Contents:
- Introduction
- Why KubeScale instead of the Kubernetes HPA?
- Alerts of scaling decisions with explanation
- Configuration explained
- High level KubeScale algorithm
KubeScale is a hybrid auto-scaler primarily focused on horizontally scaling containerised applications deployed on Kubernetes. It automatically scales deployments on Kubernetes by predicting the future workload and adjusting the resources beforehand. The workload prediction is done using a Deep Autoregressive Recurrent Networks (implemented by GluonTS).
Some of the problems solved by the KubeScale auto-scaler are:
- how to minimise the wasting of computing resources and avoid resource over-provisioning
- how to maximise the performance of the application and avoid resource under-provisioning
- how to determine when to scale up and scale down
- how much to scale the resources
- how to anticipate rising or falling demand for computing resources
- ...
Existing metrics sources are:
- Requests per second
- CPU usage
To integrate a new source of metrics use the simple MetricSource interface. You should choose metrics that are likely to present the overall workload on the application.
Compared to the native Kubernetes horizontal pod auto-scaler, KubeScale:
- supports Prometheus as metrics source allowing you to avoid complicated integration with the metrics server
- predicts future metric values using time-series optimised deep recurrent neural networks
- allows greater fine tuning and control
KubeScale sends alerts regularly.
An example of an alert that the KubeScale auto-scaler sends:
KubeScale is very configurable and extensive, below is the default configuration explained. The most important parameter for tuning is the scaling metric that is going to be used for auto-scaling and the target value for that metric. The target value for an auto-scaling metric presents a trade-off between resource utilisation and quality of service. Targeting a lower resource usage ensures resources are sufficiently over-provisioned to reduce the likelihood that the quality of service deteriorates when there are sudden demand bursts.
# namespace and service name of Prometheus - we get the REST API host/port using this information
prometheus_namespace: cm
prometheus_svc_name: prometheus-release-server
# namespace and service name of the prometheus push gateway - used for storing the state of the autoscaler
pushgateway_namespace: cm
pushgateway_svc_name: prometheus-release-pushgateway
# email address of the person receiving the scaling events
notification_email_receiver: [email protected]
# used to identify the kubernetes deployment that has to be scaled
kubernetes:
# name of the space in which the resource is
namespace: default
# name of the deployment
deployment: pythonwebapp
# in case the resources pods have two containers, what is the name of one of the containers
container: pythonwebapp
# these configurations alter the behaviour of the auto-scaler
strategy:
# whether to scale based on reactive indications
# recommended to enable together with proactive mode to make the auto-scaler hybrid
reactive_scaling_enabled: true
# whether to scale based on proactive indications
# recommended to enable together with reactive mode to make the auto-scaler hybrid
proactive_scaling_enabled: true
# whether to down scale based on proactive indications -> usually it doesn't make sense to downscale if you expect
# that in eg. 10 minutes the
proactive_downscaling_enabled: false
# whether to only email forecasts and not actually scale the number of instances
proactive_mode_forecast_only: false
# whether to delay making proactive decision until min_train_data_history_hours of time passes.
# for cases where you expect that the pattern changed so much that the there isn't enough appropriate training data
delay_proactive_mode_by_min_train_data_history: false
# how often to run the control loop evaluation method, in seconds, minimum is 30 due to granularity of metrics
eval_time_interval_sec: 30
# minimum number of instances (pods) for that deployment
min_instances: 1
# maximum number of instances (pods) for that deployment
max_instances: 15
# how long to wait before a downscaling decision after any scaling decision
downscale_cooldown_period_min: 1
# how long to wait before a downscaling decision after a scaling up decision.
# usually this is set to a higher value than 'downscale_cooldown_period_min' to avoid the reactive component
# interfering with the proactive component that increases the resources ahead of time (as defined with the preempt_period_min parameter)
downscale_after_predictive_scaleup_cooldown_period_min: 3
# the period you want to make a scaling decision for
# eg. now you want to make a decision on what number of instances you should have in 30 seconds
preempt_period_min: 3
# maximum percentage that the auto-scaler can downscale at once eg. from 10 to 5 nodes
downscale_max_percentage: 20
forecasting:
# how often to forecast future values of the metric values - expensive operation due to having to train a predictive model (measured in minutes)
forecast_creation_interval_mins: 30
# for how long in future to forecast (measured in minutes). depends primarily on the type of workload and datasets
forecast_period_mins: 60
metrics:
# currently supported metrics (defined as per pod values) are:
# a) requests_per_second - number of requests per second handled by each instance
# b) cpu_usage - utilisation of the allowed CPU resources (as a percentage - so from 0 to 1)
load_metric_name: requests_per_second # must be same as scaling metric
# target value of the load metric for each instance
scaling_metric_target_value: 30
# if the threshold is breached on the other side by less than this amount, don't do anything
threshold_breach_tolerance: 5
# how much past data (metrics) have to be gathered (in seconds) - 43200 means 12 hours, 1 hour is 3600
min_train_data_history_hours: 2
# don't use more than this data for training - 604,800 means 7 days (3600 * 24 * 7). Max value is 14 days
max_train_data_history_hours: 8
# resolution of metrics - ie. when getting a time-series of metrics
# for which interval to get each of the metrics in minutes, minimal value is 1
# Gluon TS models don't support less than a 1 minute frequency
step_size_mins: 1
custom_params:
# necessary for the requests_per_second metric source to be able to get the relevant metric from the Envoy load balancer
# use it to similarly pass the configuration for other metric sources
cluster_name: pythonwebappThe high level algorithm behind KubeScale is the following:
Example of KubeScale and other auto-scalers in action shown through metrics produced using the related platform for evaluation of auto-scalers:
