docker: adds alertmanager to prometheus fig

with an alert rule that will always fire

docker/blocks/prometheus/Dockerfile

 FROM prom/prometheus
 ADD prometheus.yml /etc/prometheus/
+ADD alert.rules /etc/prometheus/

docker/blocks/prometheus/alert.rules

+# Alert Rules
+
+ALERT AppCrash
+  IF process_open_fds > 0
+  FOR 15s
+  LABELS { severity="critical" }
+  ANNOTATIONS {
+   summary = "Number of open fds > 0",
+   description = "Just testing"
+  }

docker/blocks/prometheus/fig

@@ -18,3 +18,8 @@ fake-prometheus-data:
   environment:
     FD_DATASOURCE: prom
 
+alertmanager:
+  image: quay.io/prometheus/alertmanager
+  net: host
+  ports:
+    - "9093:9093"

docker/blocks/prometheus/prometheus.yml

@@ -6,9 +6,18 @@ global:
 
 # Load and evaluate rules in this file every 'evaluation_interval' seconds.
 rule_files:
+  - "alert.rules"
   # - "first.rules"
   # - "second.rules"
 
+alerting:
+  alertmanagers:
+  - scheme: http
+    static_configs:
+    - targets:
+      - "127.0.0.1:9093"
+
+
 # A scrape configuration containing exactly one endpoint to scrape:
 # Here it's Prometheus itself.
 scrape_configs: