faas-idler

Scale OpenFaaS functions to zero replicas after a period of inactivity

Premise: functions (Deployments) can be scaled to 0/0 replicas from 1/1 or N/N replicas when they are not receiving traffic. Traffic is observed from Prometheus metrics collected in the OpenFaaS API Gateway.

Scaling to zero requires an "un-idler" or a blocking HTTP proxy which can reverse the process when incoming requests attempt to access a given function. This is done through the OpenFaaS API Gateway through which every incoming call passes - see Add feature: scale from zero to 1 replicas #685.

faas-idler is implemented as a controller which polls Prometheus metrics on a regular basis and tries to reconcile a desired condition - i.e. zero replicas -> scale down API call.

Building

The build requires Docker and builds a local Docker image.

TAG=0.2.0 make build
TAG=0.2.0 make push

Usage

Quick start

Swarm:

docker stack deploy func -c docker-compose.yml

Kubernetes

The faas-idler is installed as part of the helm chart, make sure that you pass the argument "--set faasIdler.dryRun=false" if you want the idler to go live and make changes to the API.

Activating a function for scale to zero

Now decorate some functions with the label: com.openfaas.scale.zero: "true" and watch the idler scale them to zero. You should also change the -dry-run flag to false. For example:

faas-cli store deploy figlet --label "com.openfaas.scale.zero=true"

Or if using the openfaas-operator and CRD:

...
spec:
  labels:
    com.openfaas.scale.zero: "true"
...

Configuration

• Environmental variables:

On Kubernetes the gateway_url needs to contain the suffix of the namespace you picked at deploy time. This is usually .openfaas and is pre-configured with a default.

Try using the ClusterIP/Cluster Service instead and port 8080.

env_var	description
gateway_url	The URL for the API gateway i.e. http://gateway:8080 or http://gateway.openfaas:8080 for Kubernetes
prometheus_host	host for Prometheus
prometheus_port	port for Prometheus
inactivity_duration	i.e. 15m (Golang duration)
reconcile_interval	i.e. 1m (default value)
secret_mount_path	default /var/secrets/, path from which basic-auth-user and basic-auth-password files are read
write_debug	default false, set to true to enable verbose logging for debugging / troubleshooting

• Command-line args

-dry-run - don't send scaling event

How it works:

gateway_function_invocation_total is measured for activity over duration i.e. 1h of inactivity (or no HTTP requests)

Logs

You can view the logs to show reconciliation in action.

kubectl logs -n openfaas -f deploy/faas-idler