A metric can be a Prometheus metric

[mtneug]

Description

One monitoring solutions that has gotten a lot of attention in the container ecosystem is Prometheus. It defines formats for pull based metric gathering that spate can also use for autoscaling.

Design

Prometheus metric have the metric type prometheus. To function correctly additional labels have to be specified. In particular spate needs to know the HTTP url exposing the metrics, the name of the metric, and the kind (see #6) as well as the target value (see #10). localhost in urls refers to individual replicas. This is especially necessary for replica metrics, as there each replica needs to be queried individually. If localhost is not used as the host part and the metric is a replica metric, a warning should be logged. If localhost is used and the metric is a system metric any replica is used for querying. If HTTPS is used the full certificate validation must succeed. There is no option for turning this off. The name must be a valid Prometheus metric name. If more than one Prometheus metric with the exact same url and name is declared, autoscaling is deactivated and an error is logged.

$ docker service create \
   --name service \
   --label de.mtneug.spate.metrics.mymetric.type=prometheus \
   --label de.mtneug.spate.metrics.mymetric.kind=replica \
   --label de.mtneug.spate.metrics.mymetric.prometheus.endpoint=http://localhost:8080/metrics \
   --label de.mtneug.spate.metrics.mymetric.prometheus.name=mymetric \
   --label de.mtneug.spate.metrics.mymetric.target=20 \
   ...
   my/service