Validate server health ensuring print job are executed.

core/src/main/java/org/mapfish/print/metrics/ApplicationStatus.java

@@ -1,22 +1,59 @@
 package org.mapfish.print.metrics;
 
 import com.codahale.metrics.health.HealthCheck;
+import java.time.Instant;
+import java.time.temporal.TemporalAmount;
+import java.util.Date;
 import org.mapfish.print.servlet.job.JobQueue;
+import org.mapfish.print.servlet.job.impl.ThreadPoolJobManager;
 import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.beans.factory.annotation.Value;
 
 class ApplicationStatus extends HealthCheck {
-  public static final int MAX_WAITING_JOBS_TILL_UNHEALTHY = 5;
+  @Value("${expectedMaxTime.sinceLastPrint.InSeconds}")
+  private int SECONDS_IN_FLOATING_WINDOW;
+
+  private final TemporalAmount TIME_WINDOW_SIZE =
+      java.time.Duration.ofSeconds(SECONDS_IN_FLOATING_WINDOW);
   @Autowired private JobQueue jobQueue;
+  @Autowired private ThreadPoolJobManager jobManager;
+
+  private long previousNumberOfWaitingJobs = 0L;
 
   @Override
   protected Result check() throws Exception {
     long waitingJobsCount = jobQueue.getWaitingJobsCount();
-    String health = "Number of jobs waiting is " + waitingJobsCount;
+    if (waitingJobsCount == 0) {
+      previousNumberOfWaitingJobs = waitingJobsCount;
+      return Result.healthy("No print job is waiting in the queue.");
+    }
 
-    if (waitingJobsCount >= MAX_WAITING_JOBS_TILL_UNHEALTHY) {
-      return Result.unhealthy(health + ". It is too high.");
+    String health = "Number of print jobs waiting is " + waitingJobsCount;
+
+    if (jobManager.getLastExecutedJobTimestamp() == null) {
+      return Result.unhealthy("No print job was ever processed by this server. " + health);
+    } else if (jobManager
+        .getLastExecutedJobTimestamp()
+        .toInstant()
+        .isAfter(getBeginningOfTimeWindow())) {
+      if (waitingJobsCount > previousNumberOfWaitingJobs) {
+        previousNumberOfWaitingJobs = waitingJobsCount;
+        return Result.unhealthy(
+            "More print jobs are being queued. But this server is processing them. " + health);
+      } else {
+        previousNumberOfWaitingJobs = waitingJobsCount;
+        return Result.healthy(
+            "Print jobs are being dequeued. Number of print jobs waiting is " + waitingJobsCount);
+      }
     } else {
-      return Result.healthy(health);
+      previousNumberOfWaitingJobs = waitingJobsCount;
+      throw new RuntimeException(
+          "No print job was processed by this server, in the last (seconds): "
+              + SECONDS_IN_FLOATING_WINDOW);
     }
   }
+
+  private Instant getBeginningOfTimeWindow() {
+    return new Date().toInstant().minus(TIME_WINDOW_SIZE);
+  }
 }

core/src/main/java/org/mapfish/print/servlet/job/JobManager.java

@@ -1,8 +1,9 @@
 package org.mapfish.print.servlet.job;
 
+import java.util.Date;
+
 /** Manages and Executes Print Jobs. */
 public interface JobManager {
-
   /**
    * Submit a new job for execution.
    *
@@ -14,15 +15,22 @@ public interface JobManager {
    * Cancel a job.
    *
    * @param referenceId The referenceId of the job to cancel.
-   * @throws NoSuchReferenceException
+   * @throws NoSuchReferenceException When trying to cancel an unknown referenceId
    */
   void cancel(String referenceId) throws NoSuchReferenceException;
 
   /**
    * Get the status for a job.
    *
    * @param referenceId The referenceId of the job to check.
-   * @throws NoSuchReferenceException
+   * @throws NoSuchReferenceException When requesting status of an unknown referenceId
    */
   PrintJobStatus getStatus(String referenceId) throws NoSuchReferenceException;
+
+  /**
+   * Instant at which a job was executed by this manager
+   *
+   * @return the timestamp as a Date
+   */
+  Date getLastExecutedJobTimestamp();
 }

core/src/main/java/org/mapfish/print/servlet/job/impl/ThreadPoolJobManager.java

@@ -6,6 +6,7 @@
 import java.io.IOException;
 import java.util.Collections;
 import java.util.Comparator;
+import java.util.Date;
 import java.util.HashMap;
 import java.util.Iterator;
 import java.util.Map;
@@ -118,6 +119,7 @@ public class ThreadPoolJobManager implements JobManager {
   @Autowired private MetricRegistry metricRegistry;
 
   private boolean requestedToStop = false;
+  private Date lastExecutedJobTimestamp;
 
   public final void setMaxNumberOfRunningPrintJobs(final int maxNumberOfRunningPrintJobs) {
     this.maxNumberOfRunningPrintJobs = maxNumberOfRunningPrintJobs;
@@ -290,7 +292,12 @@ public final void shutdown() {
     }
   }
 
+  public Date getLastExecutedJobTimestamp() {
+    return lastExecutedJobTimestamp;
+  }
+
   private void executeJob(final PrintJob job) {
+    lastExecutedJobTimestamp = new Date();
     LOGGER.debug(
         "executeJob {}, PoolSize {}, CorePoolSize {}, Active {}, Completed {}, Task {}, isShutdown"
             + " {}, isTerminated {}",

core/src/main/resources/mapfish-spring.properties

@@ -52,3 +52,6 @@ httpRequest.fetchRetry.maxNumber=3
 
 # Number of milliseconds between 2 executions of the same request
 httpRequest.fetchRetry.intervalMillis=100
+
+# Amount of time in the past where we check if a print job was executed by this server
+expectedMaxTime.sinceLastPrint.InSeconds=300