kubelet 1.17: `MaxPods` field not recognized in config

[etungsten]

Image I'm using:
aws-k8s-1.17 v0.4.1

What I expected to happen:
kubelet to recognize the MaxPods field in the config

What actually happened:
kubelet failed to decode the MaxPods field.

How to reproduce the problem:
Launch instance, with mostly default settings, journalctl -u kubelet shows the following:

bash-5.0# journalctl -u kubelet                                                                                                                                 
-- Logs begin at Mon 2020-07-13 18:40:33 UTC, end at Mon 2020-07-13 18:42:18 UTC. --
Jul 13 18:41:07 ip-192-168-1-151.us-west-2.compute.internal systemd[1]: Starting Kubelet...
Jul 13 18:41:07 ip-192-168-1-151.us-west-2.compute.internal host-ctr[3153]: time="2020-07-13T18:41:07Z" level=info msg="Pulling with Amazon ECR Resolver" ref="ec
r.aws/arn:aws:ecr:us-west-2:602401143452:repository/eks/pause-amd64:3.1"
Jul 13 18:41:07 ip-192-168-1-151.us-west-2.compute.internal host-ctr[3153]: time="2020-07-13T18:41:07Z" level=info msg="Pulled successfully" img="ecr.aws/arn:aws
:ecr:us-west-2:602401143452:repository/eks/pause-amd64:3.1"
Jul 13 18:41:07 ip-192-168-1-151.us-west-2.compute.internal host-ctr[3153]: time="2020-07-13T18:41:07Z" level=info msg=Unpacking... img="ecr.aws/arn:aws:ecr:us-w
est-2:602401143452:repository/eks/pause-amd64:3.1"
Jul 13 18:41:07 ip-192-168-1-151.us-west-2.compute.internal host-ctr[3153]: time="2020-07-13T18:41:07Z" level=info msg="Tagging image" imageName="602401143452.dk
r.ecr.us-west-2.amazonaws.com/eks/pause-amd64:3.1"
Jul 13 18:41:07 ip-192-168-1-151.us-west-2.compute.internal host-ctr[3153]: time="2020-07-13T18:41:07Z" level=info msg="Not starting host container, pull-image-o
nly mode specified"
Jul 13 18:41:08 ip-192-168-1-151.us-west-2.compute.internal kubelet[3203]: Flag --containerd has been deprecated, This is a cadvisor flag that was mistakenly reg
istered with the Kubelet. Due to legacy concerns, it will follow the standard CLI deprecation timeline before being removed.
Jul 13 18:41:08 ip-192-168-1-151.us-west-2.compute.internal kubelet[3203]: W0713 18:41:08.799142    3203 server.go:191] Warning: For remote container runtime, --
pod-infra-container-image is ignored in kubelet, which should be set in that remote runtime instead
Jul 13 18:41:08 ip-192-168-1-151.us-west-2.compute.internal kubelet[3203]: W0713 18:41:08.804669    3203 codec.go:127] using lenient decoding as strict decoding 
failed: strict decoder error for ---
Jul 13 18:41:08 ip-192-168-1-151.us-west-2.compute.internal kubelet[3203]: kind: KubeletConfiguration
Jul 13 18:41:08 ip-192-168-1-151.us-west-2.compute.internal kubelet[3203]: apiVersion: kubelet.config.k8s.io/v1beta1
Jul 13 18:41:08 ip-192-168-1-151.us-west-2.compute.internal kubelet[3203]: address: 0.0.0.0
Jul 13 18:41:08 ip-192-168-1-151.us-west-2.compute.internal kubelet[3203]: authentication:
Jul 13 18:41:08 ip-192-168-1-151.us-west-2.compute.internal kubelet[3203]:   anonymous:
Jul 13 18:41:08 ip-192-168-1-151.us-west-2.compute.internal kubelet[3203]:     enabled: false
Jul 13 18:41:08 ip-192-168-1-151.us-west-2.compute.internal kubelet[3203]:   webhook:
Jul 13 18:41:08 ip-192-168-1-151.us-west-2.compute.internal kubelet[3203]:     cacheTTL: 2m0s
Jul 13 18:41:08 ip-192-168-1-151.us-west-2.compute.internal kubelet[3203]:     enabled: true
Jul 13 18:41:08 ip-192-168-1-151.us-west-2.compute.internal kubelet[3203]:   x509:
Jul 13 18:41:08 ip-192-168-1-151.us-west-2.compute.internal kubelet[3203]:     clientCAFile: "/etc/kubernetes/pki/ca.crt"
Jul 13 18:41:08 ip-192-168-1-151.us-west-2.compute.internal kubelet[3203]: authorization:
Jul 13 18:41:08 ip-192-168-1-151.us-west-2.compute.internal kubelet[3203]:   mode: Webhook
Jul 13 18:41:08 ip-192-168-1-151.us-west-2.compute.internal kubelet[3203]:   webhook:
Jul 13 18:41:08 ip-192-168-1-151.us-west-2.compute.internal kubelet[3203]:     cacheAuthorizedTTL: 5m0s
Jul 13 18:41:08 ip-192-168-1-151.us-west-2.compute.internal kubelet[3203]:     cacheUnauthorizedTTL: 30s
Jul 13 18:41:08 ip-192-168-1-151.us-west-2.compute.internal kubelet[3203]: clusterDomain: cluster.local
Jul 13 18:41:08 ip-192-168-1-151.us-west-2.compute.internal kubelet[3203]: clusterDNS:
Jul 13 18:41:08 ip-192-168-1-151.us-west-2.compute.internal kubelet[3203]: - 10.100.0.10
Jul 13 18:41:08 ip-192-168-1-151.us-west-2.compute.internal kubelet[3203]: resolvConf: "/etc/resolv.conf"
Jul 13 18:41:08 ip-192-168-1-151.us-west-2.compute.internal kubelet[3203]: hairpinMode: hairpin-veth
Jul 13 18:41:08 ip-192-168-1-151.us-west-2.compute.internal kubelet[3203]: cgroupDriver: systemd
Jul 13 18:41:08 ip-192-168-1-151.us-west-2.compute.internal kubelet[3203]: cgroupRoot: "/"
Jul 13 18:41:08 ip-192-168-1-151.us-west-2.compute.internal kubelet[3203]: runtimeRequestTimeout: 15m
Jul 13 18:41:08 ip-192-168-1-151.us-west-2.compute.internal kubelet[3203]: featureGates:
Jul 13 18:41:08 ip-192-168-1-151.us-west-2.compute.internal kubelet[3203]:   RotateKubeletServerCertificate: true
Jul 13 18:41:08 ip-192-168-1-151.us-west-2.compute.internal kubelet[3203]:   CSIMigration: false
Jul 13 18:41:08 ip-192-168-1-151.us-west-2.compute.internal kubelet[3203]: serializeImagePulls: false
Jul 13 18:41:08 ip-192-168-1-151.us-west-2.compute.internal kubelet[3203]: serverTLSBootstrap: true
Jul 13 18:41:08 ip-192-168-1-151.us-west-2.compute.internal kubelet[3203]: configMapAndSecretChangeDetectionStrategy: Cache
Jul 13 18:41:08 ip-192-168-1-151.us-west-2.compute.internal kubelet[3203]: tlsCipherSuites:
Jul 13 18:41:08 ip-192-168-1-151.us-west-2.compute.internal kubelet[3203]: - TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256
Jul 13 18:41:08 ip-192-168-1-151.us-west-2.compute.internal kubelet[3203]: MaxPods: 29
Jul 13 18:41:08 ip-192-168-1-151.us-west-2.compute.internal kubelet[3203]: : v1beta1.KubeletConfiguration.Authentication: v1beta1.KubeletAuthentication.TypeMeta:
 APIVersion: Address: ReadObject: found unknown field: MaxPods, error found in #10 byte of ...|{"MaxPods":29,"addre|..., bigger context ...|{"MaxPods":29,"addres
s":"0.0.0.0","apiVersion":"kubelet.conf|...

[etungsten]

kubelet successfully decodes this field in other Kubernetes variants. So far it's only the 1.17 variant that has this issue. There's no indication of this field being deprecated in 1.17. The field is still listed:
https://github.com/kubernetes/kubernetes/blob/d1c2f63bd4fc89d80e9bb6d21b5c1c24d241ad25/staging/src/k8s.io/kubelet/config/v1beta1/types.go#L462-L470

[bcressey]

Should it be maxPods instead of MaxPods?

[etungsten]

Should it be maxPods instead of MaxPods?

Ah you're right! I guess strict decoding was recently enabled in 1.17 and this field was only decoded in previous kubelet version because of the lenient decoding?