Instance Groups

kops has the concept of “instance groups”, which are a group of similar machines. On AWS, they map toan AutoScalingGroup.

By default, a cluster has:

  • An instance group called nodes spanning all the zones; these instances are your workers.
  • One instance group for each master zone, called master-<zone> (e.g. master-us-east-1c). These normally haveminimum size and maximum size = 1, so they will run a single instance. We do this so that the cloud willalways relaunch masters, even if everything is terminated at once. We have an instance group per zonebecause we need to force the cloud to run an instance in every zone, so we can mount the master volumes - wecannot do that across zones.

Instance Groups Disclaimer

  • When there is only one availability zone in a region (eu-central-1) and you would like to run multiple masters,you have to define multiple instance groups for each of those masters. (e.g. master-eu-central-1-a andmaster-eu-central-1-b and so on…)
  • If instance groups are not defined correctly (particularly when there are an even number of master or multiplegroups of masters into one availability zone in a single region), etcd servers will not start and master nodes will not check in. This is because etcd servers are configured per availability zone. DNS and Route53 would be the first places to check when these problems are happening.

Listing instance groups

kops get instancegroups

  1. NAME                    ROLE    MACHINETYPE     MIN     MAX     ZONES
  2. master-us-east-1c       Master                  1       1       us-east-1c
  3. nodes                   Node    t2.medium       2       2

You can also use the kops get ig alias.

Change the instance type in an instance group

First you edit the instance group spec, using kops edit ig nodes. Change the machine type to t2.large,for example. Now if you kops get ig, you will see the large instance size. Note though that these changeshave not yet been applied (this may change soon though!).

To preview the change:

kops update cluster <clustername>

  1. ...
  2. Will modify resources:
  3.   *awstasks.LaunchConfiguration launchConfiguration/mycluster.mydomain.com
  4.     InstanceType t2.medium -> t2.large

Presuming you’re happy with the change, go ahead and apply it: kops update cluster <clustername> --yes

This change will apply to new instances only; if you’d like to roll it out immediately to all the instancesyou have to perform a rolling update.

See a preview with: kops rolling-update cluster

Then restart the machines with: kops rolling-update cluster --yes

This will drain nodes, restart them with the new instance type, and validate them after startup.

Resize an instance group

The procedure to resize an instance group works the same way:

  • Edit the instance group, set minSize and maxSize to the desired size: kops edit ig nodes
  • Preview changes: kops update cluster <clustername>
  • Apply changes: kops update cluster <clustername> --yes
  • (you do not need a rolling-update when changing instancegroup sizes)

Changing the root volume size or type

The default volume size for Masters is 64 GB, while the default volume size for a node is 128 GB.

The procedure to resize the root volume works the same way:

  • Edit the instance group, set rootVolumeSize and/or rootVolumeType to the desired values: kops edit ig nodes
  • rootVolumeType must be one of supported volume types, e.g. gp2 (default), io1 (high performance) or standard (for testing).
  • If rootVolumeType is set to io1 then you can define the number of Iops by specifying rootVolumeIops (defaults to 100 if not defined)
  • Preview changes: kops update cluster <clustername>
  • Apply changes: kops update cluster <clustername> --yes
  • Rolling update to update existing instances: kops rolling-update cluster --yes

For example, to set up a 200GB gp2 root volume, your InstanceGroup spec might look like:

  1. metadata:
  2.   creationTimestamp: "2016-07-11T04:14:00Z"
  3.   name: nodes
  4. spec:
  5.   machineType: t2.medium
  6.   maxSize: 2
  7.   minSize: 2
  8.   role: Node
  9.   rootVolumeSize: 200
  10.   rootVolumeType: gp2

For example, to set up a 200GB io1 root volume with 200 provisioned Iops, your InstanceGroup spec might look like:

  1. metadata:
  2.   creationTimestamp: "2016-07-11T04:14:00Z"
  3.   name: nodes
  4. spec:
  5.   machineType: t2.medium
  6.   maxSize: 2
  7.   minSize: 2
  8.   role: Node
  9.   rootVolumeSize: 200
  10.   rootVolumeType: io1
  11.   rootVolumeIops: 200

Creating a new instance group

Suppose you want to add a new group of nodes, perhaps with a different instance type. You do this using kops create ig <InstanceGroupName> --subnet <zone(s)>. Currently the--subnet flag is required, and it receives the zone(s) of the subnet(s) in which the instance group will be. The command opens an editor with a skeleton configuration, allowing you to edit it before creation.

So the procedure is:

  • kops create ig morenodes --subnet us-east-1a

    or, in case you need it to be in more than one subnet, use a comma-separated list:

  • kops create ig morenodes --subnet us-east-1a,us-east-1b,us-east-1c

  • Preview: kops update cluster <clustername>
  • Apply: kops update cluster <clustername> --yes
  • (no instances need to be relaunched, so no rolling-update is needed)

Moving from one instance group spanning multiple AZs to one instance group per AZ

It may be beneficial to have one IG per AZ rather than one IG spanning multiple AZs. One common example is, when you have a persistent volume claim bound to an AWS EBS Volume this volume is bound to the AZ it has been created in so any resource (e.g. a StatefulSet) depending on that volume is bound to that same AZ. In this case you have to ensure that there is at least one node running in that same AZ, which is not guaranteed by one IG. This however can be guaranteed by one IG per AZ.

So the procedure is:

  • kops edit ig nodes
  • Remove two of the subnets, e.g. eu-central-1b and eu-central-1c
    • Alternatively you can also delete the existing IG and create a new one with a more suitable name
  • kops create ig nodes-eu-central-1b --subnet eu-central-1b
  • kops create ig nodes-eu-central-1c --subnet eu-central-1c
  • Preview: kops update cluster <clustername>
  • Apply: kops update cluster <clustername> --yes
  • Rolling update to update existing instances: kops rolling-update cluster --yes

Converting an instance group to use spot instances

Follow the normal procedure for reconfiguring an InstanceGroup, but set the maxPrice property to your bid.For example, “0.10” represents a spot-price bid of $0.10 (10 cents) per hour.

An example spec looks like this:

  1. metadata:
  2.   creationTimestamp: "2016-07-10T15:47:14Z"
  3.   name: nodes
  4. spec:
  5.   machineType: t2.medium
  6.   maxPrice: "0.01"
  7.   maxSize: 3
  8.   minSize: 3
  9.   role: Node

So the procedure is:

  • Edit: kops edit ig nodes
  • Preview: kops update cluster <clustername>
  • Apply: kops update cluster <clustername> --yes
  • Rolling-update, only if you want to apply changes immediately: kops rolling-update cluster

Adding Taints or Labels to an Instance Group

If you’re running Kubernetes 1.6.0 or later, you can also control taints in the InstanceGroup.The taints property takes a list of strings. The following example would add two taints to an IG,using the same edit -> update -> rolling-update process as above.

Additionally, nodeLabels can be added to an IG in order to take advantage of Pod Affinity. Every node in the IG will be assigned the desired labels. For more information see the labels documentation.

  1. metadata:
  2.   creationTimestamp: "2016-07-10T15:47:14Z"
  3.   name: nodes
  4. spec:
  5.   machineType: m3.medium
  6.   maxSize: 3
  7.   minSize: 3
  8.   role: Node
  9.   taints:
  10.   - dedicated=gpu:NoSchedule
  11.   - team=search:PreferNoSchedule
  12.   nodeLabels:
  13.     spot: "false"

Resizing the master

(This procedure should be pretty familiar by now!)

Your master instance group will probably be called master-us-west-1c or something similar.

kops edit ig master-us-west-1c

Add or set the machineType:

  1. spec:
  2.   machineType: m3.large

  • Preview changes: kops update cluster <clustername>

  • Apply changes: kops update cluster <clustername> --yes

  • Rolling-update, only if you want to apply changes immediately: kops rolling-update cluster

If you want to minimize downtime, scale the master ASG up to size 2, then wait for that new master tobe Ready in kubectl get nodes, then delete the old master instance, and scale the ASG back down to size 1. (Afuture version of rolling-update will probably do this automatically)

Deleting an instance group

If you decide you don’t need an InstanceGroup any more, you delete it using: kops delete ig <name>

Example: kops delete ig morenodes

No kops update cluster nor kops rolling-update is needed, so be careful when deleting an instance group, your nodes will be deleted automatically (and note this is not currently graceful, so there may be interruptions to workloads where the pods are running on those nodes).

EBS Volume Optimization

EBS-Optimized instances can be created by setting the following field:

  1. spec:
  2.   rootVolumeOptimization: true

Additional user-data for cloud-init

Kops utilizes cloud-init to initialize and setup a host at boot time. However in certain cases you may already be leveraging certain features of cloud-init in your infrastructure and would like to continue doing so. More information on cloud-init can be found here

Additional user-data can be passed to the host provisioning by setting the additionalUserData field. A list of valid user-data content-types can be found here

Example:

  1. spec:
  2.   additionalUserData:
  3.   - name: myscript.sh
  4.     type: text/x-shellscript
  5.     content: |
  6.       #!/bin/sh
  7.       echo "Hello World.  The time is now $(date -R)!" | tee /root/output.txt
  8.   - name: local_repo.txt
  9.     type: text/cloud-config
  10.     content: |
  11.       #cloud-config
  12.       apt:
  13.         primary:
  14.           - arches: [default]
  15.             uri: http://local-mirror.mydomain
  16.             search:
  17.               - http://local-mirror.mydomain
  18.               - http://archive.ubuntu.com

Add Tags on AWS autoscalling groups and instances

If you need to add tags on auto scaling groups or instances (propagate ASG tags), you can add it in the instance group specs with cloudLabels. Cloud Labels defined at the cluster spec level will also be inherited.

  1. # Example for nodes
  2. apiVersion: kops/v1alpha2
  3. kind: InstanceGroup
  4. metadata:
  5.   labels:
  6.     kops.k8s.io/cluster: k8s.dev.local
  7.   name: nodes
  8. spec:
  9.   cloudLabels:
  10.     billing: infra
  11.     environment: dev
  12.   associatePublicIp: false
  13.   machineType: m4.xlarge
  14.   maxSize: 20
  15.   minSize: 2
  16.   role: Node

Suspending Scaling Processes on AWS Autoscaling groups

Autoscaling groups automatically include multiple scaling processesthat keep our ASGs healthy. In some cases, you may want to disable certain scaling activities.

An example of this is if you are running multiple AZs in an ASG while using a Kubernetes Autoscaler.The autoscaler will remove specific instances that are not being used. In some cases, the AZRebalance processwill rescale the ASG without warning.

  1. # Example for nodes
  2. apiVersion: kops/v1alpha2
  3. kind: InstanceGroup
  4. metadata:
  5.   labels:
  6.     kops.k8s.io/cluster: k8s.dev.local
  7.   name: nodes
  8. spec:
  9.   machineType: m4.xlarge
  10.   maxSize: 20
  11.   minSize: 2
  12.   role: Node
  13.   suspendProcesses:
  14.   - AZRebalance

Attaching existing Load Balancers to Instance Groups

Instance groups can be linked to up to 10 load balancers. When attached, any instance launched willautomatically register itself to the load balancer. For example, if you can create an instance groupdedicated to running an ingress controller exposed on aNodePort, you canmanually create a load balancer and link it to the instance group. Traffic to the load balancer will nowautomatically go to one of the nodes.

You can specify either loadBalancerName to link the instance group to an AWS Classic ELB or you canspecify targetGroupARN to link the instance group to a target group, which are used by Applicationload balancers and Network load balancers.

  1. # Example ingress nodes
  2. apiVersion: kops/v1alpha2
  3. kind: InstanceGroup
  4. metadata:
  5.   labels:
  6.     kops.k8s.io/cluster: k8s.dev.local
  7.   name: ingress
  8. spec:
  9.   machineType: m4.large
  10.   maxSize: 2
  11.   minSize: 2
  12.   role: Node
  13.   externalLoadBalancers:
  14.   - targetGroupARN: arn:aws:elasticloadbalancing:eu-west-1:123456789012:targetgroup/my-ingress-target-group/0123456789abcdef
  15.   - loadBalancerName: my-elb-classic-load-balancer

Enabling Detailed-Monitoring on AWS instances

Detailed-Monitoring will cause the monitoring data to be available every 1 minute instead of every 5 minutes. Enabling Detailed Monitoring. In production environments you may want to consider to enable detailed monitoring for quicker troubleshooting.

Note: that enabling detailed monitoring is a subject for charge

  1. # Example for nodes
  2. apiVersion: kops/v1alpha2
  3. kind: InstanceGroup
  4. metadata:
  5.   labels:
  6.     kops.k8s.io/cluster: k8s.dev.local
  7.   name: nodes
  8. spec:
  9.   detailedInstanceMonitoring: true
  10.   machineType: t2.medium
  11.   maxSize: 2
  12.   minSize: 2
  13.   role: Node