diff --git a/README.md b/README.md
index 2e0d79e..3e3661d 100644
--- a/README.md
+++ b/README.md
@@ -1,9 +1,9 @@
 Fly Autoscaler
 ==============
 
-A metrics-based autoscaler for Fly.io. The autoscaler supports polling for
-metrics from a Prometheus instance and then computing the number of machines
-based on those metrics.
+The project is a metrics-based autoscaler for Fly.io. The autoscaler supports
+polling for metrics from a Prometheus instance and then computing the number of
+machines based on those metrics.
 
 ## How it works
 
@@ -63,36 +63,78 @@ machines available for a Fly app.
 
 ## Usage
 
+### Create an app for your autoscaler
+
+First, create an app for your autoscaler:
+
+```sh
+$ fly apps create my-autoscaler
+```
+
+Then create a `fly.toml` for the deployment. Update the `TARGET_APP_NAME` with
+the name of the app that you want to scale and update `MY_ORG` to the
+organization where your Prometheus metrics live.
+
+```toml
+app = "my-autoscaler"
+
+[build]
+image = "flyio/fly-autoscaler:0.1"
+
+[env]
+FAS_APP_NAME = "TARGET_APP_NAME"
+FAS_EXPR = "ceil(queue_depth / 10)"
+FAS_PROMETHEUS_ADDRESS = "https://api.fly.io/prometheus/MY_ORG"
+FAS_PROMETHEUS_METRIC_NAME = "queue_depth"
+FAS_PROMETHEUS_QUERY = "sum(queue_depth)"
+
+[metrics]
+port = 9090
+path = "/metrics"
+```
+
+
 ### Create a deploy token
 
-First, set up a new deploy token for your application so that the autoscaler
-and fetch metrics and start machines with it:
+Next, set up a new deploy token for the application you want to scale:
+
+```sh
+$ fly tokens create deploy -a TARGET_APP_NAME
+```
+
+Set the token as a secret on your application:
+
+```
+$ fly secrets set FAS_API_TOKEN="FlyV1 ..."
+```
+
+
+### Create a read-only token
+
+Create a token for reading your Prometheus data:
 
 ```sh
-$ fly tokens create deploy -a MYAPP -n "fly-autoscaler"
+$ fly tokens create readonly
 ```
 
-You can use this token by exporting it to an environment variable:
+Set the token as a secret on your application:
 
 ```
-$ export FLY_ACCESS_TOKEN="FlyV1 ..."
+$ fly secrets set FAS_PROMETHEUS_TOKEN="FlyV1 ..."
 ```
 
-### Running the server
+### Deploy the server
 
-To run the autoscaler as a server process, use the `serve` command. For example,
-this will ensure that there are always 5 instances running at a time:
+Finally, deploy your autoscaler application:
 
 ```sh
-$ fly-autoscaler serve \
-  -org MYORG \
-  -app MYAPP \
-  -prometheus.address "https://api.fly.io/prometheus/MYORG"
-  -prometheus.query "sum(fly_instance_up{app='MYAPP'})" \
-  -prometheus.metric-name instance_up
-  -expr "max(instance_up, 5)"
+$ fly deploy
 ```
 
+This should create a new machine and start it with the `fly-autoscaler` server
+running.
+
+
 ### Testing your metrics & expression
 
 You can perform a one-time run of metrics collection & expression evaluation for
@@ -101,11 +143,22 @@ perform any scaling of Fly Machines. It will only print the evaluated expression
 based on current metrics numbers.
 
 ```sh
-$ fly-autoscaler eval \
-  -org MYORG \
-  -app MYAPP \
-  -prometheus.address "https://api.fly.io/prometheus/MYORG"
-  -prometheus.query "sum(fly_instance_up{app='MYAPP'})" \
-  -prometheus.metric-name instance_up
-  -expr "max(instance_up, 5)"
+$ fly-autoscaler eval
 ```
+
+You can change the evaluated expression by setting the `FAS_EXPR` environment
+variable:
+
+```sh
+$ FAS_EXPR=queue_depth fly-autoscaler eval
+```
+
+## Configuration
+
+You can also configure `fly-autoscaler` with a YAML config file if you don't
+want to use environment variables or if you want to configure more than one
+metric collector.
+
+Please see the reference [fly-autoscaler.yml][] for more details.
+
+[fly-autoscaler.yml]: ./cmd/fly-autoscaler/testdata/fly-autoscaler.yml
diff --git a/cmd/fly-autoscaler/main_test.go b/cmd/fly-autoscaler/main_test.go
new file mode 100644
index 0000000..04cf76e
--- /dev/null
+++ b/cmd/fly-autoscaler/main_test.go
@@ -0,0 +1,48 @@
+package main_test
+
+import (
+	"testing"
+	"time"
+
+	main "github.com/superfly/fly-autoscaler/cmd/fly-autoscaler"
+)
+
+func TestConfig_Parse(t *testing.T) {
+	var config main.Config
+	if err := main.ParseConfigFromFile("../../etc/fly-autoscaler.yml", &config); err != nil {
+		t.Fatal(err)
+	}
+
+	if got, want := config.AppName, "TARGET_APP_NAME"; got != want {
+		t.Fatalf("AppName=%v, want %v", got, want)
+	}
+	if got, want := config.Expr, "ceil(queue_depth / 10)"; got != want {
+		t.Fatalf("Expr=%v, want %v", got, want)
+	}
+	if got, want := config.Interval, 15*time.Second; got != want {
+		t.Fatalf("Interval=%v, want %v", got, want)
+	}
+	if got, want := config.APIToken, "FlyV1 ..."; got != want {
+		t.Fatalf("APIToken=%v, want %v", got, want)
+	}
+	if got, want := config.Verbose, false; got != want {
+		t.Fatalf("Verbose=%v, want %v", got, want)
+	}
+
+	mc := config.MetricCollectors[0]
+	if got, want := mc.Type, "prometheus"; got != want {
+		t.Fatalf("MC[0].Type=%v, want %v", got, want)
+	}
+	if got, want := mc.MetricName, "queue_depth"; got != want {
+		t.Fatalf("MC[0].MetricName=%v, want %v", got, want)
+	}
+	if got, want := mc.Address, "https://api.fly.io/prometheus/MY_ORG"; got != want {
+		t.Fatalf("MC[0].Address=%v, want %v", got, want)
+	}
+	if got, want := mc.Query, "sum(queue_depth)"; got != want {
+		t.Fatalf("MC[0].Query=%v, want %v", got, want)
+	}
+	if got, want := mc.Token, "FlyV1 ..."; got != want {
+		t.Fatalf("MC[0].Token=%v, want %v", got, want)
+	}
+}
diff --git a/etc/fly-autoscaler.yml b/etc/fly-autoscaler.yml
new file mode 100644
index 0000000..57db9d8
--- /dev/null
+++ b/etc/fly-autoscaler.yml
@@ -0,0 +1,29 @@
+# The name of the target app that you want to scale.
+app-name: "TARGET_APP_NAME"
+
+# An expression to calculate the number of machines of the target app that
+# should be in a "started" state. Should return a number which will be rounded.
+# 
+# This uses the Expr language to define expressions: https://expr-lang.org/
+expr: "ceil(queue_depth / 10)"
+
+# The frequency that the reconciliation loop will be run.
+interval: "15s"
+
+# A Fly.io auth token that has permission to start machines for the target app.
+# This is typically set via the FAS_API_TOKEN environment variable.
+api-token: "FlyV1 ..."
+
+# If true, enables verbose debugging logging.
+verbose: false
+
+# Metric collectors fetch the current metrics when a reconciliation is performed.
+#
+# They store the current value locally with a given metric name so that the
+# expression can be used to calculate the machine count.
+metric-collectors:
+  - type: "prometheus"
+    metric-name: "queue_depth"
+    address: "https://api.fly.io/prometheus/MY_ORG"
+    query: "sum(queue_depth)"
+    token: "FlyV1 ..."