extatus v0.2.1 Extatus
Extatus is an application to report the status of GenServer
processes to
Prometheus (time series database) via the HTTP endpoint /metrics
implemented with :cowboy
.
The metrics :cowboy_scrape_duration_seconds
(summary) and
cowboy_scrape_size_bytes
(summary) are calculated on every request to
the /metrics
endpoint.
Also for every instrumented GenServer
process, extatus reports the
metric :extatus_process_activity
(gauge). This metric indicates that a
process is up (2), down (0) or idle (1) depending on its value.
Example
To instrument a GenServer
is necessary to use the Extatus.Process
behaviour and implement its callbacks (gen_name/1
and report/1
) which
receive the current GenServer
state as argument. So, for the following
module:
defmodule Uninstrumented do
use GenServer
def start_link, do: GenServer.start_link(__MODULE__, nil)
def stop(pid), do: GenServer.stop(pid)
def value(pid), do: GenServer.call(pid, :value)
def inc(pid), do: GenServer.call(pid, :inc)
def dec(pid), do: GenServer.call(pid, :dec)
def init(_), do: {:ok, 0}
def handle_call(:value, _from, n), do: {:reply, {:ok, n}, n}
def handle_call(:inc, _from, n), do: {:reply, :ok, n + 1}
def handle_call(:dec, _from, n), do: {:reply, :ok, n - 1}
def handle_call(_, n), do: {:noreply, n}
end
And the instrumented GenServer
would be the following:
defmodule Instrumented do
use GenServer
use Extatus.Process # Extatus.Process behaviour
def start_link, do: GenServer.start_link(__MODULE__, nil)
def stop(pid), do: GenServer.stop(pid)
def value(pid), do: GenServer.call(pid, :value)
def inc(pid), do: GenServer.call(pid, :inc)
def dec(pid), do: GenServer.call(pid, :dec)
# Metric
defmetrics do
gauge :instrument_gauge do
label :label
registry :default
help "Instrument gauge"
end
end
# Name of the process. This must be unique.
def get_name(_n), do: {:ok, "instrumented_process"}
# Report
def report(n) do
Gauge.set(:instrument_gauge, [label: "Label"], n)
end
def init(_) do
{:ok, _} = Extatus.set(__MODULE__, self()) # Add extatus handler.
{:ok, 0}
end
def handle_call(:value, _from, n), do: {:reply, {:ok, n}, n}
def handle_call(:inc, _from, n), do: {:reply, :ok, n + 1}
def handle_call(:dec, _from, n), do: {:reply, :ok, n - 1}
def handle_call(_, n), do: {:noreply, n}
end
This GenServer
will report the current value stored in the server as the
metric :instrument_gauge
to Prometheus.
Additionally, Yggdrasil
subscriptions to the channel:
%Yggdrasil.Channel{name: :extatus, adapter: Yggdrasil.Elixir}
can be used to get the updates on the current state of the process i.e:
iex> chan = %Yggdrasil.Channel{name: :extatus, adapter: Yggdrasil.Elixir}
iex> Yggdrasil.subscribe(chan)
iex> flush()
{:Y_CONNECTED, (...)}
iex> {:ok, _} = Instrumented.start_link()
{:ok, #PID<0.603.0>}
iex> flush()
{:Y_EVENT, _, %Extatus.Message{name: "instrumented_process", state: :up}}
Configuration
The following are the configuration arguments available:
:timeout
- Frequency the handlers get the metrics from the processes.:port
- Port where cowboy is listening to request coming from Prometheus.:prometheus_registry
- Prometheus registry. By default is:default
.
i.e:
config :extatus,
timeout: 5000,
port: 1337,
prometheus_registry: :test
Summary
Functions
Starts a status handler for the provided module
and pid
. Links to
calling process. This is to avoid having processes without Extatus handlers
Functions
Starts a status handler for the provided module
and pid
. Links to
calling process. This is to avoid having processes without Extatus handlers.