I have two EKS cluster running on control plane version 1.18 with 10 managed worker node group, waiting on third party vendors to provide support for some application running on these clusters. Wanted to know what sort of outages will occur when AWS automatically updates the control plane version to 1.19. Will any outage occur or will the worker nodes keep working besides being on an older version. Just do not want to be surprised with an outage when the automatic update occurs.
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I'm experiencing downtimes whenever the GKE cluster gets upgraded during the maintenance window. My services (APIs) become unreachable for like ~5min.
The cluster Location type is set to "Zonal", and all my pods have 2 replicas. The only affected pods seem to be the ones using nginx ingress controller.
Is there anything I can do to prevent this? I read that using Regional clusters should prevent downtimes in the control plane, but I'm not sure if it's related to my case. Any hints would be appreciated!
You mention "downtime" but is this downtime for you using the control plane (i.e. kubectl stop working) or is it downtime in that the end user who is using the services stops seeing the service working.
A GKE upgrade upgrades two parts of the cluster: the control plane or master nodes, and the worker nodes. These are two separate upgrades although they can happen at the same time depending on your configuration of the cluster.
Regional clusters can help with that, but they will cost more as you are having more nodes, but the upside is that the cluster is more resilient.
Going back to the earlier point about the control plane vs node upgrades. The control plane upgrade does NOT affect the end-user/customer perspective. The services will remaining running.
The node upgrade WILL affect the customer so you should consider various techniques to ensure high availability and resiliency on your services.
A common technique is to increase replicas and also to include pod antiaffinity. This will ensure the pods are scheduled on different nodes, so when the node upgrade comes around, it doesn't take the entire service out because the cluster scheduled all the replicas on the same node.
You mention the nginx ingress controller in your question. If you are using Helm to install that into your cluster, then out of the box, it is not setup to use anti-affinity, so it is liable to be taken out of service if all of its replicas get scheduled onto the same node, and then that node gets marked for upgrade or similar.
I've been trying to figure out what happens when the Kubernetes master fails in a cluster that only has one master. Do web requests still get routed to pods if this happens, or does the entire system just shut down?
According to the OpenShift 3 documentation, which is built on top of Kubernetes, (https://docs.openshift.com/enterprise/3.2/architecture/infrastructure_components/kubernetes_infrastructure.html), if a master fails, nodes continue to function properly, but the system looses its ability to manage pods. Is this the same for vanilla Kubernetes?
In typical setups, the master nodes run both the API and etcd and are either largely or fully responsible for managing the underlying cloud infrastructure. When they are offline or degraded, the API will be offline or degraded.
In the event that they, etcd, or the API are fully offline, the cluster ceases to be a cluster and is instead a bunch of ad-hoc nodes for this period. The cluster will not be able to respond to node failures, create new resources, move pods to new nodes, etc. Until both:
Enough etcd instances are back online to form a quorum and make progress (for a visual explanation of how this works and what these terms mean, see this page).
At least one API server can service requests
In a partially degraded state, the API server may be able to respond to requests that only read data.
However, in any case, life for applications will continue as normal unless nodes are rebooted, or there is a dramatic failure of some sort during this time, because TCP/ UDP services, load balancers, DNS, the dashboard, etc. Should all continue to function for at least some time. Eventually, these things will all fail on different timescales. In single master setups or complete API failure, DNS failure will probably happen first as caches expire (on the order of minutes, though the exact timing is configurable, see the coredns cache plugin documentation). This is a good reason to consider a multi-master setup–DNS and service routing can continue to function indefinitely in a degraded state, even if etcd can no longer make progress.
There are actions that you could take as an operator which would accelerate failures, especially in a fully degraded state. For instance, rebooting a node would cause DNS queries and in fact probably all pod and service networking functionality until at least one master comes back online. Restarting DNS pods or kube-proxy would also be bad.
If you'd like to test this out yourself, I recommend kubeadm-dind-cluster, kind or, for more exotic setups, kubeadm on VMs or bare metal. Note: kubectl proxy will not work during API failure, as that routes traffic through the master(s).
Kubernetes cluster without a master is like a company running without a Manager.
No one else can instruct the workers(k8s components) other than the Manager(master node)(even you, the owner of the cluster, can only instruct the Manager)
Everything works as usual. Until the work is finished or something stopped them.(because the master node died after assigning the works)
As there is no Manager to re-assign any work for them, the workers will wait and wait until the Manager comes back.
The best practice is to assign multiple managers(master) to your cluster.
Although your data plane and running applications does not immediately starts breaking but there are several scenarios where cluster admins will wish they had multi-master setup. Key to understanding the impact would be understanding which all components talk to master for what and how and more importantly when will they fail if master fails.
Although your application pods running on data plane will not get immediately impacted but imagine a very possible scenario - your traffic suddenly surged and your horizontal pod autoscaler kicked in. The autoscaling would not work as Metrics Server collects resource metrics from Kubelets and exposes them in Kubernetes apiserver through Metrics API for use by Horizontal Pod Autoscaler and vertical pod autoscaler ( but your API server is already dead).If your pod memory shoots up because of high load then it will eventually lead to getting killed by k8s OOM killer. If any of the pods die, then since controller manager and scheduler talks to API Server to watch for current state of pods so they too will fail. In short a new pod will not be scheduled and your application may stop responding.
One thing to highlight is that Kubernetes system components communicate only with the API server. They don’t
talk to each other directly and so their functionality themselves could fail I guess. Unavailable master plane can mean several things - failure of any or all of these components - API server,etcd, kube scheduler, controller manager or worst the entire node had crashed.
If API server is unavailable - no one can use kubectl as generally all commands talk to API server ( meaning you cannot connect to cluster, cannot login into any pods to check anything on container file system. You will not be able to see application logs unless you have any additional centralized log management system).
If etcd database failed or got corrupted - your entire cluster state data is gone and the admins would want to restore it from backups as early as possible.
In short - a failed single master control plane although may not immediately impact traffic serving capability but cannot be relied on for serving your traffic.
The kubernetes master in one of my GKE clusters became unresponsive last night following the infrastructure issue in us-central1-a.
Whenever I run "kubectl get pods" in the default namespace I get the following error message:
Error from server: an error on the server has prevented the request from succeeding
If I run "kubectl get pods --namespace=kube-system", I only see the kube-proxy and the fluentd-logging daemon.
I have trying scaling the cluster down to 0 and then scaling it back up. I have also tried downgrading and upgrading the cluster but that seems to apply only to the nodes (not the master). Is there any GKE/K8S API command to issue a restart to the kubernetes master?
There is not a command that will allow you to restart the Kubernetes master in GKE (since the master is considered a part of the managed service). There is automated infrastructure (and then an oncall engineer from Google) that is responsible for restarting the master if it is unhealthy.
In this particular cases, restarting the master had no effect on restoring it to normal behavior because Google Compute Engine Incident #16011 caused an outage on 2016-06-28 for GKE masters running in us-central1-a (even though that isn't indicated on the Google Cloud Status Dashboard). During the incident, many masters were unavailable.
If you had tried to create a GCE cluster using kube-up.sh during that time, you would have similarly seen that it would be unable to create a functional master VM due to the SSD Persistent disk latency issues.
I'm trying to have at least one version to upgrade ready, if you trying to upgrade the master, it will restart and work within few minutes. Otherwise you should wait around 3 days while Google team will reboot it. On e-mail/phone, then won't help you. And unless you have payed support (transition to which taking few days), they won't give a bird.
I need to deploy a web application in gke. The application consists of two pods and needs to scale to ~30 replicas.
Rolling updates take ~30s/pod in our setup.
Old title: How do I enable the deployments API on GKE cluster?
I tried to use deployments as they allow to update multiple pods in parallel.
But, as nshttpd pointed out in #google-containers on the kubernetes slack:
I may be wrong, but GKE clusters don’t have beta features I thought. so if you want Deployments you’ll have to spin up your own cluster.
GKE clusters actually do have beta features. But Deployments were an alpha feature in the 1.1 release (which is the current supported release) and are graduating to beta for the upcoming 1.2 release. Once they are a beta feature, you will be able to use them in GKE.
The rolling update command is really just syntactic sugar around first creating a new replication controller, scaling it up by one, scaling the existing replication controller down by one, and repeating until the old replication controller has size zero. You can do this yourself at a much faster rate if going one pod at a time is too slow. You may also want to file a feature request on github to add a flag to the rolling update command to update multiple pods in parallel.
In GKE every cluster has a single master endpoint, which is managed by Google Container Engine. Is this master node high available?
I deploy a beautiful cluster of redundant nodes with kubernetes but what happen if the master node goes down? How can i test this situation?
In Google Container Engine the master is managed for you and kept running by Google. According to the SLA for Google Container Engine the master should be available at least 99.5% of the time.
In addition to what Robert Bailey said about GKE keeping the master available for you, it's worth noting that Kubernetes / GKE clusters are designed (and tested) to continue operating properly in the presence of failures. If the master is unavailable, you temporarily lose the ability change what's running in the cluster (i.e. schedule new work or modify existing resources), but everything that's already running will continue working properly.