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aws-eks-asg-rolling-update-handler

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This application handles rolling upgrades for AWS ASGs for EKS by replacing outdated nodes by new nodes. Outdated nodes are defined as nodes whose current configuration does not match its ASG's current launch template version or launch configuration.

Inspired by aws-asg-roller, this application only has one purpose: Scale down outdated nodes gracefully.

Unlike aws-asg-roller, it will not attempt to control the amount of nodes at all; it will scale up enough new nodes to move the pods from the old nodes to the new nodes, and then evict the old nodes.

It will not adjust the desired size back to its initial desired size like aws-asg-roller does, it will simply leave everything else up to cluster-autoscaler.

Note that unlike other solutions, this application actually uses the resources to determine how many instances should be spun up before draining the old nodes. This is much better, because simply using the initial number of instances is completely useless in the event that the ASG's update on the launch configuration/template is a change of instance type.

Behavior

On interval, this application:

  1. Iterates over each ASG discovered by the CLUSTER_NAME, AUTODISCOVERY_TAGS environment variables or the ones defined in the AUTO_SCALING_GROUP_NAMES environment variable, in that order.
  2. Iterates over each instance of each ASG
  3. Checks if there's any instance with an outdated launch template version
  4. If ASG uses MixedInstancesPolicy, checks if there's any instances with an instance type that isn't part of the list of instance type overrides
  5. Checks if there's any instance with an outdated launch configuration
  6. If any of the conditions defined in the step 3, 4 or 5 are met for any instance, begin the rolling update process for that instance

The steps of each action are persisted directly on the old nodes via annotations (i.e. when the old node starts rolling out, gets drained, and gets scheduled for termination). Therefore, this application will not run into any issues if it is restarted, rescheduled or stopped at any point in time.

NOTE: Ensure that your PodDisruptionBudgets - if you have any - are properly configured. This usually means having at least 1 allowed disruption at all time (i.e. at least minAvailable: 1 with at least 2 replicas OR maxUnavailable: 1)

Usage

Environment variable Description Required Default
CLUSTER_NAME Name of the eks-cluster, used in place of AUTODISCOVERRY_TAGS and AUTO_SCALING_GROUP_NAMES. Checks for k8s.io/cluster-autoscaler/<CLUSTER_NAME>: owned and k8s.io/cluster-autoscaler/enabled: true tags on ASG yes ""
AUTODISCOVERY_TAGS Comma separated key value string with tags to autodiscover ASGs, used in place of CLUSTER_NAME and AUTO_SCALING_GROUP_NAMES. yes ""
AUTO_SCALING_GROUP_NAMES Comma-separated list of ASGs, CLUSTER_NAME takes priority. yes ""
IGNORE_DAEMON_SETS Whether to ignore DaemonSets when draining the nodes no true
DELETE_EMPTY_DIR_DATA Whether to delete empty dir data when draining the nodes no true
AWS_REGION Self-explanatory no us-west-2
ENVIRONMENT If set to dev, will try to create the Kubernetes client using your local kubeconfig. Any other values will use the in-cluster configuration no ""
EXECUTION_INTERVAL Duration to sleep between each execution in seconds no 20
EXECUTION_TIMEOUT Maximum execution duration before timing out in seconds no 900
POD_TERMINATION_GRACE_PERIOD How long to wait for a pod to terminate in seconds; 0 means "delete immediately"; set to a negative value to use the pod's terminationGracePeriodSeconds. no -1
METRICS_PORT Port to bind metrics server to no 8080
METRICS Expose metrics in Prometheus format at :${METRICS_PORT}/metrics no ""
SLOW_MODE If enabled, every time a node is terminated during an execution, the current execution will stop rather than continuing to the next ASG no false
EAGER_CORDONING If enabled, all outdated nodes will get cordoned before any rolling update action. The default mode is to cordon a node just before draining it. See #41 for possible consequences of enabling this. no false
EXCLUDE_FROM_EXTERNAL_LOAD_BALANCERS If enabled, node label node.kubernetes.io/exclude-from-external-load-balancers=true will be added to nodes before draining. See #131 for more information no false

NOTE: Only one of CLUSTER_NAME, AUTODISCOVERY_TAGS or AUTO_SCALING_GROUP_NAMES must be set.

Metrics

Metric name Metric type Labels Description
rolling_update_handler_node_groups Gauge Node groups managed by the handler
rolling_update_handler_outdated_nodes Gauge node_group The number of outdated nodes
rolling_update_handler_updated_nodes Gauge node_group The number of updated nodes
rolling_update_handler_scaled_up_nodes Counter node_group The total number of nodes scaled up
rolling_update_handler_scaled_down_nodes Counter node_group The total number of nodes scaled down
rolling_update_handler_drained_nodes_total Counter node_group The total number of drained nodes
rolling_update_handler_errors Counter The total number of errors

Permissions

To function properly, this application requires the following permissions on AWS:

  • autoscaling:DescribeAutoScalingGroups
  • autoscaling:DescribeAutoScalingInstances
  • autoscaling:DescribeLaunchConfigurations
  • autoscaling:SetDesiredCapacity
  • autoscaling:TerminateInstanceInAutoScalingGroup
  • autoscaling:UpdateAutoScalingGroup
  • ec2:DescribeLaunchTemplates
  • ec2:DescribeInstances

Deploying on Kubernetes

apiVersion: v1
kind: ServiceAccount
metadata:
  name: aws-eks-asg-rolling-update-handler
  namespace: kube-system
  labels:
    app: aws-eks-asg-rolling-update-handler
---
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  name: aws-eks-asg-rolling-update-handler
  labels:
    app: aws-eks-asg-rolling-update-handler
rules:
  - apiGroups:
      - "*"
    resources:
      - "*"
    verbs:
      - get
      - list
      - watch
  - apiGroups:
      - "*"
    resources:
      - nodes
    verbs:
      - get
      - list
      - watch
      - update
      - patch
  - apiGroups:
      - "*"
    resources:
      - pods/eviction
    verbs:
      - get
      - list
      - create
  - apiGroups:
      - "*"
    resources:
      - pods
    verbs:
      - get
      - list
---
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRoleBinding
metadata:
  name: aws-eks-asg-rolling-update-handler
  labels:
    app: aws-eks-asg-rolling-update-handler
roleRef:
  kind: ClusterRole
  name: aws-eks-asg-rolling-update-handler
  apiGroup: rbac.authorization.k8s.io
subjects:
  - kind: ServiceAccount
    name: aws-eks-asg-rolling-update-handler
    namespace: kube-system
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: aws-eks-asg-rolling-update-handler
  namespace: kube-system
  labels:
    app: aws-eks-asg-rolling-update-handler
spec:
  replicas: 1
  selector:
    matchLabels:
      app: aws-eks-asg-rolling-update-handler
  template:
    metadata:
      labels:
        app: aws-eks-asg-rolling-update-handler
    spec:
      automountServiceAccountToken: true
      serviceAccountName: aws-eks-asg-rolling-update-handler
      restartPolicy: Always
      dnsPolicy: Default
      containers:
        - name: aws-eks-asg-rolling-update-handler
          image: twinproduction/aws-eks-asg-rolling-update-handler
          imagePullPolicy: Always
          env:
            - name: AUTO_SCALING_GROUP_NAMES
              value: "asg-1,asg-2,asg-3" # REPLACE THESE VALUES FOR THE NAMES OF THE ASGs

Deploying with Helm

For the chart associated to this project, see TwiN/helm-charts:

helm repo add twin https://twin.github.io/helm-charts
helm repo update
helm install aws-eks-asg-rolling-update-handler twin/aws-eks-asg-rolling-update-handler

Developing

To run the application locally, make sure your local kubeconfig file is configured properly (i.e. you can use kubectl).

Once you've done that, set the local environment variable ENVIRONMENT to dev and AUTO_SCALING_GROUP_NAMES to a comma-separated list of auto scaling group names.

Your local aws credentials must also be valid (i.e. you can use awscli)

Special thanks

I had originally worked on deitch/aws-asg-roller, but due to the numerous conflicts it had with cluster-autoscaler, I decided to make a project that heavily relies on cluster-autoscaler rather than simply coexist with it, with a much bigger emphasis on maintaining high availability during rolling upgrades.

In any case, this project was inspired by aws-asg-roller and the code for comparing launch template versions also comes from there, hence why this special thanks section exists.