Configurable retry delay and jitter

src/main/java/hudson/remoting/Engine.java

@@ -52,6 +52,7 @@
 import java.security.cert.CertificateException;
 import java.security.cert.X509Certificate;
 import java.security.interfaces.RSAPublicKey;
+import java.time.Duration;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Base64;
@@ -101,6 +102,7 @@
 import org.jenkinsci.remoting.protocol.cert.PublicKeyMatchingX509ExtendedTrustManager;
 import org.jenkinsci.remoting.protocol.impl.ConnectionRefusalException;
 import org.jenkinsci.remoting.util.KeyUtils;
+import org.jenkinsci.remoting.util.RetryUtils;
 import org.jenkinsci.remoting.util.VersionNumber;
 import org.jenkinsci.remoting.util.https.NoCheckHostnameVerifier;
 import org.jenkinsci.remoting.util.https.NoCheckTrustManager;
@@ -193,6 +195,12 @@ public Thread newThread(@NonNull final Runnable r) {
 
     private boolean noReconnect = false;
 
+    private int delay = 10;
+
+    private double jitterFactor = 0;
+
+    private int jitter = 0;
+
     /**
      * Determines whether the socket will have {@link Socket#setKeepAlive(boolean)} set or not.
      *
@@ -412,6 +420,21 @@ public void setNoReconnect(boolean noReconnect) {
         this.noReconnect = noReconnect;
     }
 
+    @Restricted(NoExternalUse.class)
+    public void setDelay(int delay) {
+        this.delay = delay;
+    }
+
+    @Restricted(NoExternalUse.class)
+    public void setJitterFactor(double jitterFactor) {
+        this.jitterFactor = jitterFactor;
+    }
+
+    @Restricted(NoExternalUse.class)
+    public void setJitter(int jitter) {
+        this.jitter = jitter;
+    }
+
     /**
      * Determines if JNLPAgentEndpointResolver will not perform certificate validation in the HTTPs mode.
      *
@@ -742,8 +765,8 @@ public void closeRead() throws IOException {
                 }
                 events.onDisconnect();
                 while (true) {
-                    // TODO refactor various sleep statements into a common method
-                    TimeUnit.SECONDS.sleep(10);
+                    Duration duration = RetryUtils.getDuration(delay, jitterFactor, jitter);
+                    Thread.sleep(duration.toMillis());
                     // Unlike JnlpAgentEndpointResolver, we do not use $jenkins/tcpSlaveAgentListener/, as that will be a 404 if the TCP port is disabled.
                     URL ping = new URL(hudsonUrl, "login");
                     try {
@@ -809,9 +832,9 @@ private void innerRun(IOHub hub, SSLContext context, ExecutorService service) {
                     endpoint = resolver.resolve();
                 } catch (IOException e) {
                     if (!noReconnect) {
-                        events.status("Could not locate server among " + candidateUrls + "; waiting 10 seconds before retry", e);
-                        // TODO refactor various sleep statements into a common method
-                        TimeUnit.SECONDS.sleep(10);
+                        Duration duration = RetryUtils.getDuration(delay, jitterFactor, jitter);
+                        events.status("Could not locate server among " + candidateUrls + "; waiting " + RetryUtils.formatDuration(duration) + " seconds before retry", e);
+                        Thread.sleep(duration.toMillis());
                         continue;
                     } else {
                         if (Boolean.getBoolean(Engine.class.getName() + ".nonFatalJnlpAgentEndpointResolutionExceptions")) {
@@ -929,26 +952,35 @@ private void innerRun(IOHub hub, SSLContext context, ExecutorService service) {
     }
 
     private JnlpEndpointResolver createEndpointResolver(List<String> jenkinsUrls, String agentName) {
-        JnlpEndpointResolver resolver;
         if (directConnection == null) {
             SSLSocketFactory sslSocketFactory = null;
             try {
                 sslSocketFactory = getSSLSocketFactory(candidateCertificates, disableHttpsCertValidation);
             } catch (Exception e) {
                 events.error(e);
             }
-            resolver = new JnlpAgentEndpointResolver(jenkinsUrls, agentName, credentials, proxyCredentials, tunnel,
-                    sslSocketFactory, disableHttpsCertValidation);
+            JnlpAgentEndpointResolver jnlpAgentEndpointResolver =
+                    new JnlpAgentEndpointResolver(
+                            jenkinsUrls,
+                            agentName,
+                            credentials,
+                            proxyCredentials,
+                            tunnel,
+                            sslSocketFactory,
+                            disableHttpsCertValidation);
+            jnlpAgentEndpointResolver.setDelay(delay);
+            jnlpAgentEndpointResolver.setJitterFactor(jitterFactor);
+            jnlpAgentEndpointResolver.setJitter(jitter);
+            return jnlpAgentEndpointResolver;
         } else {
-            resolver = new JnlpAgentEndpointConfigurator(directConnection, instanceIdentity, protocols, proxyCredentials);
+            return new JnlpAgentEndpointConfigurator(directConnection, instanceIdentity, protocols, proxyCredentials);
         }
-        return resolver;
     }
 
     private void onConnectionRejected(String greeting) throws InterruptedException {
-        events.status("reconnect rejected, sleeping 10s: ", new Exception("The server rejected the connection: " + greeting));
-        // TODO refactor various sleep statements into a common method
-        TimeUnit.SECONDS.sleep(10);
+        Duration duration = RetryUtils.getDuration(delay, jitterFactor, jitter);
+        events.status("reconnect rejected, sleeping " + RetryUtils.formatDuration(duration) + "s: ", new Exception("The server rejected the connection: " + greeting));
+        Thread.sleep(duration.toMillis());
     }
 
     /**
@@ -970,8 +1002,8 @@ private Socket connectTcp(@NonNull JnlpAgentEndpoint endpoint) throws IOExceptio
                 if(retry++>10) {
                     throw e;
                 }
-                // TODO refactor various sleep statements into a common method
-                TimeUnit.SECONDS.sleep(10);
+                Duration duration = RetryUtils.getDuration(delay, jitterFactor, jitter);
+                Thread.sleep(duration.toMillis());
                 events.status(msg+" (retrying:"+retry+")",e);
             }
         }

src/main/java/hudson/remoting/Launcher.java

@@ -30,6 +30,7 @@
 import org.jenkinsci.remoting.engine.JnlpAgentEndpointResolver;
 import org.jenkinsci.remoting.engine.WorkDirManager;
 import org.jenkinsci.remoting.util.PathUtils;
+import org.jenkinsci.remoting.util.RetryUtils;
 import org.jenkinsci.remoting.util.https.NoCheckHostnameVerifier;
 import org.kohsuke.args4j.Argument;
 import org.kohsuke.args4j.CmdLineException;
@@ -73,6 +74,7 @@
 import java.security.cert.CertificateException;
 import java.security.cert.CertificateFactory;
 import java.security.cert.X509Certificate;
+import java.time.Duration;
 import java.util.ArrayList;
 import java.util.HashSet;
 import java.util.List;
@@ -81,7 +83,6 @@
 import java.util.Properties;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
-import java.util.concurrent.TimeUnit;
 import java.util.logging.Level;
 import java.util.logging.Logger;
 
@@ -249,6 +250,25 @@
     @Option(name="-noReconnect",aliases="-noreconnect",usage="Doesn't try to reconnect when a communication fail, and exit instead")
     public boolean noReconnect = false;
 
+    @Option(name = "-retryDelay",
+            usage = "The fixed delay to occur between retries. Default is 10 seconds.")
+    public int delay = 10;
+
+    @Option(name = "-retryJitterFactor",
+            usage = "The jitter factor to randomly vary retry delays by. For each retry delay, a"
+                + " random portion of the delay multiplied by the jitter factor will be"
+                + " added or subtracted to the delay. For example: a retry delay of 10"
+                + " seconds and a jitter factor of .25 will result in a random retry delay"
+                + " between 7.5 and 12.5 seconds.")
+    public double jitterFactor = 0;
+
+    @Option(name = "-retryJitter",
+            usage = "The jitter to randomly vary retry delays by. For each retry delay, a random"
+                + " portion of the jitter will be added or subtracted to the delay. For"
+                + " example: a jitter of 5 seconds will randomly add between -5 and 5"
+                + " seconds to each retry delay.")
+    public int jitter = 0;
+
     @Option(name = "-noKeepAlive",
             usage = "Disable TCP socket keep alive on connection to the controller.")
     public boolean noKeepAlive = false;
@@ -450,8 +470,22 @@
         if (initialized) {
             throw new IllegalStateException("double initialization");
         }
+
+        if (jitterFactor != 0 && jitter != 0) {
+            throw new IllegalArgumentException("Jitter factor and jitter are mutually exclusive");
+        }
+        if (jitterFactor < 0 || jitterFactor > 1) {
+            throw new IllegalArgumentException("Jitter factor must be >= 0 and <= 1");
+        }
+        if (jitter < 0) {
+            throw new IllegalArgumentException("Jitter must be >= 0");
+        }
+        if (jitter > 0 && jitter >= delay) {
+            throw new IllegalArgumentException("Jitter must be < delay");
+        }
+
         // Create and verify working directory and logging
         // TODO: The pass-through for the JNLP mode has been added in JENKINS-39817. But we still need to keep this parameter in
         // consideration for other modes (TcpServer, TcpClient, etc.) to retain the legacy behavior.
         // On the other hand, in such case there is no need to invoke WorkDirManager and handle the double initialization logic
         final WorkDirManager workDirManager = WorkDirManager.getInstance();
@@ -745,9 +779,9 @@
 
                 System.err.println("Failed to obtain "+ agentJnlpURL);
                 e.printStackTrace(System.err);
-                System.err.println("Waiting 10 seconds before retry");
-                // TODO refactor various sleep statements into a common method
-                TimeUnit.SECONDS.sleep(10);
+                Duration duration = RetryUtils.getDuration(delay, jitterFactor, jitter);
+                System.err.println("Waiting " + RetryUtils.formatDuration(duration) + " seconds before retry");
+                Thread.sleep(duration.toMillis());
                 // retry
             } finally {
                 if (con instanceof HttpURLConnection) {

src/main/java/org/jenkinsci/remoting/engine/JnlpAgentEndpointResolver.java

@@ -29,6 +29,7 @@
 import hudson.remoting.Engine;
 import hudson.remoting.Launcher;
 import hudson.remoting.NoProxyEvaluator;
+import org.jenkinsci.remoting.util.RetryUtils;
 import org.jenkinsci.remoting.util.VersionNumber;
 import org.jenkinsci.remoting.util.https.NoCheckHostnameVerifier;
 import org.kohsuke.accmod.Restricted;
@@ -57,6 +58,7 @@
 import java.nio.charset.StandardCharsets;
 import java.security.interfaces.RSAPublicKey;
 import java.security.spec.InvalidKeySpecException;
+import java.time.Duration;
 import java.util.ArrayList;
 import java.util.Base64;
 import java.util.Iterator;
@@ -100,6 +102,12 @@ public class JnlpAgentEndpointResolver extends JnlpEndpointResolver {
 
     private HostnameVerifier hostnameVerifier;
 
+    private int delay = 10;
+
+    private double jitterFactor = 0;
+
+    private int jitter = 0;
+
     /**
      * If specified, only the protocols from the list will be tried during the connection.
      * The option provides protocol names, but the order of the check is defined internally and cannot be changed.
@@ -185,6 +193,21 @@ public void setDisableHttpsCertValidation(boolean disableHttpsCertValidation) {
         }
     }
 
+    @Restricted(NoExternalUse.class)
+    public void setDelay(int delay) {
+        this.delay = delay;
+    }
+
+    @Restricted(NoExternalUse.class)
+    public void setJitterFactor(double jitterFactor) {
+        this.jitterFactor = jitterFactor;
+    }
+
+    @Restricted(NoExternalUse.class)
+    public void setJitter(int jitter) {
+        this.jitter = jitter;
+    }
+
     @CheckForNull
     @Override
     public JnlpAgentEndpoint resolve() throws IOException {
@@ -402,8 +425,8 @@ public void waitForReady() throws InterruptedException {
         try {
             int retries = 0;
             while (true) {
-                // TODO refactor various sleep statements into a common method
-                Thread.sleep(1000 * 10);
+                Duration duration = RetryUtils.getDuration(delay, jitterFactor, jitter);
+                Thread.sleep(duration.toMillis());
                 // Jenkins top page might be read-protected. see http://www.nabble
                 // .com/more-lenient-retry-logic-in-Engine.waitForServerToBack-td24703172.html
                 if (jenkinsUrls.isEmpty()) {

src/main/java/org/jenkinsci/remoting/util/RetryUtils.java

@@ -0,0 +1,67 @@
+/*
+ * The MIT License
+ *
+ * Copyright (c) 2023, CloudBees, Inc.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package org.jenkinsci.remoting.util;
+
+import java.security.SecureRandom;
+import java.text.NumberFormat;
+import java.time.Duration;
+import java.util.Random;
+import org.kohsuke.accmod.Restricted;
+import org.kohsuke.accmod.restrictions.NoExternalUse;
+
+/**
+ * Retry-related utility methods. Used in place of a library like <a
+ * href="https://failsafe.dev/">Failsafe</a> to minimize external third-party dependencies.
+ */
+@Restricted(NoExternalUse.class)
+public class RetryUtils {
+
+    private static final Random RANDOM = new SecureRandom();
+
+    // Suppress default constructor for noninstantiability
+    private RetryUtils() {
+        throw new AssertionError();
+    }
+
+    /**
+     * Get the retry duration based on the CLI arguments.
+     */
+    public static Duration getDuration(int delay, double jitterFactor, int jitter) {
+        if (jitterFactor != 0) {
+            double randomFactor = 1 + (1 - RANDOM.nextDouble() * 2) * jitterFactor;
+            return Duration.ofMillis((long) (Duration.ofSeconds(delay).toMillis() * randomFactor));
+        } else if (jitter != 0) {
+            double randomAddend =
+                    (1 - RANDOM.nextDouble() * 2) * Duration.ofSeconds(jitter).toMillis();
+            return Duration.ofMillis((long) (Duration.ofSeconds(delay).toMillis() + randomAddend));
+        } else {
+            return Duration.ofSeconds(delay);
+        }
+    }
+
+    public static String formatDuration(Duration duration) {
+        return NumberFormat.getNumberInstance().format(duration.toMillis() / 1000.0);
+    }
+}