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Autoscaling in Kubernetes
- 1. An implementation primer ContainerConf 2018 Bangalore Autoscaling in Kubernetes
- 2. Hrishikesh Deodhar Director of Engineering InfraCloud technologies www.infracloud.io https://www.linkedin.com/in/hrishikesh-deodhar https://twitter.com/Hrishi_kesh_ Containers | DevOps | Cloud | Kubernetes
- 3. Auto of Scale ● Autoscaling: Why & what? ● What to scale in Kubernetes ○ Pods ○ Nodes ● Pod scaling ○ Metric Server ○ HPA controller ○ Monitoring pipeline ● Node Scaling ○ Kubernetes Autoscaler ○ Escalator
- 4. As explained to a 5 year old Image Source: http://blog.infracloud.io/kubernetes-autoscaling-explained/ Capacity of current app With single instance User Requests Your current VM/Pod/Container A spare instance so that load can be shared
- 5. ● Horizontally Scale ○ Applications to meet user demand ○ Nodes to meet infrastructure demand (Of applications) Autoscaling: what?
- 6. ● Match: Actual usage == Current Usage ● Use elasticity of cloud effectively ● Optimize Cost Autoscaling: why?
- 7. Pod Autoscaling Let’s start with a demo
- 8. Horizontal Pod Autoscaler Controller Deployment Controller Kubelet KubeletcAdvisor Kubelet Pod Pod Pod Metrics ServerMetrics Aggregator Replica set Resource Metrics from Pods Pod Autoscaling (What just happened earlier...) Prometheus Adapter Prometheus Custom Metrics Pod
- 10. Node Autoscaling ● Kubernetes AutoScaler (https://github.com/kubernetes/autoscaler) ● Escalator (https://github.com/atlassian/escalator) We will talk about Kubernetes Autoscaler
- 11. Kubernetes Autoscaler: Basics ● A controller inside Kubernetes Cluster ● Increases Cluster Size when: ○ Pods in pending state due to insufficient resources ● Decreases Cluster Size when: ○ Cluster resource consumption is low for sufficient duration
- 12. Kubernetes Autoscaler: Safety first! Won’t evict nodes if: ● PodDisruptionBudget is restrictive ● Pod can not be moved because of affinity/node selector rules ● Kube-system pods running ● Pods with local storage ● Pods with annotation: "cluster-autoscaler.kubernetes.io/safe-to-evict": "false"
- 13. Clusters can be complicated business! Availability Zone 1 Availability Zone 3 Availability Zone 2 Node Pool 1 (CPU Intensive) ● Scaling happens at node pool level ● Can be done across AZs ● “Expanders” can be used for different strategies Node Pool 2 (Mem Intensive) Node Pool 2 (GPU - ML/DL)
- 14. HPA & Autoscaler: Marriage made in heaven Pods & Nodes scale down After the load goes down, pods are evicted. This leads to under utilization of nodes and node is evicted HPA Scales Pods HPA scales the pods based on HPA definitions. More pods are are scheduled and some of them go in pending state Autoscaler Kicks in Cluster autoscaler adds more nodes based on pending pods and pods start running HPA and cluster scaling working together
- 15. Recommendations From a real world implementation
- 16. Scaling speed The delay between two consecutive up/down scale in HPA is configured at cluster level (Current upscale delay at 3m). Based on how fast you need to scale, this should be configured at cluster level. Similar controls exist for node autoscaler
- 17. Scaling metric Every workload is different, some should be scaled on CPU, some on number of messages in queue, some on a different metric outside of application. Choose your “scaling metric” carefully!
- 18. Monitoring Adapters If you are using a commercial monitoring tool - you will have to route metrics to metric server. You can also build not to depend on outage of a SaaS monitoring tool! Also check you have adapter from monitoring tool to Metric server!
- 19. State & Scaling Statefulset scaling is very different - you need to provision volume etc. and depending on underlying datastore, might need initial data bootstrapping etc
- 20. Further reading ● Metrics Server (https://github.com/kubernetes-incubator/metrics-server) ● https://github.com/infracloudio/kubernetes-autoscaling ● https://kubernetes.io/docs/tasks/run-application/horizontal-pod-autoscale/ ● https://github.com/kubernetes/autoscaler/blob/master/cluster-autoscaler/FAQ.md
Notas del editor
- Autoscaling in kubernetes has 2 dimensions: Pod autoscaling or workload autoscaling and Cluster autoscaling, autoscaling your cluster hosts to provide more compute. Why do you need autoscaling? Well why not? When you setup your kubernetes cluster to run your containerized workloads, the setup typically takes into consideration, the load that is being expected on the cluster, number of users which will utilize the application, what kind of application do you serve and several other factors.
- Autoscaling in kubernetes has 2 dimensions: Pod autoscaling or workload autoscaling and Cluster autoscaling, autoscaling your cluster hosts to provide more compute. Why do you need autoscaling? Well why not? When you setup your kubernetes cluster to run your containerized workloads, the setup typically takes into consideration, the load that is being expected on the cluster, number of users which will utilize the application, what kind of application do you serve and several other factors.
- Horizontal Pod Autoscaling : It is a kubernetes resource and is implemented as a controller. Control loop can be controlled by the --horizontal-pod-autoscaler-sync-period flag. Dynamically control the replicas of the pods based on a defined objective such as the CPU usage being X % The HorizontalPodAutoscaler normally fetches metrics from a series of aggregated APIs (metrics.k8s.io, custom.metrics.k8s.io, and external.metrics.k8s.io) There are 2 kinds of metrics that the HPA can act upon. Per-pod resource metrics. (These are the metrics fetched from the resource metrics API for each pod. Metrics such as cpu, memory are targetted in this case) Per-pod Custom metrics. (These are the metrics that are reported by your monitoring pipeline in this case prometheus, these would change from a case by case basis since metrics for scaling would be different for different implementations)
- Cluster Autoscaler is a tool that automatically adjusts the size of the Kubernetes cluster when: there are pods that failed to run in the cluster due to insufficient resources. some nodes in the cluster are so underutilized, for an extended period of time, that they can be deleted and their pods will be easily placed on some other, existing nodes.