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Kubernetes

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Revision as of 16:01, 11 May 2021 by imported>Legoktm (→‎Add a new service: deploy ns/users to all clusters)
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For information about Kubernetes in the Toolforge environment see Help:Toolforge/Kubernetes.

Kubernetes (often abbreviated k8s) is an open-source system for automating deployment, and management of applications running in containers. This page collects some notes/docs on the Kubernetes setup in the Foundation production environment.

Clusters

The list of currently maintained clusters in WMF, split by realm and team is at Kubernetes/Clusters

Packages

We deploy kubernetes in WMF production using Debian packages where appropriate. There is an upgrade policy in place for defining the timeframe and versions we run at every point in time. It's under Kubernetes/Kubernetes_Infrastructure_upgrade_policy. For more technical information on how we build the Debian packages have a look at Kubernetes/Packages

Images

For how our images are built and maintained have a look at Kubernetes/Images

Services

A service in Kubernetes is an 'abstract way to expose an application running on a set of workloads as a network service'.

Debugging

For a quick intro into the debugging actions one can take during a problem in production look at Kubernetes/Helm. There will also be a guide posted under Kubernetes/Kubectl

Administration

Create a new cluster

Documentation for creating a new cluster is in Kubernetes/Clusters/New

Add a new service

To add a new service to the clusters:

  • Ensure the service has it's ports registered at: Service ports
  • Create deployment user/tokens in the puppet private (you can use a random generated password, no strict guideline for it) and public repos.
  • Add a Kubernetes namespace:
  • At this point, you can safely merge the change (after somebody from Service Ops validates it of course). Please do it though when you have time to run the following command, to avoid impacting other people rolling out changes later on.
  • The first thing to do is to work in staging, updating the admin config.
    • On deploy1002: sudo -icd /srv/deployment-charts/helmfile.d/admin_ng/; kube_env admin staging-codfw; helmfile -e staging-codfw -i apply
    • The command above should show you a change in namespaces/quotas/etc.. related to your new service. If this is not the case (for example, you also see other changes) ping somebody from the Service Ops team! There might be some work waiting to be applied. It will also log to IRC for you.
    • You can then run kubectl get ns which should now show your new namespace. And kubectl get pods -n $YOUR-SERVICE-NAME should show a tiller pod.
    • Repeat for the staging-eqiad and the prod clusters. Even if you aren't ready to fully deploy your service, you don't want to leave undeployed things pending for the next person to run into.
  • Then you can proceed to deploy the new service to staging for real. Don't worry for TLS (if needed) since in staging it will be added a default config for your service auto-magically. Different thing is Production, but there is a step later on about it :D
    • On deploy1002: cd /srv/deployment-charts/helmfile.d/services/YOUR-SERVICE-NAME-HERE; helmfile -e staging -i apply
    • The magic command above will show a diff related to the new service, make sure that everything looks fine and then hit Yes to proceed.
    • You should now be able to test your new service in staging! You can use the handy endpoint http(s)://staging.svc.eqiad.wmnet:$YOUR-SERVICE-PORT to quickly test if everything works as expected.
  • Now you can move to Production!
  • Create certificates for the new service, if it has an HTTPS endpoint (remember that this step for staging is automatically handled for you, but for production it is not).
  • If the new service requires specific secrets, commit them to /srv/private/hieradata/role/common/deployment_server.yaml
  • At this point, you need to update the admin config for eqiad and codfw (if you have configs for both of course):
    • On deploy1002: sudo -i; cd /srv/deployment-charts/helmfile.d/admin/codfw/; kube_env admin codfw; ./cluster-helmfile.sh -i apply
    • On deploy1002: sudo -i; cd /srv/deployment-charts/helmfile.d/admin/eqiad/; kube_env admin eqiad; ./cluster-helmfile.sh -i apply
  • Then the final step, namely deploying the new service:
    • On deploy1002: cd /srv/deployment-charts/helmfile.d/services/YOUR-SERVICE-NAME-HERE; helmfile -e codfw -i apply
    • On deploy1002: cd /srv/deployment-charts/helmfile.d/services/YOUR-SERVICE-NAME-HERE; helmfile -e eqiad -i apply

The service can now be accessed via the registered port on any of the kubernetes nodes (for manual testing).

If you need the service to be easily accessible from outside of the cluster, you might want to add Add a new load balanced service.

Rebooting a worker node

The unpolite way

To reboot a worker node, you can just reboot it in our environment. The platform will understand the event and respawn the pods on other nodes. However the system does not automatically rebalance itself currently (pods are not rescheduled on the node after it has been rebooted)

The polite way (recommended)

If you feel like being more polite, use kubectl drain, it will configure the worker node to no longer create new pods and move the existing pods to other workers. Draining the node will take time. Rough numbers on 2019-12-11 are at around 60 seconds.

# kubectl drain --ignore-daemonsets kubernetes1001.eqiad.wmnet
# kubectl describe pods  --all-namespaces | awk  '$1=="Node:" {print $NF}' | sort -u
kubernetes1002.eqiad.wmnet/10.64.16.75
kubernetes1003.eqiad.wmnet/10.64.32.23
kubernetes1004.eqiad.wmnet/10.64.48.52
kubernetes1005.eqiad.wmnet/10.64.0.145
kubernetes1006.eqiad.wmnet/10.64.32.18
# kubectl get nodes
NAME                         STATUS                     ROLES     AGE       VERSION
kubernetes1001.eqiad.wmnet   Ready,SchedulingDisabled   <none>    2y352d    v1.12.9
kubernetes1002.eqiad.wmnet   Ready                      <none>    2y352d    v1.12.9
kubernetes1003.eqiad.wmnet   Ready                      <none>    2y352d    v1.12.9
kubernetes1004.eqiad.wmnet   Ready                      <none>    559d      v1.12.9
kubernetes1005.eqiad.wmnet   Ready                      <none>    231d      v1.12.9
kubernetes1006.eqiad.wmnet   Ready                      <none>    231d      v1.12.9

When the node has been rebooted, it can be configured to reaccept pods using kubectl uncordon, e.g.

# kubectl uncordon kubernetes1001.eqiad.wmnet
# kubectl get nodes
NAME                         STATUS    ROLES     AGE       VERSION
kubernetes1001.eqiad.wmnet   Ready     <none>    2y352d    v1.12.9
kubernetes1002.eqiad.wmnet   Ready     <none>    2y352d    v1.12.9
kubernetes1003.eqiad.wmnet   Ready     <none>    2y352d    v1.12.9
kubernetes1004.eqiad.wmnet   Ready     <none>    559d      v1.12.9
kubernetes1005.eqiad.wmnet   Ready     <none>    231d      v1.12.9
kubernetes1006.eqiad.wmnet   Ready     <none>    231d      v1.12.9

The pods are not rebalanced automatically, i.e. the rebooted node is free of pods initially.

Restarting specific components

kube-controller-manager and kube-scheduler are components of the API server. In production multiple ones run and perform via the API an election to determine which one is the master. Restarting both is without grave consequences so it's safe to do. However both are critical components in as such that there are required for the overall cluster to function smoothly. kube-scheduler is crucial for node failovers, pod evictions, etc while kube-controller-manager packs multiple controller components and is critical for responding to pod failures, depools etc.

commands would be

sudo systemctl restart kube-controller-manager
sudo systemctl restart kube-scheduler

Restarting the API server

It's behind LVS in production, it's fine to restart it as long as enough time is given between the restarts across the cluster.

sudo systemctl restart kube-apiserver


Switch the active staging cluster (eqiad<->codfw)

We do have one staging cluster per DC, mostly to separate staging of kubernetes and components from staging of the services running on top of it. To provide staging services during work on one of the clusters, we can (manually) switch between the DCs:

Managing pods, jobs and cronjobs

Commands should be run from the deployment servers (at the time of this writing deploy1002).

You need to set the the correct context, for example:

kube_env admin eqiad

Other choices are codfw, staging-eqiad and staging-codfw.

The management commands is called kubectl.

Listing cronjobs, jobs and pods

kubectl get cronjobs -n <namespace>
kubectl get jobs -n <namespace>
kubectl get pods -n <namespace>

Deleting a job

kubectl delete job <job id>

Updating the docker image run by a CronJob

The relationship between the resources is the following:

Cronjob --spawns--> Job(s) --spawns--> Pod(s)

Note: Technically speaking, it's a tight control loop that lives in kube-controller-manager that does the spawning part, but adding that to the above would make this more confusing.

Under normal conditions a docker image version will be updated when a new deploy happens. The cronjob will have the new version. However, already created jobs by the CronJob will not be stopped until they have run to completion.

When the job finishes, the cronjob will create new job(s), which in turn will create new pod(s).

Depending on the correlation between a CronJob scheduling and the job run time there might be a window of time where despite the new deployment, the old job is still running.

Deleting the kubernetes pod created by the job itself will NOT work, i.e. the job will still exist and it will create a new pod (which will still have the old image).

So, if we are dealing with a long running kubernetes Job one can get the same effect by deleting the kubernetes job created by the cronjob.

phab:T280076 is an example where this was needed.

Checking which image version a cronjob is using

kubectl describe pod <pod in question>

(look for Image:)

See also

Toolforge Info