Statistics and monitoring

Emissary collects many statistics internally, and makes it easy to direct this information to a statistics and monitoring tool of your choice. As an example, for a given service usersvc, here are some interesting statistics to investigate:

• envoy.cluster.usersvc.upstream_rq_total is the total number of requests that usersvc has received via Emissary. The rate of change of this value is one basic measure of service utilization, i.e. requests per second.
• envoy.cluster.usersvc.upstream_rq_2xx is the total number of requests to which usersvc responded with an HTTP response indicating success. This value divided by the prior one, taken on an rolling window basis, represents the recent success rate of the service. There are corresponding 4xx and 5xx counters that can help clarify the nature of unsuccessful requests.
• envoy.cluster.usersvc.upstream_rq_time is a StatsD timer that tracks the latency in milliseconds of usersvc from Emissary’s perspective. StatsD timers include information about means, standard deviations, and decile values.

Overriding Statistics Names

The optional stats_name element of every CRD that references a service (Mapping, TCPMapping, AuthService, LogService, RateLimitService, and TracingService) can override the name under which cluster statistics are logged (usersvc above). If not set, the default is the service value, with non-alphanumeric characters replaced by underscores:

• service: foo will just use foo
• service: foo:8080 will use foo_8080
• service: http://foo:8080 will use http___foo_8080
• service: foo.othernamespace will use foo_othernamespace

The last example is worth special mention: a resource in a different namespace than the one in which Emissary is running will automatically be qualified with the namespace of the resource itself. So, for example, if Emissary is running in the ambassador namespace, and this Mapping is present in the default namespace:

apiVersion: getambassador.io/v3alpha1
kind: Mapping
metadata:
  name: default-mapping
  namespace: default
spec:
  prefix: /default/
  service: default-service

then the service will be qualified to default-service.default, so the stats_name will be default_service_default rather than simply default_service. To change this behavior, set stats_name explicitly.

Monitoring Statistics

There are several ways to get different statistics out of Emissary:

• The :8877/metrics endpoint can be polled for aggregated statistics (in a Prometheus-compatible format). This is our recommended method.
• Emissary can push Envoy statistics over the StatsD or DogStatsD protocol.
• Emissary can push RateLimiting statistics over the StatsD protocol.

The Four Golden Signals

The Four Golden Signals are four generally-accepted metrics that are important to monitor for good information about service health:

Latency

The time it takes to service a request. cluster.$name.upstream_rq_time is a histogram of time taken by individual requests, which can be an effective latency metric.

Traffic

The amount of demand being placed on your system. cluster.$name.upstream_rq_active is a gauge that shows the number of active outstanding requests, which can be a good proxy for traffic.

Errors

The number of failing requests. Some errors (e.g. a request succeeds, but gives the wrong answer) can only be detected by application-specific monitoring; however, many errors can be spotted simply by looking at the HTTP status code of requests. cluster.$name.upstream_rq_5xx is a counter of HTTP 5xx responses, so monitoring it over time can show error rates. (Likewise, cluster.$name.upstream_rq_4xx exists.)

Saturation

The hardest metric to measure, saturation describes how much of the total capability of the system to respond to requests is being used. Fully measuring saturation often requires application-specific monitoring, but looking at the 99th percentile of latency over a short window - perhaps a a minute - can often give an early indication of saturation problems.