Integrating prometheus with Policy components

With this change, all PF components can export prometheus metrics
by default. The prometheus metrics servlet will be running on
/metrics servletPath..
If the metrics shouldn't be exported, just add a flag
    "promethus": false
in the restServerParameters of default configuration file.
This brings up prometheus servlet on /metrics servletPath.

Also as part of standard servlet support, "servletUriPath" and
"servletClass" are 2 other fields added to RestServerParameters
which can be used to add standard servlets. This can be revisited later
if needed.
Basically, any servlet can be added by passing these fields, for
example, to add prometheus metrics servlet on /test/metrics,
add the below to restServerParameters:
    "servletUriPath": "/test/metrics",
    "servletClass": "io.prometheus.client.exporter.MetricsServlet"

In addition, we can later go to individual components and add more
metrics, say for e.g.,
deployedPoliciesCounter/undeployedPoliciesCounter etc on PAP,
executedEvents/failedEvents etc on PDP and so on.
This will look something like below, for e.g. in policy-pap component:
 io.prometheus.client.Counter counter = Counter.build()
  .name("policies_deployed_total")
  .help("Number of policies deployed.").register()
Whenever a policy is deployed, just call
 counter.inc()

Usage of code like above in the individual component will expose
such data as well as part of the exposed metrics.

Change-Id: Id667f27b15c012398421ba657b5324cc1d82cf1f
Issue-ID: POLICY-3524
Signed-off-by: a.sreekumar <ajith.sreekumar@bell.ca>
Signed-off-by: jhh <jorge.hernandez-herrero@att.com>
Signed-off-by: a.sreekumar <ajith.sreekumar@bell.ca>

1 files changed, 47 insertions, 2 deletions

diff --git a/policy-endpoints/src/main/java/org/onap/policy/common/endpoints/http/server/internal/JettyServletServer.java b/policy-endpoints/src/main/java/org/onap/policy/common/endpoints/http/server/internal/JettyServletServer.java
index e4b51372..c5af20cb 100644
--- a/policy-endpoints/src/main/java/org/onap/policy/common/endpoints/http/server/internal/JettyServletServer.java
+++ b/policy-endpoints/src/main/java/org/onap/policy/common/endpoints/http/server/internal/JettyServletServer.java
@@ -4,7 +4,7 @@
  * ================================================================================
  * Copyright (C) 2017-2021 AT&T Intellectual Property. All rights reserved.
  * Modifications Copyright (C) 2019-2020 Nordix Foundation.
- * Modifications Copyright (C) 2020 Bell Canada. All rights reserved.
+ * Modifications Copyright (C) 2020-2021 Bell Canada. All rights reserved.
  * ================================================================================
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -22,9 +22,15 @@
 
 package org.onap.policy.common.endpoints.http.server.internal;
 
+import io.prometheus.client.exporter.MetricsServlet;
+import io.prometheus.client.hotspot.DefaultExports;
 import java.util.EnumSet;
+import java.util.HashMap;
+import java.util.Map;
 import javax.servlet.DispatcherType;
+import javax.servlet.Servlet;
 import lombok.Getter;
+import lombok.NonNull;
 import lombok.ToString;
 import org.eclipse.jetty.security.ConstraintMapping;
 import org.eclipse.jetty.security.ConstraintSecurityHandler;
@@ -40,6 +46,7 @@ import org.eclipse.jetty.server.ServerConnector;
 import org.eclipse.jetty.server.Slf4jRequestLogWriter;
 import org.eclipse.jetty.servlet.FilterHolder;
 import org.eclipse.jetty.servlet.ServletContextHandler;
+import org.eclipse.jetty.servlet.ServletHolder;
 import org.eclipse.jetty.util.security.Constraint;
 import org.eclipse.jetty.util.security.Credential;
 import org.eclipse.jetty.util.ssl.SslContextFactory;
@@ -125,6 +132,11 @@ public abstract class JettyServletServer implements HttpServletServer, Runnable
     protected Thread jettyThread;
 
     /**
+     * Container for default servlets.
+     */
+    protected final Map<String, ServletHolder> servlets = new HashMap<>();
+
+    /**
      * Start condition.
      */
     @ToString.Exclude
@@ -209,6 +221,18 @@ public abstract class JettyServletServer implements HttpServletServer, Runnable
         context.addFilter(filterClass, tempFilterPath, EnumSet.of(DispatcherType.INCLUDE, DispatcherType.REQUEST));
     }
 
+    protected ServletHolder getServlet(@NonNull  Class<? extends Servlet> servlet, @NonNull  String servletPath) {
+        synchronized (servlets) {
+            return servlets.computeIfAbsent(servletPath, key -> context.addServlet(servlet, servletPath));
+        }
+    }
+
+    protected ServletHolder getServlet(String servletClass, String servletPath) {
+        synchronized (servlets) {
+            return servlets.computeIfAbsent(servletPath, key -> context.addServlet(servletClass, servletPath));
+        }
+    }
+
     /**
      * Returns the https connector.
      *
@@ -472,11 +496,32 @@ public abstract class JettyServletServer implements HttpServletServer, Runnable
     }
 
     @Override
-    public void addServletClass(String servletPath, String restClass) {
+    public void addServletClass(String servletPath, String servletClass) {
         throw new UnsupportedOperationException("addServletClass()" + NOT_SUPPORTED);
     }
 
     @Override
+    public void addStdServletClass(@NonNull String servletPath, @NonNull String plainServletClass) {
+        this.getServlet(plainServletClass, servletPath);
+    }
+
+    @Override
+    public void setPrometheus(String metricsPath) {
+        this.getServlet(MetricsServlet.class, metricsPath);
+        DefaultExports.initialize();
+    }
+
+    @Override
+    public boolean isPrometheus() {
+        for (ServletHolder servlet : context.getServletHandler().getServlets()) {
+            if (MetricsServlet.class.getName().equals(servlet.getClassName())) {
+                return true;
+            }
+        }
+        return false;
+    }
+
+    @Override
     public void addServletPackage(String servletPath, String restPackage) {
         throw new UnsupportedOperationException("addServletPackage()" + NOT_SUPPORTED);
     }