RedisWriter: publish Icinga 2 stats as a simple "keepalive"

Use case: a reader subscribes to config changes. As they happen rarely, chances
are good that the connection will time out in the meantime. Now, a reconnect is
easy - but you wouldn't know whether you missed any config changes. So you are
required to issue a new sync to be on the safe side. Given a 60sec connection
timeout (think: SSL layer, firewalls etc) when no traffic happens this would be
too expensive.

Some kind of a heartbeat available for subscription would allow subscribers to
artificially keep the connection alive. As a first simple solution to this I'd
suggest to publish CIB data, that might be useful anyways.

refs #4991
fixes #5098

Signed-off-by: Michael Friedrich <michael.friedrich@icinga.com>

lib/redis/rediswriter.cpp

@@ -21,6 +21,7 @@
 #include "redis/rediswriter.tcpp"
 #include "remote/eventqueue.hpp"
 #include "base/json.hpp"
+#include "base/statsfunction.hpp"
 
 using namespace icinga;
 
@@ -55,6 +56,11 @@ void RedisWriter::Start(bool runtimeCreated)
 	m_SubscriptionTimer->OnTimerExpired.connect(boost::bind(&RedisWriter::UpdateSubscriptionsTimerHandler, this));
 	m_SubscriptionTimer->Start();
 
+	m_StatsTimer = new Timer();
+	m_StatsTimer->SetInterval(10);
+	m_StatsTimer->OnTimerExpired.connect(boost::bind(&RedisWriter::PublishStatsTimerHandler, this));
+	m_StatsTimer->Start();
+
 	boost::thread thread(boost::bind(&RedisWriter::HandleEvents, this));
 	thread.detach();
 }
@@ -202,6 +208,28 @@ void RedisWriter::UpdateSubscriptions(void)
 	    << "Current Redis event subscriptions: " << m_Subscriptions.size();
 }
 
+void RedisWriter::PublishStatsTimerHandler(void)
+{
+	m_WorkQueue.Enqueue(boost::bind(&RedisWriter::PublishStats, this));
+}
+
+void RedisWriter::PublishStats(void)
+{
+	AssertOnWorkQueue();
+
+	if (!m_Context)
+		return;
+
+	//TODO: Figure out if more stats can be useful here.
+	StatsFunction::Ptr func = StatsFunctionRegistry::GetInstance()->GetItem("CIB");
+	Dictionary::Ptr status = new Dictionary();
+	Array::Ptr perfdata = new Array();
+	func->Invoke(status, perfdata);
+	String jsonStats = JsonEncode(status);
+
+	ExecuteQuery({ "PUBLISH", "icinga:stats", jsonStats });
+}
+
 void RedisWriter::HandleEvents(void)
 {
 	String queueName = Utility::NewUniqueID();

lib/redis/rediswriter.hpp

@@ -58,6 +58,8 @@ private:
 
 	void UpdateSubscriptionsTimerHandler(void);
 	void UpdateSubscriptions(void);
+	void PublishStatsTimerHandler(void);
+	void PublishStats(void);
 
 	/* config & status dump */
 	void UpdateAllConfigObjects(void);
@@ -86,6 +88,7 @@ private:
 
 	boost::shared_ptr<redisReply> ExecuteQuery(const std::vector<String>& query);
 
+	Timer::Ptr m_StatsTimer;
 	Timer::Ptr m_ReconnectTimer;
 	Timer::Ptr m_SubscriptionTimer;
 	WorkQueue m_WorkQueue;