add health/ready endpoints

Signed-off-by: John Izaak Alpert <ialpert@salesforce.com>

src/main/java/io/prometheus/cloudwatch/HealthServlet.java

@@ -0,0 +1,15 @@
+package io.prometheus.cloudwatch;
+
+import javax.servlet.ServletException;
+import javax.servlet.http.HttpServlet;
+import javax.servlet.http.HttpServletRequest;
+import javax.servlet.http.HttpServletResponse;
+import java.io.IOException;
+
+public class HealthServlet extends HttpServlet {
+
+    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
+        resp.setContentType("text/html");
+        resp.getWriter().print("OK");
+    }
+}

src/main/java/io/prometheus/cloudwatch/WebServer.java

@@ -33,6 +33,8 @@ public static void main(String[] args) throws Exception {
         server.setHandler(context);
         context.addServlet(new ServletHolder(new MetricsServlet()), "/metrics");
         context.addServlet(new ServletHolder(new DynamicReloadServlet(collector)), "/-/reload");
+        context.addServlet(new ServletHolder(new HealthServlet()), "/-/healthy");
+        context.addServlet(new ServletHolder(new HealthServlet()), "/-/ready");
         context.addServlet(new ServletHolder(new HomePageServlet()), "/");
         server.start();
         server.join();