Tune prometheus default intervals and block durations

This increases the default scrape and evaluation intervals to match
those of the prometheus service upstream with the aim to reduce
prometheus's resource consumption. It also adds configuration
parameters for the min and max block durations that series can
span

Change-Id: I7f9352413a273fbf680b892ba26e30cf27bae232

prometheus/templates/bin/_prometheus.sh.tpl

@@ -26,6 +26,8 @@ function start () {
     --query.max-concurrency={{ .Values.conf.prometheus.query.max_concurrency }} \
     --storage.tsdb.path={{ .Values.conf.prometheus.storage.tsdb.path }} \
     --storage.tsdb.retention={{ .Values.conf.prometheus.storage.tsdb.retention }} \
+    --storage.tsdb.min-block-duration={{ .Values.conf.prometheus.storage.tsdb.min_block_duration }} \
+    --storage.tsdb.max-block-duration={{ .Values.conf.prometheus.storage.tsdb.max_block_duration }} \
     {{ if .Values.conf.prometheus.web_admin_api.enabled }}
     --web.enable-admin-api \
     {{ end }}

prometheus/values.yaml

@@ -189,6 +189,8 @@ conf:
       tsdb:
         path: /var/lib/prometheus/data
         retention: 7d
+        min_block_duration: 2h
+        max_block_duration: 6h
     log:
       format: logger:stdout?json=true
       level: info
@@ -199,8 +201,8 @@ conf:
       enabled: false
     scrape_configs:
       global:
-        scrape_interval: 25s
-        evaluation_interval: 10s
+        scrape_interval: 60s
+        evaluation_interval: 60s
       rule_files:
         - /etc/config/rules/alertmanager.rules
         - /etc/config/rules/etcd3.rules