Rework how alias rotation is triggered

Instead of periodically running the rotation (every 5 minutes by
default), schedule rotation after startup and on day change.

In both case, wait a short delay (60 seconds, in order for some data to
be ingested by Riemann, downsampled by samplerr and persisted in the
corresponding ElasticSearch daily index) before we create aliases to make
the corresponding data available.

src/riemann/plugin/samplerr.clj

@@ -582,25 +582,18 @@
         (info "Creating samplerr aliases")
         (es/request conn (create-aliases-query indices index-prefix alias-prefix))))))
 
-(defn rotation-service-ng
-  "returns a service which schedules a task to rotate aliases"
-  [{:keys [interval conn alias-prefix index-prefix enabled?]
-    :or {interval (clj-time.core/minutes 5)
-         enabled? true}}]
-  (let [interval (to-millis interval)]
-    (service/thread-service
-      ::samplerr-rotation [interval conn alias-prefix index-prefix enabled?]
-      (fn rot [core]
-        (Thread/sleep interval)
-        (try
-          (if enabled?
-            (rotate-ng {:conn conn :index-prefix index-prefix :alias-prefix alias-prefix}))
-          (catch Exception e
-            (warn e "rotation service caught")))))))
-
 (defn periodically-rotate-ng
-    "adds an alias rotation service to core"
-  [& opts]
-  (info "registering rotation service with" (apply :interval opts) "interval")
-  (let [service (apply rotation-service-ng opts)]
-    (swap! riemann.config/next-core core/conj-service service :force)))
+  "Automatically maintain samplerr aliases"
+  [opts]
+  (let [rotation-interval 86400
+        rotation-delay 60
+        beginning-of-last-rotation-interval (* (quot (unix-time) rotation-interval) rotation-interval)
+        beginning-of-next-rotation-interval (riemann.time/next-tick beginning-of-last-rotation-interval rotation-interval)
+        daily-rotation-delay (+ beginning-of-next-rotation-interval rotation-delay)
+        do-rotate (fn [] (rotate-ng opts))]
+    (info (str "Scheduling bootime alias management in " rotation-delay " seconds"))
+    (riemann.time/after! rotation-delay do-rotate)
+    (info (str "Scheduling daily alias management at " (.format (java.text.SimpleDateFormat. "yyyy-MM-dd'T'HH:mm:ssXXX") (* 1000 daily-rotation-delay))))
+    (riemann.time/once!
+      daily-rotation-delay
+      (fn [] (riemann.time/every! rotation-interval do-rotate)))))