Add unified Node.js version selection strategy framework with EOL policy support

src/Agent.Sdk/Knob/AgentKnobs.cs

@@ -568,6 +568,13 @@ public class AgentKnobs
             new EnvironmentKnobSource("AGENT_DISABLE_NODE6_TASKS"),
             new BuiltInDefaultKnobSource("false"));
 
+        public static readonly Knob EnableEOLNodeVersionPolicy = new Knob(
+            nameof(EnableEOLNodeVersionPolicy),
+            "When enabled, automatically upgrades tasks using end-of-life Node.js versions (6, 10, 16) to supported versions (Node 20.1 or Node 24). Throws error if no supported versions are available on the agent.",
+            new PipelineFeatureSource("AGENT_RESTRICT_EOL_NODE_VERSIONS"),
+            new EnvironmentKnobSource("AGENT_RESTRICT_EOL_NODE_VERSIONS"),
+            new BuiltInDefaultKnobSource("false"));
+
         public static readonly Knob DisableTeePluginRemoval = new Knob(
             nameof(DisableTeePluginRemoval),
             "Disables removing TEE plugin after using it during checkout.",

src/Agent.Worker/NodeVersionStrategies/IUnifiedNodeVersionStrategy.cs

@@ -0,0 +1,37 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+
+using System;
+
+namespace Microsoft.VisualStudio.Services.Agent.Worker.NodeVersionStrategies
+{
+    /// <summary>
+    /// Strategy interface for both host and container node selection.
+    /// </summary>
+    public interface IUnifiedNodeVersionStrategy
+    {
+        /// <summary>
+        /// Human-readable name of this strategy for logging and debugging.
+        /// Examples: "Node24", "Node20", "Node16", "CustomNode"
+        /// </summary>
+        string Name { get; }
+
+        /// <summary>
+        /// Checks if this strategy can handle the given context.
+        /// Includes handler type, knob checks, EOL policy, and glibc compatibility.
+        /// </summary>
+        /// <param name="context">Context with environment, task, and glibc information</param>
+        /// <returns>True if this strategy can handle the context, false otherwise</returns>
+        bool CanHandle(UnifiedNodeContext context);
+
+        /// <summary>
+        /// Gets the Node path for the given context.
+        /// Works for both host and container (path translation handled internally).
+        /// May throw NotSupportedException if EOL policy is violated.
+        /// </summary>
+        /// <param name="context">Context with environment, task, and glibc information</param>
+        /// <returns>NodePathResult with path, version, reason, and optional warning</returns>
+        /// <exception cref="NotSupportedException">If EOL policy prevents using this version</exception>
+        NodePathResult GetNodePath(UnifiedNodeContext context);
+    }
+}

src/Agent.Worker/NodeVersionStrategies/NodePathResult.cs

@@ -0,0 +1,36 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+
+using System;
+
+namespace Microsoft.VisualStudio.Services.Agent.Worker.NodeVersionStrategies
+{
+    /// <summary>
+    /// Result containing the selected Node path and metadata.
+    /// Used by unified strategy pattern for both host and container node selection.
+    /// </summary>
+    public sealed class NodePathResult
+    {
+        /// <summary>
+        /// Full path to the node executable.
+        /// </summary>
+        public string NodePath { get; set; }
+
+        /// <summary>
+        /// The node version folder name (e.g., "node24", "node20_1", "node16").
+        /// </summary>
+        public string NodeVersion { get; set; }
+
+        /// <summary>
+        /// Explanation of why this version was selected.
+        /// Used for debugging and telemetry.
+        /// </summary>
+        public string Reason { get; set; }
+
+        /// <summary>
+        /// Optional warning message to display to user.
+        /// Example: "Container OS doesn't support Node24, using Node20 instead."
+        /// </summary>
+        public string Warning { get; set; }
+    }
+}

src/Agent.Worker/NodeVersionStrategies/UnifiedNode10Strategy.cs

@@ -0,0 +1,69 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+
+using System;
+using System.IO;
+using Agent.Sdk.Knob;
+using Microsoft.TeamFoundation.DistributedTask.WebApi;
+using Microsoft.VisualStudio.Services.Agent.Util;
+using Microsoft.VisualStudio.Services.Agent.Worker;
+
+namespace Microsoft.VisualStudio.Services.Agent.Worker.NodeVersionStrategies
+{
+    public sealed class UnifiedNode10Strategy : IUnifiedNodeVersionStrategy
+    {
+        public string Name => "Node10";
+
+        public bool CanHandle(UnifiedNodeContext context)
+        {
+            bool hasNode10Handler = context.HandlerData is Node10HandlerData;
+            bool eolPolicyEnabled = AgentKnobs.EnableEOLNodeVersionPolicy.GetValue(context.ExecutionContext).AsBoolean();
+
+            if (hasNode10Handler)
+            {
+                return DetermineNodeVersionAndSetContext(context, eolPolicyEnabled, "Selected for Node10 task handler");
+            }
+
+            bool isAlpine = context.IsAlpine;
+            if (isAlpine)
+            {
+                context.ExecutionContext.Warning(
+                    "Using Node10 on Alpine Linux because Node6 is not compatible. " +
+                    "Node10 has reached End-of-Life. Please upgrade to Node20 or Node24 for continued support.");
+
+                return DetermineNodeVersionAndSetContext(context, eolPolicyEnabled, "Selected for Alpine Linux compatibility (Node6 incompatible)");
+            }
+
+            return false;
+        }
+
+        private bool DetermineNodeVersionAndSetContext(UnifiedNodeContext context, bool eolPolicyEnabled, string baseReason)
+        {
+            if (eolPolicyEnabled)
+            {
+                throw new NotSupportedException(StringUtil.Loc("NodeEOLPolicyBlocked", "Node10"));
+            }
+
+            context.SelectedNodeVersion = "node10";
+            context.SelectionReason = baseReason;
+            context.SelectionWarning = StringUtil.Loc("NodeEOLWarning", "Node10");
+            return true;
+        }
+
+        public NodePathResult GetNodePath(UnifiedNodeContext context)
+        {
+            string externalsPath = context.HostContext.GetDirectory(WellKnownDirectory.Externals);
+            string hostPath = Path.Combine(externalsPath, context.SelectedNodeVersion, "bin", $"node{IOUtil.ExeExtension}");
+            string finalPath = context.IsContainer && context.Container != null ? 
+                              context.Container.TranslateToContainerPath(hostPath) : hostPath;
+
+            return new NodePathResult
+            {
+                NodePath = finalPath,
+                NodeVersion = context.SelectedNodeVersion,
+                Reason = context.SelectionReason,
+                Warning = context.SelectionWarning
+            };
+        }
+    }
+}

src/Agent.Worker/NodeVersionStrategies/UnifiedNode16Strategy.cs

@@ -0,0 +1,59 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+
+using System;
+using System.IO;
+using Agent.Sdk.Knob;
+using Microsoft.TeamFoundation.DistributedTask.WebApi;
+using Microsoft.VisualStudio.Services.Agent.Util;
+using Microsoft.VisualStudio.Services.Agent.Worker;
+
+namespace Microsoft.VisualStudio.Services.Agent.Worker.NodeVersionStrategies
+{
+    public sealed class UnifiedNode16Strategy : IUnifiedNodeVersionStrategy
+    {
+        public string Name => "Node16";
+
+        public bool CanHandle(UnifiedNodeContext context)
+        {
+            bool hasNode16Handler = context.HandlerData is Node16HandlerData;
+            bool eolPolicyEnabled = AgentKnobs.EnableEOLNodeVersionPolicy.GetValue(context.ExecutionContext).AsBoolean();
+
+            if (hasNode16Handler)
+            {
+                return DetermineNodeVersionAndSetContext(context, eolPolicyEnabled, "Selected for Node16 task handler");
+            }
+
+            return false;
+        }
+
+        private bool DetermineNodeVersionAndSetContext(UnifiedNodeContext context, bool eolPolicyEnabled, string baseReason)
+        {
+            if (eolPolicyEnabled)
+            {
+                throw new NotSupportedException(StringUtil.Loc("NodeEOLPolicyBlocked", "Node16"));
+            }
+
+            context.SelectedNodeVersion = "node16";
+            context.SelectionReason = baseReason;
+            context.SelectionWarning = StringUtil.Loc("NodeEOLWarning", "Node16");
+            return true;
+        }
+
+        public NodePathResult GetNodePath(UnifiedNodeContext context)
+        {
+            string externalsPath = context.HostContext.GetDirectory(WellKnownDirectory.Externals);
+            string hostPath = Path.Combine(externalsPath, context.SelectedNodeVersion, "bin", $"node{IOUtil.ExeExtension}");
+            string finalPath = context.IsContainer && context.Container != null ? 
+                              context.Container.TranslateToContainerPath(hostPath) : hostPath;
+
+            return new NodePathResult
+            {
+                NodePath = finalPath,
+                NodeVersion = context.SelectedNodeVersion,
+                Reason = context.SelectionReason,
+                Warning = context.SelectionWarning
+            };
+        }
+    }
+}

src/Agent.Worker/NodeVersionStrategies/UnifiedNode20Strategy.cs

@@ -0,0 +1,79 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+
+using System;
+using System.IO;
+using Agent.Sdk.Knob;
+using Microsoft.TeamFoundation.DistributedTask.WebApi;
+using Microsoft.VisualStudio.Services.Agent.Util;
+using Microsoft.VisualStudio.Services.Agent.Worker;
+
+namespace Microsoft.VisualStudio.Services.Agent.Worker.NodeVersionStrategies
+{
+    public sealed class UnifiedNode20Strategy : IUnifiedNodeVersionStrategy
+    {
+        public string Name => "Node20";
+
+        public bool CanHandle(UnifiedNodeContext context)
+        {
+            bool useNode20Globally = AgentKnobs.UseNode20_1.GetValue(context.ExecutionContext).AsBoolean();
+            bool hasNode20Handler = context.HandlerData is Node20_1HandlerData;
+            bool eolPolicyEnabled = AgentKnobs.EnableEOLNodeVersionPolicy.GetValue(context.ExecutionContext).AsBoolean();
+
+            if (useNode20Globally)
+            {
+                return DetermineNodeVersionAndSetContext(context, eolPolicyEnabled, "Selected via global AGENT_USE_NODE20_1 override");
+            }
+
+            if (hasNode20Handler)
+            {
+                return DetermineNodeVersionAndSetContext(context, eolPolicyEnabled, "Selected for Node20 task handler");
+            }
+
+            if (eolPolicyEnabled)
+            {
+                return DetermineNodeVersionAndSetContext(context, eolPolicyEnabled, "Upgraded from end-of-life Node version due to EOL policy");
+            }
+
+            return false;
+        }
+
+        private bool DetermineNodeVersionAndSetContext(UnifiedNodeContext context, bool eolPolicyEnabled, string baseReason)
+        {
+            if (!context.Node20HasGlibcError)
+            {
+                context.SelectedNodeVersion = "node20_1";
+                context.SelectionReason = baseReason;
+                context.SelectionWarning = null;
+                return true;
+            }
+
+            if (eolPolicyEnabled)
+            {
+                throw new NotSupportedException(StringUtil.Loc("NodeEOLFallbackBlocked", "Node20", "Node16"));
+            }
+
+            string systemType = context.IsContainer ? "container" : "agent";
+            context.SelectedNodeVersion = "node16";
+            context.SelectionReason = $"{baseReason}, fallback to Node16 due to Node20 glibc compatibility issue";
+            context.SelectionWarning = StringUtil.Loc("NodeGlibcFallbackWarning", systemType, "Node20", "Node16");
+            return true;
+        }
+
+        public NodePathResult GetNodePath(UnifiedNodeContext context)
+        {
+            string externalsPath = context.HostContext.GetDirectory(WellKnownDirectory.Externals);
+            string hostPath = Path.Combine(externalsPath, context.SelectedNodeVersion, "bin", $"node{IOUtil.ExeExtension}");
+            string finalPath = context.IsContainer && context.Container != null ? 
+                              context.Container.TranslateToContainerPath(hostPath) : hostPath;
+
+            return new NodePathResult
+            {
+                NodePath = finalPath,
+                NodeVersion = context.SelectedNodeVersion,
+                Reason = context.SelectionReason,
+                Warning = context.SelectionWarning
+            };
+        }
+    }
+}