect anomalous behaviors too. On EKS, the audit logs are sent to Amazon Cloudwatch Logs. The audit policy for EKS is as follows:

apiVersion: audit.k8s.io/v1beta1
kind: Policy
rules:
  # Log full request and response for changes to aws-auth ConfigMap in kube-system namespace
  - level: RequestResponse
    namespaces: ["kube-system"]
    verbs: ["update", "patch", "delete"]
    resources:
      - group: "" # core
        resources: ["configmaps"]
        resourceNames: ["aws-auth"]
    omitStages:
      - "RequestReceived"
  # Do not log watch operations performed by kube-proxy on endpoints and services
  - level: None
    users: ["system:kube-proxy"]
    verbs: ["watch"]
    resources:
      - group: "" # core
        resources: ["endpoints", "services", "services/status"]
  # Do not log get operations performed by kubelet on nodes and their statuses
  - level: None
    users: ["kubelet"] # legacy kubelet identity
    verbs: ["get"]
    resources:
      - group: "" # core
        resources: ["nodes", "nodes/status"]
  # Do not log get operations performed by the system:nodes group on nodes and their statuses
  - level: None
    userGroups: ["system:nodes"]
    verbs: ["get"]
    resources:
      - group: "" # core
        resources: ["nodes", "nodes/status"]
  # Do not log get and update operations performed by controller manager, scheduler, and endpoint-controller on endpoints in kube-system namespace
  - level: None
    users:
      - system:kube-controller-manager
      - system:kube-scheduler
      - system:serviceaccount:kube-system:endpoint-controller
    verbs: ["get", "update"]
    namespaces: ["kube-system"]
    resources:
      - group: "" # core
        resources: ["endpoints"]
  # Do not log get operations performed by apiserver on namespaces and their statuses/finalizations
  - level: None
    users: ["system:apiserver"]
    verbs: ["get"]
    resources:
      - group: "" # core
        resources: ["namespaces", "namespaces/status", "namespaces/finalize"]
  # Do not log get and list operations performed by controller manager on metrics.k8s.io resources
  - level: None
    users:
      - system:kube-controller-manager
    verbs: ["get", "list"]
    resources:
      - group: "metrics.k8s.io"
  # Do not log access to health, version, and swagger non-resource URLs
  - level: None
    nonResourceURLs:
      - /healthz*
      - /version
      - /swagger*
  # Do not log events resources
  - level: None
    resources:
      - group: "" # core
        resources: ["events"]
  # Log request for updates/patches to nodes and pods statuses by kubelet and node problem detector
  - level: Request
    users: ["kubelet", "system:node-problem-detector", "system:serviceaccount:kube-system:node-problem-detector"]
    verbs: ["update", "patch"]
    resources:
      - group: "" # core
        resources: ["nodes/status", "pods/status"]
    omitStages:
      - "RequestReceived"
  # Log request for updates/patches to nodes and pods statuses by system:nodes group
  - level: Request
    userGroups: ["system:nodes"]
    verbs: ["update", "patch"]
    resources:
      - group: "" # core
        resources: ["nodes/status", "pods/status"]
    omitStages:
      - "RequestReceived"
  # Log delete collection requests by namespace-controller in kube-system namespace
  - level: Request
    users: ["system:serviceaccount:kube-system:namespace-controller"]
    verbs: ["deletecollection"]
    omitStages:
      - "RequestReceived"
  # Log metadata for secrets, configmaps, and tokenreviews to protect sensitive data
  - level: Metadata
    resources:
      - group: "" # core
        resources: ["secrets", "configmaps"]
      - group: authentication.k8s.io
        resources: ["tokenreviews"]
    omitStages:
      - "RequestReceived"
  # Log requests for serviceaccounts/token resources
  - level: Request
    resources:
      - group: "" # core
        resources: ["serviceaccounts/token"]
  # Log get, list, and watch requests for various resource groups
  - level: Request
    verbs: ["get", "list", "watch"]
    resources: 
      - group: "" # core
      - group: "admissionregistration.k8s.io"
      - group: "apiextensions.k8s.io"
      - group: "apiregistration.k8s.io"
      - group: "apps"
      - group: "authentication.k8s.io"
      - group: "authorization.k8s.io"
      - group: "autoscaling"
      - group: "batch"
      - group: "certificates.k8s.io"
      - group: "extensions"
      - group: "metrics.k8s.io"
      - group: "networking.k8s.io"
      - group: "policy"
      - group: "rbac.authorization.k8s.io"
      - group: "scheduling.k8s.io"
      - group: "settings.k8s.io"
      - group: "storage.k8s.io"
    omitStages:
      - "RequestReceived"
  # Default logging level for known APIs to log request and response
  - level: RequestResponse
    resources: 
      - group: "" # core
      - group: "admissionregistration.k8s.io"
      - group: "apiextensions.k8s.io"
      - group: "apiregistration.k8s.io"
      - group: "apps"
      - group: "authentication.k8s.io"
      - group: "authorization.k8s.io"
      - group: "autoscaling"
      - group: "batch"
      - group: "certificates.k8s.io"
      - group: "extensions"
      - group: "metrics.k8s.io"
      - group: "networking.k8s.io"
      - group: "policy"
      - group: "rbac.authorization.k8s.io"
      - group: "scheduling.k8s.io"
      - group: "settings.k8s.io"
      - group: "storage.k8s.io"
    omitStages:
      - "RequestReceived"
  # Default logging level for all other requests to log metadata only
  - level: Metadata
    omitStages:
      - "RequestReceived"

Recommendations

Enable audit logs

The audit logs are part of the EKS managed Kubernetes control plane logs that are managed by EKS. Instructions for enabling/disabling the control plane logs, which includes the logs for the Kubernetes API server, the controller manager, and the scheduler, along with the audit log, can be found here, https://docs.aws.amazon.com/eks/latest/userguide/control-plane-logs.html#enabling-control-plane-log-export.

Info

When you enable control plane logging, you will incur costs for storing the logs in CloudWatch. This raises a broader issue about the ongoing cost of security. Ultimately you will have to weigh those costs against the cost of a security breach, e.g. financial loss, damage to your reputation, etc. You may find that you can adequately secure your environment by implementing only some of the recommendations in this guide.

Warning

The maximum size for a CloudWatch Logs entry is 256KB whereas the maximum Kubernetes API request size is 1.5MiB. Log entries greater than 256KB will either be truncated or only include the request metadata.

Utilize audit metadata

Kubernetes audit logs include two annotations that indicate whether or not a request was authorized authorization.k8s.io/decision and the reason for the decision authorization.k8s.io/reason. Use these attributes to ascertain why a particular API call was allowed.

Create alarms for suspicious events

Create an alarm to automatically alert you where there is an increase in 403 Forbidden and 401 Unauthorized responses, and then use attributes like host, sourceIPs, and k8s_user.username to find out where those requests are coming from.

Analyze logs with Log Insights

Use CloudWatch Log Insights to monitor changes to RBAC objects, e.g. Roles, RoleBindings, ClusterRoles, and ClusterRoleBindings. A few sample queries appear below:

Lists updates to the aws-auth ConfigMap:

fields @timestamp, @message
| filter @logStream like "kube-apiserver-audit"
| filter verb in ["update", "patch"]
| filter objectRef.resource = "configmaps" and objectRef.name = "aws-auth" and objectRef.namespace = "kube-system"
| sort @timestamp desc

Lists creation of new or changes to validation webhooks:

fields @timestamp, @message
| filter @logStream like "kube-apiserver-audit"
| filter verb in ["create", "update", "patch"] and responseStatus.code = 201
| filter objectRef.resource = "validatingwebhookconfigurations"
| sort @timestamp desc

Lists create, update, delete operations to Roles:

fields @timestamp, @message
| sort @timestamp desc
| limit 100
| filter objectRef.resource="roles" and verb in ["create", "update", "patch", "delete"]

Lists create, update, delete operations to RoleBindings:

fields @timestamp, @message
| sort @timestamp desc
| limit 100
| filter objectRef.resource="rolebindings" and verb in ["create", "update", "patch", "delete"]

Lists create, update, delete operations to ClusterRoles:

fields @timestamp, @message
| sort @timestamp desc
| limit 100
| filter objectRef.resource="clusterroles" and verb in ["create", "update", "patch", "delete"]

Lists create, update, delete operations to ClusterRoleBindings:

fields @timestamp, @message
| sort @timestamp desc
| limit 100
| filter objectRef.resource="clusterrolebindings" and verb in ["create", "update", "patch", "delete"]

Plots unauthorized read operations against Secrets:

fields @timestamp, @message
| sort @timestamp desc
| limit 100
| filter objectRef.resource="secrets" and verb in ["get", "watch", "list"] and responseStatus.code="401"
| stats count() by bin(1m)

List of failed anonymous requests:

fields @timestamp, @message, sourceIPs.0
| sort @timestamp desc
| limit 100
| filter user.username="system:anonymous" and responseStatus.code in ["401", "403"]

Audit your CloudTrail logs

AWS APIs called by pods that are utilizing IAM Roles for Service Accounts (IRSA) are automatically logged to CloudTrail along with the name of the service account. If the name of a service account that wasn't explicitly authorized to call an API appears in the log, it may be an indication that the IAM role's trust policy was misconfigured. Generally speaking, Cloudtrail is a great way to ascribe AWS API calls to specific IAM principals.

Use CloudTrail Insights to unearth suspicious activity

CloudTrail insights automatically analyzes write management events from CloudTrail trails and alerts you of unusual activity. This can help you identify when there's an increase in call volume on write APIs in your AWS account, including from pods that use IRSA to assume an IAM role. See Announcing CloudTrail Insights: Identify and Response to Unusual API Activity for further information.

Additional resources

As the volume of logs increases, parsing and filtering them with Log Insights or another log analysis tool may become ineffective. As an alternative, you might want to consider running Sysdig Falco and ekscloudwatch. Falco analyzes audit logs and flags anomalies or abuse over an extended period of time. The ekscloudwatch project forwards audit log events from CloudWatch to Falco for analysis. Falco provides a set of default audit rules along with the ability to add your own.

Yet another option might be to store the audit logs in S3 and use the SageMaker Random Cut Forest algorithm to anomalous behaviors that warrant further investigation.

Tools and resources

The following commercial and open source projects can be used to assess your cluster's alignment with established best practices: