misc(http): Adding a simple http endpoint for liveness checks (#1760)

* misc(http): Adding a simple http endpoint for liveness checks

http/src/main/scala/filodb/http/HealthRoute.scala

@@ -48,6 +48,12 @@ class HealthRoute(coordinatorActor: ActorRef, v2ClusterEnabled: Boolean, setting
           }
         }
       }
+    } ~
+    // Adding a simple liveness endpoint to check if the FiloDB instance is reachable or not
+    path ("__liveness") {
+      get {
+        complete(httpLiveness("UP"))
+      }
     }
   }
 }

http/src/main/scala/filodb/http/apiv1/HttpSchema.scala

@@ -2,6 +2,12 @@ package filodb.http.apiv1
 
 // Prometheus API compatible response envelopes
 sealed trait HttpSuccess
+
+/**
+ * Schema for http liveness checks
+ * @param Status
+ */
+final case class HttpLiveness(Status: String) extends HttpSuccess
 final case class HttpList[A](status: String, data: Seq[A]) extends HttpSuccess
 final case class HttpError(errorType: String,
                            error: String,
@@ -14,6 +20,8 @@ object HttpSchema {
   def httpErr(exception: Exception): HttpError =
     HttpError(exception.getClass.getName, exception.getMessage,
               stackTrace = exception.getStackTrace.toSeq.map(_.toString))
+
+  def httpLiveness(status: String): HttpLiveness = HttpLiveness(status)
 }
 
 final case class HttpShardState(shard: Int, status: String, address: String)