Auto-scaling in OpenFaaS allows a function to scale up or down depending on demand represented by different metrics.
Scaling by requests per second¶
OpenFaaS ships with a single auto-scaling rule defined in the mounted configuration file for AlertManager. AlertManager reads usage (requests per second) metrics from Prometheus in order to know when to fire an alert to the API Gateway.
The API Gateway handles AlertManager alerts through its
The auto-scaling provided by this method can be disabled by either deleting the AlertManager deployment or by scaling the deployment to zero replicas.
The AlertManager rules (alert.rules) for Swarm can be viewed here and altered as a configuration map.
All calls made through the gateway whether to a synchronous function
/function/ route or via the asynchronous
/async-function route count towards this method of auto-scaling.
The minimum (initial) and maximum replica count can be set at deployment time by adding a label to the function.
com.openfaas.scale.minBy default this is set to
com.openfaas.scale.maxThe current default value is
20for 20 replicas
com.openfaas.scale.factorBy default this is set to
20%and has to be a value between 0-100 (including borders)
com.openfaas.scale.maxto the same value, allows to disable the auto-scaling functionality of openfaas. Setting
com.openfaas.scale.factor=0also allows to disable the auto-scaling functionality of openfaas.
For each alert fired the auto-scaler will add a number of replicas, which is a defined percentage of the max replicas. This percentage can be set using
com.openfaas.scale.factor. For example setting
com.openfaas.scale.factor=100 will instantly scale to max replicas. This label enables to define the overall scaling behavior of the function.
Note: Active alerts can be viewed in the "Alerts" tab of Prometheus which is deployed with OpenFaaS.
Scaling by CPU and/or memory utilization¶
When using Kubernetes the built-in Horizontal Pod Autoscaler (HPA) can be used instead of AlertManager.
Find out more in Stefan Prodan's blog post below: