Update .NET 3.1 Agent to never upgrade to .NET 6 on unsupported OS

src/Agent.Listener/Agent.Listener.csproj

@@ -20,4 +20,10 @@
     <PackageReference Include="System.ServiceProcess.ServiceController" Version="4.4.0" />
     <PackageReference Include="vss-api-netcore" Version="$(VssApiVersion)" />
   </ItemGroup>
+
+  <ItemGroup>
+    <None Update="net6.json">
+      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
+    </None>
+  </ItemGroup>
 </Project>

src/Agent.Listener/SelfUpdater.cs

@@ -9,6 +9,7 @@
 using Microsoft.VisualStudio.Services.Agent.Util;
 using Microsoft.VisualStudio.Services.Common;
 using Microsoft.VisualStudio.Services.WebApi;
+using Newtonsoft.Json;
 using System;
 using System.Diagnostics;
 using System.IO;
@@ -147,6 +148,36 @@ private async Task<bool> UpdateNeeded(string targetVersion, CancellationToken to
             Trace.Info($"Current running agent version is {BuildConstants.AgentPackage.Version}");
             PackageVersion agentVersion = new PackageVersion(BuildConstants.AgentPackage.Version);
 
+            //Checking if current system support .NET 6 agent
+            if (agentVersion.Major == 2 && serverVersion.Major == 3)
+            {
+                Trace.Verbose("Checking if your system supports .NET 6");
+
+                try
+                {
+                    OS[] supportedSystems = GetSupportedSystemsNet6();
+
+                    string systemId = PlatformUtil.GetSystemId();
+                    OSVersion systemVersion = PlatformUtil.GetSystemVersion();
+
+                    Trace.Verbose($"The system you are running on: \"{systemId}\" ({systemVersion})");
+
+                    if (!supportedSystems.Any((system) => system.Equals(systemId, systemVersion)))
+                    {
+                        Trace.Warning($"The operating system the agent is running on is \"{systemId}\" ({systemVersion}), which will not be supported by the .NET 6 based v3 agent. Please upgrade the Operating System of this host to ensure compatibility with the v3 agent. See https://devblogs.microsoft.com/devops/upgrade-of-net-agent-for-azure-pipelines/");
+                        return false;
+                    }
+                    else
+                    {
+                        Trace.Verbose("The system persists in the list of systems supporting .NET 6");
+                    }
+                }
+                catch (Exception ex)
+                {
+                    Trace.Error($"Error has occurred while checking if system supports .NET 6: {ex} ");
+                }
+            }
+
             if (serverVersion.CompareTo(agentVersion) > 0)
             {
                 return true;
@@ -646,6 +677,18 @@ private bool VerifyAgentAuthenticode(string agentFolderPath)
 
             return true;
         }
+
+        private OS[] GetSupportedSystemsNet6()
+        {
+            string supportOSfilePath = Path.Combine(HostContext.GetDirectory(WellKnownDirectory.Bin), "net6.json");
+            if (!File.Exists(supportOSfilePath))
+            {
+                return Array.Empty<OS>();
+            }
+
+            string supportOSfileContent = File.ReadAllText(supportOSfilePath);
+            return JsonConvert.DeserializeObject<OS[]>(supportOSfileContent)!;
+        }
     }
 
     public class UpdaterKnobValueContext : IKnobValueContext
@@ -660,4 +703,28 @@ public IScopedEnvironment GetScopedEnvironment()
             return new SystemEnvironment();
         }
     }
+
+    public class OS
+    {
+        public string Id { get; set; }
+
+        public OSVersion[] Versions { get; set; }
+
+        public OS() { }
+
+        public bool Equals(string systemId, OSVersion systemVersion)
+        {
+            if (!this.Id.Equals(systemId, StringComparison.OrdinalIgnoreCase))
+            {
+                return false;
+            }
+
+            if (this.Versions.Length == 0)
+            {
+                return false;
+            }
+
+            return this.Versions.Any(version => version.Equals(systemVersion));
+        }
+    }
 }

src/Agent.Listener/net6.json

@@ -0,0 +1,129 @@
+[
+  {
+    "id": "alpine",
+    "versions": [
+      {
+        "name": "3.13+"
+      }
+    ]
+  },
+  {
+    "id": "amzn",
+    "versions": [
+      {
+        "name": "2"
+      }
+    ]
+  },
+  {
+    "id": "centos",
+    "versions": [
+      {
+        "name": "7+"
+      }
+    ]
+  },
+  {
+    "id": "debian",
+    "versions": [
+      {
+        "name": "10+"
+      }
+    ]
+  },
+  {
+    "id": "fedora",
+    "versions": [
+      {
+        "name": "33+"
+      }
+    ]
+  },
+  {
+    "id": "macOS",
+    "versions": [
+      {
+        "name": "10.15+"
+      }
+    ]
+  },
+  {
+    "id": "opensuse-leap",
+    "versions": [
+      {
+        "name": "15+"
+      }
+    ]
+  },
+  {
+    "id": "rhel",
+    "versions": [
+      {
+        "name": "7+"
+      }
+    ]
+  },
+  {
+    "id": "sles",
+    "versions": [
+      {
+        "name": "12.2+"
+      }
+    ]
+  },
+  {
+    "id": "ubuntu",
+    "versions": [
+      {
+        "name": "16.04"
+      },
+      {
+        "name": "18.04"
+      },
+      {
+        "name": "20.04+"
+      }
+
+    ]
+  },
+  {
+    "id": "Windows Client",
+    "versions": [
+      {
+        "name": "7",
+        "version": "7601+"
+      },
+      {
+        "name": "8.1"
+      },
+      {
+        "name": "10",
+        "version": "14393+"
+      }
+    ]
+  },
+  {
+    "id": "Windows Nano Server",
+    "versions": [
+      {
+        "version": "17763+"
+      }
+    ]
+  },
+  {
+    "id": "Windows Server",
+    "versions": [
+      {
+        "name": "2012+"
+      }
+    ]
+  },
+  {
+    "id": "Windows Server Core",
+    "versions": [
+      {
+        "name": "2012+"
+      }
+    ]
+  }
+]