Kops: Upgrading to CoreDNS does not remove kube-dns deployments

[syscll]

1. What kops version are you running? The command kops version, will display
this information.

Version 1.11.0 (git-2c2042465)

2. What Kubernetes version are you running? kubectl version will print the
version if a cluster is running or provide the Kubernetes version specified as
a kops flag.

1.11.6

3. What cloud provider are you using?

4. What commands did you run? What is the simplest way to reproduce this issue?

kops edit cluster

Add CoreDNS provider:

kubeDNS:
  provider: CoreDNS

Update cluster:

kops update cluster --yes

Rolling update:

kops rolling-update cluster --yes

5. What happened after the commands executed?

Everything ran successfully. However, I still see kube-dns deployments:

$ kubectl get deployments -n=kube-system
NAME                   DESIRED   CURRENT   UP-TO-DATE   AVAILABLE   AGE
coredns                2         2         2            2           1d
dns-controller         1         1         1            1           1y
kube-dns               2         2         2            2           1y
kube-dns-autoscaler    1         1         1            1           1y
...

6. What did you expect to happen?

I expected kube-dns to be replaced by CoreDNS.

7. Please provide your cluster manifest. Execute
kops get --name my.example.com -o yaml to display your cluster manifest.
You may want to remove your cluster name and other sensitive information.

apiVersion: kops/v1alpha2
kind: Cluster
metadata:
  creationTimestamp: 2017-12-19T15:09:49Z
  name: [REDACTED]
spec:
  additionalPolicies:
    node: |
      [{"Effect": "Allow","Action": ["route53:ChangeResourceRecordSets"],"Resource": ["arn:aws:route53:::hostedzone/*"]},{"Effect": "Allow","Action": ["route53:ListHostedZones","route53:ListResourceRecordSets"],"Resource": ["*"]}]
  api:
    loadBalancer:
      type: Public
  authorization:
    rbac: {}
  channel: stable
  cloudProvider: aws
  configBase: [REDACTED]
  docker:
    version: 18.06.1
  etcdClusters:
  - etcdMembers:
    - instanceGroup: master-eu-central-1b
      name: b
    name: main
  - etcdMembers:
    - instanceGroup: master-eu-central-1b
      name: b
    name: events
  iam:
    allowContainerRegistry: true
    legacy: false
  kubeAPIServer:
    oidcClientID: [REDACTED]
    oidcIssuerURL: https://accounts.google.com
    oidcUsernameClaim: email
  kubeDNS:
    provider: CoreDNS
  kubelet:
    anonymousAuth: false
  kubernetesApiAccess:
  - [REDACTED]
  kubernetesVersion: 1.11.6
  masterInternalName: [REDACTED]
  masterPublicName: [REDACTED]
  networkCIDR: [REDACTED]
  networking:
    weave:
      mtu: 8912
  nonMasqueradeCIDR: [REDACTED]
  sshAccess:
  - [REDACTED]
  subnets:
  - cidr: [REDACTED]
    name: eu-central-1b
    type: Private
    zone: eu-central-1b
  - cidr: [REDACTED]
    name: utility-eu-central-1b
    type: Utility
    zone: eu-central-1b
  - cidr: [REDACTED]
    name: public-eu-central-1b
    type: Public
    zone: eu-central-1b
  topology:
    bastion:
      bastionPublicName: [REDACTED]
    dns:
      type: Public
    masters: private
    nodes: private

8. Please run the commands with most verbose logging by adding the -v 10 flag.
Paste the logs into this report, or in a gist and provide the gist link here.

9. Anything else do we need to know?

Am I correct in thinking the kube-dns deployments should have been deleted?
Is it safe to manually delete the deployments?

[joshbranham]

From what I can gather, you can remove the deployments. The kube-dns service used by the cluster has the label selector k8s-app: kube-dns, which lines up with the label on the CoreDNS pods, so technically you are running both at the same time which is fine. If you are migrating and testing, you could just scale the kube-dns and kube-dns-autoscaler deployments to 0 till you are ready to delete.

With that said, I am unsure if it's within the scope of this project to delete that deployment after switching to CoreDNS. My guess is not, but curious what other people think.

[syscll]

I can confirm that DNS still seems to be working as expected after scaling down kube-dns and kube-dns-autoscaler.

I am also unsure if it's within the scope of this project to delete the deployments, so I'll leave this open for now and see what others think.

[joshbranham]

I see two options to make this easier:

1. Update the documentation for switching to CoreDNS to state the above findings
2. Update kops to output a note to the user upon switching the kubeDNS field

I think 1 is better, rather than having lots of printing for various conditions in the code.

[integrii]

I agree with @joshphp - the upgrade process for coredns is largely undocumented. This is fine for just deploying a cluster, but people running production systems would appreciate more information on how coredns is upgraded.

It sounds like this is as simple as adding something to the docs that says:

If you are upgrading to coredns, kube-dns will be left in place and must be removed manually.

[jmthvt]

I read everywhere that we should scale kube-dns-autoscaler to 0 or remove it - however that implies that coredns can't autoscale? Shouldn't we configure the dns-autoscaler to scale coredns instead?

[cristian-marin-hs]

@jeyglk yes, you can configure the kube-dns-autoscaler to link to the coredns deployment. You just need to edit the autoscaler container command to use --target=Deployment/coredns instead of --target=Deployment/kube-dns

[syscll]

The coredns/deployment repo also has a good document on scaling: https://github.com/coredns/deployment/blob/master/kubernetes/Scaling_CoreDNS.md

[leoskyrocker]

Shouldn't we configure the dns-autoscaler to scale coredns instead?

@jeyglk After editing our kops cluster to use CoreDNS, I observed that it already created an autoscaler deployment called "coredns-autoscaler", in addition to the pre-existing kube-dns-autoscaler. It seems that there's no need to modify the existing autoscaler rather than just removing it.