MXS-2219 Implement rudimentary Clustrix monitoring

The monitor now pings the health check ports of the Clustrix nodes.
A response translates to RUNNING and a non-response to DOWN.

server/modules/monitor/clustrixmon/clustrixmonitor.cc

@@ -13,9 +13,12 @@
 
 #include "clustrixmonitor.hh"
 
+namespace http = mxb::http;
+using namespace std;
 
 ClustrixMonitor::ClustrixMonitor(MXS_MONITOR* pMonitor)
     : maxscale::MonitorInstance(pMonitor)
+    , m_delayed_http_check_id(0)
 {
 }
 
@@ -25,6 +28,132 @@ ClustrixMonitor* ClustrixMonitor::create(MXS_MONITOR* pMonitor)
     return new ClustrixMonitor(pMonitor);
 }
 
+bool ClustrixMonitor::configure(const MXS_CONFIG_PARAMETER* pParams)
+{
+    m_health_urls.clear();
+
+    m_config.set_cluster_monitor_interval(config_get_integer(pParams, CLUSTER_MONITOR_INTERVAL_NAME));
+
+    MXS_MONITORED_SERVER* pMonitored_server = m_monitor->monitored_servers;
+
+    while (pMonitored_server)
+    {
+        SERVER* pServer = pMonitored_server->server;
+
+        string url(pServer->address);
+        url += ":";
+        url += "3581"; // TODO: Possibly make configurable.
+
+        m_health_urls.push_back(url);
+
+        pMonitored_server = pMonitored_server->next;
+    }
+
+    return true;
+}
+
+void ClustrixMonitor::pre_tick()
+{
+    m_http = mxb::http::get_async(m_health_urls);
+
+    if (m_http.status() == http::Async::ERROR)
+    {
+        MXS_WARNING("Could not initiate health check to nodes.");
+    }
+}
+
 void ClustrixMonitor::tick()
 {
+    switch (m_http.status())
+    {
+    case http::Async::PENDING:
+        MXS_WARNING("Health check round had not completed when next tick arrived.");
+        break;
+
+    case http::Async::ERROR:
+        MXS_WARNING("Health check round ended with general error.");
+    case http::Async::READY:
+        {
+            m_http = mxb::http::get_async(m_health_urls);
+
+            switch (m_http.status())
+            {
+            case http::Async::PENDING:
+                initiate_delayed_http_check();
+                break;
+
+            case http::Async::ERROR:
+                MXS_ERROR("Could not initiate health check.");
+                break;
+
+            case http::Async::READY:
+                MXS_NOTICE("Health check available immediately.");
+                break;
+            }
+        }
+    }
+}
+
+void ClustrixMonitor::initiate_delayed_http_check()
+{
+    mxb_assert(m_delayed_http_check_id == 0);
+
+    long max_delay_ms = m_monitor->interval / 10;
+
+    long ms = m_http.wait_no_more_than();
+
+    if (ms > max_delay_ms)
+    {
+        ms = max_delay_ms;
+    }
+
+    m_delayed_http_check_id = delayed_call(ms, &ClustrixMonitor::check_http, this);
+}
+
+bool ClustrixMonitor::check_http(Call::action_t action)
+{
+    m_delayed_http_check_id = 0;
+
+    if (action == Call::EXECUTE)
+    {
+        switch (m_http.perform())
+        {
+        case http::Async::PENDING:
+            initiate_delayed_http_check();
+            break;
+
+        case http::Async::READY:
+            {
+                const vector<http::Result>& results = m_http.results();
+
+                MXS_MONITORED_SERVER* pMonitored_server = m_monitor->monitored_servers;
+
+                for (size_t i = 0; i < m_health_urls.size(); ++i)
+                {
+                    mxb_assert(pMonitored_server);
+
+                    const auto& url = m_health_urls[i];
+                    const auto& result = results[i];
+
+                    MXS_INFO("%s: %s", url.c_str(), (result.code == 200) ? "OK" : result.body.c_str());
+
+                    uint64_t bits = 0;
+
+                    if (result.code == 200)
+                    {
+                        bits |= SERVER_RUNNING;
+                    }
+
+                    monitor_set_pending_status(pMonitored_server, bits);
+                    pMonitored_server = pMonitored_server->next;
+                }
+            }
+            break;
+
+        case http::Async::ERROR:
+            MXS_ERROR("Health check waiting ended with general error.");
+        }
+    }
+
+    return false;
 }