Fix not setting the Server Software field when editing an instance

Server/Phantom.Server.Database/Enums/AuditEventType.cs

@@ -11,6 +11,7 @@ public enum AuditEventType {
 	UserRolesChanged,
 	UserDeleted,
 	InstanceCreated,
+	InstanceEdited,
 	InstanceLaunched,
 	InstanceStopped,
 	InstanceCommandExecuted
@@ -26,6 +27,7 @@ public static partial class AuditEventCategoryExtensions {
 		{ AuditEventType.UserRolesChanged,          AuditSubjectType.User },
 		{ AuditEventType.UserDeleted,               AuditSubjectType.User },
 		{ AuditEventType.InstanceCreated,           AuditSubjectType.Instance },
+		{ AuditEventType.InstanceEdited,            AuditSubjectType.Instance },
 		{ AuditEventType.InstanceLaunched,          AuditSubjectType.Instance },
 		{ AuditEventType.InstanceStopped,           AuditSubjectType.Instance },
 		{ AuditEventType.InstanceCommandExecuted,   AuditSubjectType.Instance }

Server/Phantom.Server.Services/Agents/Agent.cs

@@ -24,6 +24,11 @@ public sealed record Agent(
 	
 	internal Agent(AgentInfo info) : this(info.Guid, info.Name, info.ProtocolVersion, info.BuildVersion, info.MaxInstances, info.MaxMemory, info.AllowedServerPorts, info.AllowedRconPorts) {}
 
+	internal Agent AsOnline(DateTimeOffset lastPing) => this with {
+		LastPing = lastPing,
+		IsOnline = Connection != null
+	};
+	
 	internal Agent AsDisconnected() => this with {
 		IsOnline = false
 	};

Server/Phantom.Server.Services/Agents/AgentManager.cs

@@ -101,7 +101,7 @@ public sealed class AgentManager {
 	}
 
 	internal void NotifyAgentIsAlive(Guid agentGuid) {
-		agents.ByGuid.TryReplace(agentGuid, static agent => agent with { LastPing = DateTimeOffset.Now });
+		agents.ByGuid.TryReplace(agentGuid, static agent => agent.AsOnline(DateTimeOffset.Now));
 	}
 
 	internal void SetAgentStats(Guid agentGuid, int runningInstanceCount, RamAllocationUnits runningInstanceMemory) {

Server/Phantom.Server.Services/Audit/AuditLog.EventTypes.cs

@@ -50,6 +50,10 @@ public sealed partial class AuditLog {
 		return AddEvent(AuditEventType.InstanceCreated, instanceGuid.ToString());
 	}
 
+	public Task AddInstanceEditedEvent(Guid instanceGuid) {
+		return AddEvent(AuditEventType.InstanceEdited, instanceGuid.ToString());
+	}
+	
 	public Task AddInstanceLaunchedEvent(Guid instanceGuid) {
 		return AddEvent(AuditEventType.InstanceLaunched, instanceGuid.ToString());
 	}

Server/Phantom.Server.Services/Instances/AddInstanceResult.cs

@@ -1,22 +0,0 @@
-namespace Phantom.Server.Services.Instances;
-
-public enum AddInstanceResult : byte {
-	UnknownError,
-	Success,
-	InstanceAlreadyExists,
-	InstanceNameMustNotBeEmpty,
-	InstanceMemoryMustNotBeZero,
-	AgentNotFound
-}
-
-public static class AddInstanceResultExtensions {
-	public static string ToSentence(this AddInstanceResult reason) {
-		return reason switch {
-			AddInstanceResult.Success                     => "Success.",
-			AddInstanceResult.InstanceNameMustNotBeEmpty  => "Instance name must not be empty.",
-			AddInstanceResult.InstanceMemoryMustNotBeZero => "Memory must not be 0 MB.",
-			AddInstanceResult.AgentNotFound               => "Agent not found.",
-			_                                             => "Unknown error."
-		};
-	}
-}

Server/Phantom.Server.Services/Instances/AddOrEditInstanceResult.cs

@@ -0,0 +1,21 @@
+namespace Phantom.Server.Services.Instances;
+
+public enum AddOrEditInstanceResult : byte {
+	UnknownError,
+	Success,
+	InstanceNameMustNotBeEmpty,
+	InstanceMemoryMustNotBeZero,
+	AgentNotFound
+}
+
+public static class AddOrEditInstanceResultExtensions {
+	public static string ToSentence(this AddOrEditInstanceResult reason) {
+		return reason switch {
+			AddOrEditInstanceResult.Success                     => "Success.",
+			AddOrEditInstanceResult.InstanceNameMustNotBeEmpty  => "Instance name must not be empty.",
+			AddOrEditInstanceResult.InstanceMemoryMustNotBeZero => "Memory must not be 0 MB.",
+			AddOrEditInstanceResult.AgentNotFound               => "Agent not found.",
+			_                                                   => "Unknown error."
+		};
+	}
+}

Server/Phantom.Server.Services/Instances/InstanceManager.cs

@@ -1,4 +1,6 @@
 using System.Collections.Immutable;
+using System.Diagnostics.CodeAnalysis;
+using Phantom.Common.Data;
 using Phantom.Common.Data.Instance;
 using Phantom.Common.Data.Minecraft;
 using Phantom.Common.Data.Replies;
@@ -25,6 +27,7 @@ public sealed class InstanceManager {
 	private readonly CancellationToken cancellationToken;
 	private readonly AgentManager agentManager;
 	private readonly DatabaseProvider databaseProvider;
+	private readonly SemaphoreSlim modifyInstancesSemaphore = new (1, 1);
 
 	public InstanceManager(ServiceConfiguration configuration, AgentManager agentManager, DatabaseProvider databaseProvider) {
 		this.cancellationToken = configuration.CancellationToken;
@@ -55,27 +58,40 @@ public sealed class InstanceManager {
 		}
 	}
 
-	public async Task<InstanceActionResult<AddInstanceResult>> AddInstance(InstanceConfiguration configuration) {
+	[SuppressMessage("ReSharper", "ConvertIfStatementToConditionalTernaryExpression")]
+	public async Task<InstanceActionResult<AddOrEditInstanceResult>> AddOrEditInstance(InstanceConfiguration configuration) {
 		var agent = agentManager.GetAgent(configuration.AgentGuid);
 		if (agent == null) {
-			return InstanceActionResult.Concrete(AddInstanceResult.AgentNotFound);
+			return InstanceActionResult.Concrete(AddOrEditInstanceResult.AgentNotFound);
 		}
 
-		var instance = new Instance(configuration);
-		if (!instances.ByGuid.TryAdd(instance.Configuration.InstanceGuid, instance)) {
-			return InstanceActionResult.Concrete(AddInstanceResult.InstanceAlreadyExists);
+		if (string.IsNullOrWhiteSpace(configuration.InstanceName)) {
+			return InstanceActionResult.Concrete(AddOrEditInstanceResult.InstanceNameMustNotBeEmpty);
 		}
-
-		var agentName = agent.Name;
-
-		var reply = await agentManager.SendMessage<ConfigureInstanceMessage, InstanceActionResult<ConfigureInstanceResult>>(configuration.AgentGuid, new ConfigureInstanceMessage(configuration), TimeSpan.FromSeconds(10));
-		var result = reply.DidNotReplyIfNull().Map(static result => result switch {
-			ConfigureInstanceResult.Success => AddInstanceResult.Success,
-			_                               => AddInstanceResult.UnknownError
-		});
 		
-		if (result.Is(AddInstanceResult.Success)) {
-			using (var scope = databaseProvider.CreateScope()) {
+		if (configuration.MemoryAllocation <= RamAllocationUnits.Zero) {
+			return InstanceActionResult.Concrete(AddOrEditInstanceResult.InstanceMemoryMustNotBeZero);
+		}
+		
+		InstanceActionResult<AddOrEditInstanceResult> result;
+		bool isNewInstance;
+
+		await modifyInstancesSemaphore.WaitAsync(cancellationToken);
+		try {
+			var instance = new Instance(configuration);
+			instances.ByGuid.AddOrReplace(instance.Configuration.InstanceGuid, instance, out var oldInstance);
+			
+			var reply = await agentManager.SendMessage<ConfigureInstanceMessage, InstanceActionResult<ConfigureInstanceResult>>(configuration.AgentGuid, new ConfigureInstanceMessage(configuration), TimeSpan.FromSeconds(10));
+			
+			result = reply.DidNotReplyIfNull().Map(static result => result switch {
+				ConfigureInstanceResult.Success => AddOrEditInstanceResult.Success,
+				_                               => AddOrEditInstanceResult.UnknownError
+			});
+
+			isNewInstance = oldInstance == null;
+			
+			if (result.Is(AddOrEditInstanceResult.Success)) {
+				using var scope = databaseProvider.CreateScope();
 				InstanceEntity entity = scope.Ctx.InstanceUpsert.Fetch(configuration.InstanceGuid);
 
 				entity.AgentGuid = configuration.AgentGuid;
@@ -91,14 +107,30 @@ public sealed class InstanceManager {
 
 				await scope.Ctx.SaveChangesAsync(cancellationToken);
 			}
-
-			Logger.Information("Added instance \"{InstanceName}\" (GUID {InstanceGuid}) to agent \"{AgentName}\".", configuration.InstanceName, configuration.InstanceGuid, agentName);
-		}
-		else {
-			instances.ByGuid.Remove(configuration.InstanceGuid);
-			Logger.Information("Failed adding instance \"{InstanceName}\" (GUID {InstanceGuid}) to agent \"{AgentName}\". {ErrorMessage}", configuration.InstanceName, configuration.InstanceGuid, agentName, result.ToSentence(AddInstanceResultExtensions.ToSentence));
+			else if (isNewInstance) {
+				instances.ByGuid.Remove(configuration.InstanceGuid);
+			}
+		} finally {
+			modifyInstancesSemaphore.Release();
 		}
 		
+		if (result.Is(AddOrEditInstanceResult.Success)) {
+			if (isNewInstance) {
+				Logger.Information("Added instance \"{InstanceName}\" (GUID {InstanceGuid}) to agent \"{AgentName}\".", configuration.InstanceName, configuration.InstanceGuid, agent.Name);
+			}
+			else {
+				Logger.Information("Edited instance \"{InstanceName}\" (GUID {InstanceGuid}) in agent \"{AgentName}\".", configuration.InstanceName, configuration.InstanceGuid, agent.Name);
+			}
+		}
+		else {
+			if (isNewInstance) {
+				Logger.Information("Failed adding instance \"{InstanceName}\" (GUID {InstanceGuid}) to agent \"{AgentName}\". {ErrorMessage}", configuration.InstanceName, configuration.InstanceGuid, agent.Name, result.ToSentence(AddOrEditInstanceResultExtensions.ToSentence));
+			}
+			else {
+				Logger.Information("Failed editing instance \"{InstanceName}\" (GUID {InstanceGuid}) in agent \"{AgentName}\". {ErrorMessage}", configuration.InstanceName, configuration.InstanceGuid, agent.Name, result.ToSentence(AddOrEditInstanceResultExtensions.ToSentence));
+			}
+		}
+
 		return result;
 	}
 
@@ -106,8 +138,8 @@ public sealed class InstanceManager {
 		return instances.ByGuid.ToImmutable<string>(static instance => instance.Configuration.InstanceName);
 	}
 
-	private Instance? GetInstance(Guid instanceGuid) {
-		return instances.ByGuid.TryGetValue(instanceGuid, out var instance) ? instance : null;
+	public InstanceConfiguration? GetInstanceConfiguration(Guid instanceGuid) {
+		return instances.ByGuid.TryGetValue(instanceGuid, out var instance) ? instance.Configuration : null;
 	}
 
 	internal void SetInstanceState(Guid instanceGuid, IInstanceStatus instanceStatus) {
@@ -123,48 +155,48 @@ public sealed class InstanceManager {
 		return reply.DidNotReplyIfNull();
 	}
 
+	private async Task<InstanceActionResult<TReply>> SendInstanceActionMessage<TMessage, TReply>(Guid instanceGuid, TMessage message) where TMessage : IMessageToAgent<InstanceActionResult<TReply>> {
+		return instances.ByGuid.TryGetValue(instanceGuid, out var instance) ? await SendInstanceActionMessage<TMessage, TReply>(instance, message) : InstanceActionResult.General<TReply>(InstanceActionGeneralResult.InstanceDoesNotExist);
+	}
+
 	public async Task<InstanceActionResult<LaunchInstanceResult>> LaunchInstance(Guid instanceGuid) {
-		var instance = GetInstance(instanceGuid);
-		if (instance == null) {
-			return InstanceActionResult.General<LaunchInstanceResult>(InstanceActionGeneralResult.InstanceDoesNotExist);
+		var result = await SendInstanceActionMessage<LaunchInstanceMessage, LaunchInstanceResult>(instanceGuid, new LaunchInstanceMessage(instanceGuid));
+		if (result.Is(LaunchInstanceResult.LaunchInitiated)) {
+			await SetInstanceShouldLaunchAutomatically(instanceGuid, true);
 		}
 
-		await SetInstanceShouldLaunchAutomatically(instanceGuid, true);
-
-		return await SendInstanceActionMessage<LaunchInstanceMessage, LaunchInstanceResult>(instance, new LaunchInstanceMessage(instanceGuid));
+		return result;
 	}
 
 	public async Task<InstanceActionResult<StopInstanceResult>> StopInstance(Guid instanceGuid, MinecraftStopStrategy stopStrategy) {
-		var instance = GetInstance(instanceGuid);
-		if (instance == null) {
-			return InstanceActionResult.General<StopInstanceResult>(InstanceActionGeneralResult.InstanceDoesNotExist);
+		var result = await SendInstanceActionMessage<StopInstanceMessage, StopInstanceResult>(instanceGuid, new StopInstanceMessage(instanceGuid, stopStrategy));
+		if (result.Is(StopInstanceResult.StopInitiated)) {
+			await SetInstanceShouldLaunchAutomatically(instanceGuid, false);
 		}
 
-		await SetInstanceShouldLaunchAutomatically(instanceGuid, false);
-
-		return await SendInstanceActionMessage<StopInstanceMessage, StopInstanceResult>(instance, new StopInstanceMessage(instanceGuid, stopStrategy));
+		return result;
 	}
 
 	private async Task SetInstanceShouldLaunchAutomatically(Guid instanceGuid, bool shouldLaunchAutomatically) {
-		instances.ByGuid.TryReplace(instanceGuid, instance => instance with {
-			Configuration = instance.Configuration with { LaunchAutomatically = shouldLaunchAutomatically }
-		});
+		await modifyInstancesSemaphore.WaitAsync(cancellationToken);
+		try {
+			instances.ByGuid.TryReplace(instanceGuid, instance => instance with {
+				Configuration = instance.Configuration with { LaunchAutomatically = shouldLaunchAutomatically }
+			});
 
-		using var scope = databaseProvider.CreateScope();
-		var entity = await scope.Ctx.Instances.FindAsync(instanceGuid, cancellationToken);
-		if (entity != null) {
-			entity.LaunchAutomatically = shouldLaunchAutomatically;
-			await scope.Ctx.SaveChangesAsync(cancellationToken);
+			using var scope = databaseProvider.CreateScope();
+			var entity = await scope.Ctx.Instances.FindAsync(instanceGuid, cancellationToken);
+			if (entity != null) {
+				entity.LaunchAutomatically = shouldLaunchAutomatically;
+				await scope.Ctx.SaveChangesAsync(cancellationToken);
+			}
+		} finally {
+			modifyInstancesSemaphore.Release();
 		}
 	}
 
 	public async Task<InstanceActionResult<SendCommandToInstanceResult>> SendCommand(Guid instanceGuid, string command) {
-		var instance = GetInstance(instanceGuid);
-		if (instance == null) {
-			return InstanceActionResult.General<SendCommandToInstanceResult>(InstanceActionGeneralResult.InstanceDoesNotExist);
-		}
-
-		return await SendInstanceActionMessage<SendCommandToInstanceMessage, SendCommandToInstanceResult>(instance, new SendCommandToInstanceMessage(instanceGuid, command));
+		return await SendInstanceActionMessage<SendCommandToInstanceMessage, SendCommandToInstanceResult>(instanceGuid, new SendCommandToInstanceMessage(instanceGuid, command));
 	}
 
 	internal ImmutableArray<InstanceConfiguration> GetInstanceConfigurationsForAgent(Guid agentGuid) {

Server/Phantom.Server.Web/Pages/Agents.razor

@@ -13,7 +13,7 @@
       <Column Width=" 90px; 19%" Class="text-end">Instances</Column>
       <Column Width="145px; 21%" Class="text-end">Memory</Column>
       <Column Width="180px;  8%">Version</Column>
-      <Column Width="315px">Identifier</Column>
+      <Column Width="320px">Identifier</Column>
       <Column Width="100px;  8%" Class="text-center">Status</Column>
       <Column Width="215px" Class="text-end">Last Ping</Column>
     </tr>

Server/Phantom.Server.Web/Pages/InstanceCreate.razor

@@ -1,304 +1,5 @@
 @page "/instances/create"
-@using Phantom.Common.Data.Minecraft
-@using Phantom.Common.Minecraft
-@using Phantom.Server.Services.Agents
-@using Phantom.Server.Services.Audit
-@using Phantom.Server.Services.Instances
-@using System.Collections.Immutable
-@using System.ComponentModel.DataAnnotations
-@using System.Diagnostics.CodeAnalysis
-@using Phantom.Server.Web.Components.Utils
-@using Phantom.Server.Web.Identity.Interfaces
-@using Phantom.Common.Data.Java
-@using Phantom.Common.Data
-@using Phantom.Common.Data.Instance
 @attribute [Authorize(Permission.CreateInstancesPolicy)]
-@inject INavigation Nav
-@inject MinecraftVersions MinecraftVersions
-@inject AgentManager AgentManager
-@inject AgentJavaRuntimesManager AgentJavaRuntimesManager
-@inject InstanceManager InstanceManager
-@inject AuditLog AuditLog
 
 <h1>New Instance</h1>
-
-<Form Model="form" OnSubmit="Submit">
-  @{ var selectedAgent = form.SelectedAgent; }
-  <div class="row">
-    <div class="col-xl-7 mb-3">
-      <FormSelectInput Id="instance-agent" Label="Agent" @bind-Value="form.SelectedAgentGuid">
-        <option value="" selected>Select which agent will run the instance...</option>
-        @foreach (var agent in form.AgentsByGuid.Values.OrderBy(static agent => agent.Name)) {
-          <option value="@agent.Guid">
-            @agent.Name
-            &bullet;
-            @(agent.Stats?.RunningInstanceCount.ToString() ?? "?")/@(agent.MaxInstances) @(agent.MaxInstances == 1 ? "Instance" : "Instances")
-            &bullet;
-            @(agent.Stats?.RunningInstanceMemory.InMegabytes.ToString() ?? "?")/@(agent.MaxMemory.InMegabytes) MB RAM
-          </option>
-        }
-      </FormSelectInput>
-    </div>
-
-    <div class="col-xl-5 mb-3">
-      <FormTextInput Id="instance-name" Label="Instance Name" @bind-Value="form.InstanceName" />
-    </div>
-  </div>
-
-  <div class="row">
-    <div class="col-sm-6 col-xl-2 mb-3">
-      <FormSelectInput Id="instance-server-kind" Label="Server Software" @bind-Value="form.MinecraftServerKind">
-        @foreach (var kind in Enum.GetValues<MinecraftServerKind>()) {
-          <option value="@kind">@kind</option>
-        }
-      </FormSelectInput>
-    </div>
-
-    <div class="col-sm-6 col-xl-3 mb-3">
-      <FormSelectInput Id="instance-minecraft-version" Label="Minecraft Version" @bind-Value="form.MinecraftVersion">
-        <ChildContent>
-          @foreach (var version in availableMinecraftVersions) {
-            <option value="@version.Id">@version.Id</option>
-          }
-        </ChildContent>
-        <GroupContent>
-          <button class="btn btn-secondary dropdown-toggle" type="button" data-bs-toggle="dropdown" aria-expanded="false">@minecraftVersionType.ToNiceNamePlural()</button>
-          <ul class="dropdown-menu dropdown-menu-end">
-            @foreach (var versionType in MinecraftVersionTypes.WithServerJars) {
-              <li>
-                <button class="dropdown-item" @onclick="() => SetMinecraftVersionType(versionType)">@versionType.ToNiceNamePlural()</button>
-              </li>
-            }
-          </ul>
-        </GroupContent>
-      </FormSelectInput>
-    </div>
-
-    <div class="col-xl-3 mb-3">
-      <FormSelectInput Id="instance-java-runtime" Label="Java Runtime" @bind-Value="form.JavaRuntimeGuid" disabled="@(form.JavaRuntimesForSelectedAgent.IsEmpty)">
-        <option value="" selected>Select Java runtime...</option>
-        @foreach (var (guid, runtime) in form.JavaRuntimesForSelectedAgent) {
-          <option value="@guid">@runtime.DisplayName</option>
-        }
-      </FormSelectInput>
-    </div>
-
-    @{
-      string? allowedServerPorts = selectedAgent?.AllowedServerPorts?.ToString();
-      string? allowedRconPorts = selectedAgent?.AllowedRconPorts?.ToString();
-    }
-    <div class="col-sm-6 col-xl-2 mb-3">
-      <FormNumberInput Id="instance-server-port" @bind-Value="form.ServerPort" min="0" max="65535">
-        <LabelFragment>
-          @if (string.IsNullOrEmpty(allowedServerPorts)) {
-            <text>Server Port</text>
-          }
-          else {
-            <text>Server Port <sup title="Allowed: @allowedServerPorts">[?]</sup></text>
-          }
-        </LabelFragment>
-      </FormNumberInput>
-    </div>
-
-    <div class="col-sm-6 col-xl-2 mb-3">
-      <FormNumberInput Id="instance-rcon-port" @bind-Value="form.RconPort" min="0" max="65535">
-        <LabelFragment>
-          @if (string.IsNullOrEmpty(allowedRconPorts)) {
-            <text>Rcon Port</text>
-          }
-          else {
-            <text>Rcon Port <sup title="Allowed: @allowedRconPorts">[?]</sup></text>
-          }
-        </LabelFragment>
-      </FormNumberInput>
-    </div>
-  </div>
-
-  <div class="row">
-    <div class="col-xl-12 mb-3">
-      @{
-        const ushort MinimumMemoryUnits = 2;
-        ushort maximumMemoryUnits = form.MaximumMemoryUnits;
-        double availableMemoryRatio = maximumMemoryUnits <= MinimumMemoryUnits ? 100.0 : 100.0 * (form.AvailableMemoryUnits - MinimumMemoryUnits) / (maximumMemoryUnits - MinimumMemoryUnits);
-        // TODO not precise because the track is not centered on the track bar
-        string memoryInputSplitVar = FormattableString.Invariant($"--range-split: {Math.Round(availableMemoryRatio, 2)}%");
-      }
-      <FormNumberInput Id="instance-memory" Type="FormNumberInputType.Range" DebounceMillis="0" DisableTwoWayBinding="true" @bind-Value="form.MemoryUnits" min="@MinimumMemoryUnits" max="@maximumMemoryUnits" disabled="@(maximumMemoryUnits == 0)" class="form-range split-danger" style="@memoryInputSplitVar">
-        <LabelFragment>
-          @if (maximumMemoryUnits == 0) {
-            <text>RAM</text>
-          }
-          else {
-            <text>RAM &bullet; <code>@(form.MemoryAllocation?.InMegabytes ?? 0) / @(selectedAgent?.MaxMemory.InMegabytes) MB</code></text>
-          }
-        </LabelFragment>
-      </FormNumberInput>
-    </div>
-  </div>
-
-  <div class="row">
-    <div class="mb-3">
-      <FormTextInput Id="instance-jvm-arguments" Type="FormTextInputType.Textarea" @bind-Value="form.JvmArguments" rows="4">
-        <LabelFragment>
-          JVM Arguments <span class="text-black-50">(one per line)</span>
-        </LabelFragment>
-      </FormTextInput>
-    </div>
-  </div>
-
-  <FormButtonSubmit Label="Create Instance" class="btn btn-primary" disabled="@(!IsSubmittable)" />
-  <FormSubmitError />
-</Form>
-
-@code {
-
-  private CreateInstanceFormModel form = null!;
-
-  private MinecraftVersionType minecraftVersionType = MinecraftVersionType.Release;
-  private ImmutableArray<MinecraftVersion> availableMinecraftVersions = ImmutableArray<MinecraftVersion>.Empty;
-
-  private bool IsSubmittable => form.SelectedAgentGuid != null && !form.EditContext.GetValidationMessages(form.EditContext.Field(nameof(CreateInstanceFormModel.SelectedAgentGuid))).Any();
-
-  private readonly Guid instanceGuid = Guid.NewGuid();
-  
-  private sealed class CreateInstanceFormModel : FormModel {
-    public ImmutableDictionary<Guid, Agent> AgentsByGuid { get; }
-    private readonly ImmutableDictionary<Guid, ImmutableArray<TaggedJavaRuntime>> javaRuntimesByAgentGuid;
-
-    public CreateInstanceFormModel(AgentManager agentManager, AgentJavaRuntimesManager agentJavaRuntimesManager) {
-      AgentsByGuid = agentManager.GetAgents().Where(static agent => agent.Value.IsOnline).ToImmutableDictionary();
-      javaRuntimesByAgentGuid = agentJavaRuntimesManager.All;
-    }
-
-    private bool TryGet<TValue>(ImmutableDictionary<Guid, TValue> dictionary, Guid? agentGuid, [MaybeNullWhen(false)] out TValue value) {
-      if (agentGuid == null) {
-        value = default;
-        return false;
-      }
-      else {
-        return dictionary.TryGetValue(agentGuid.Value, out value);
-      }
-    }
-
-    private bool TryGetAgent(Guid? agentGuid, [NotNullWhen(true)] out Agent? agent) {
-      return TryGet(AgentsByGuid, agentGuid, out agent);
-    }
-
-    public Agent? SelectedAgent => TryGetAgent(SelectedAgentGuid, out var agent) ? agent : null;
-    
-    public ImmutableArray<TaggedJavaRuntime> JavaRuntimesForSelectedAgent => TryGet(javaRuntimesByAgentGuid, SelectedAgentGuid, out var javaRuntimes) ? javaRuntimes : ImmutableArray<TaggedJavaRuntime>.Empty;
-    
-    public ushort MaximumMemoryUnits => SelectedAgent?.MaxMemory.RawValue ?? 0;
-    public ushort AvailableMemoryUnits => SelectedAgent?.AvailableMemory?.RawValue ?? 0;
-    private ushort selectedMemoryUnits = 4;
-
-    [Required(ErrorMessage = "You must select an agent.")]
-    public Guid? SelectedAgentGuid { get; set; } = null;
-
-    [Required(ErrorMessage = "Instance name is required.")]
-    [StringLength(100, ErrorMessage = "Instance name must be at most 100 characters.")]
-    public string InstanceName { get; set; } = string.Empty;
-
-    [Range(minimum: 0, maximum: 65535, ErrorMessage = "Server port must be between 0 and 65535.")]
-    [ServerPortMustBeAllowed(ErrorMessage = "Server port is not allowed.")]
-    public int ServerPort { get; set; } = 25565;
-
-    [Range(minimum: 0, maximum: 65535, ErrorMessage = "Rcon port must be between 0 and 65535.")]
-    [RconPortMustBeAllowed(ErrorMessage = "Rcon port is not allowed.")]
-    [RconPortMustDifferFromServerPort(ErrorMessage = "Rcon port must not be the same as Server port.")]
-    public int RconPort { get; set; } = 25575;
-
-    public MinecraftServerKind MinecraftServerKind { get; set; } = MinecraftServerKind.Vanilla;
-
-    [Required(ErrorMessage = "You must select a Java runtime.")]
-    public Guid? JavaRuntimeGuid { get; set; }
-
-    [Required(ErrorMessage = "You must select a Minecraft version.")]
-    public string MinecraftVersion { get; set; } = string.Empty;
-
-    [Range(minimum: 0, maximum: RamAllocationUnits.MaximumUnits, ErrorMessage = "Memory is out of range.")]
-    public ushort MemoryUnits {
-      get => Math.Min(selectedMemoryUnits, MaximumMemoryUnits);
-      set => selectedMemoryUnits = value;
-    }
-
-    public RamAllocationUnits? MemoryAllocation => new RamAllocationUnits(MemoryUnits);
-
-    [JvmArgumentsMustBeValid(ErrorMessage = "JVM arguments are not valid.")]
-    public string JvmArguments { get; set; } = string.Empty;
-
-    public sealed class ServerPortMustBeAllowedAttribute : FormValidationAttribute<CreateInstanceFormModel, int> {
-      protected override string FieldName => nameof(ServerPort);
-      protected override bool IsValid(CreateInstanceFormModel model, int value) => model.SelectedAgent is not {} agent || agent.AllowedServerPorts?.Contains((ushort) value) == true;
-    }
-
-    public sealed class RconPortMustBeAllowedAttribute : FormValidationAttribute<CreateInstanceFormModel, int> {
-      protected override string FieldName => nameof(RconPort);
-      protected override bool IsValid(CreateInstanceFormModel model, int value) => model.SelectedAgent is not {} agent || agent.AllowedRconPorts?.Contains((ushort) value) == true;
-    }
-
-    public sealed class RconPortMustDifferFromServerPortAttribute : FormValidationAttribute<CreateInstanceFormModel, int?> {
-      protected override string FieldName => nameof(RconPort);
-      protected override bool IsValid(CreateInstanceFormModel model, int? value) => value != model.ServerPort;
-    }
-
-    public sealed class JvmArgumentsMustBeValidAttribute : FormCustomValidationAttribute<CreateInstanceFormModel, string> {
-      protected override string FieldName => nameof(JvmArguments);
-
-      protected override ValidationResult? Validate(CreateInstanceFormModel model, string value) {
-        var error = JvmArgumentsHelper.Validate(value);
-        return error == null ? ValidationResult.Success : new ValidationResult(error.ToSentence());
-      }
-    }
-  }
-
-  protected override void OnInitialized() {
-    form = new CreateInstanceFormModel(AgentManager, AgentJavaRuntimesManager);
-    form.EditContext.RevalidateWhenFieldChanges(tracked: nameof(CreateInstanceFormModel.SelectedAgentGuid), revalidated: nameof(CreateInstanceFormModel.MemoryUnits));
-    form.EditContext.RevalidateWhenFieldChanges(tracked: nameof(CreateInstanceFormModel.SelectedAgentGuid), revalidated: nameof(CreateInstanceFormModel.JavaRuntimeGuid));
-    form.EditContext.RevalidateWhenFieldChanges(tracked: nameof(CreateInstanceFormModel.SelectedAgentGuid), revalidated: nameof(CreateInstanceFormModel.ServerPort));
-    form.EditContext.RevalidateWhenFieldChanges(tracked: nameof(CreateInstanceFormModel.SelectedAgentGuid), revalidated: nameof(CreateInstanceFormModel.RconPort));
-    form.EditContext.RevalidateWhenFieldChanges(tracked: nameof(CreateInstanceFormModel.ServerPort), revalidated: nameof(CreateInstanceFormModel.RconPort));
-  }
-
-  protected override async Task OnInitializedAsync() {
-    await SetMinecraftVersionType(minecraftVersionType);
-  }
-
-  private async Task SetMinecraftVersionType(MinecraftVersionType type) {
-    minecraftVersionType = type;
-
-    var allMinecraftVersions = await MinecraftVersions.GetVersions(CancellationToken.None);
-    availableMinecraftVersions = allMinecraftVersions.Where(version => version.Type == type).ToImmutableArray();
-
-    if (!availableMinecraftVersions.IsEmpty) {
-      form.MinecraftVersion = availableMinecraftVersions[0].Id;
-    }
-  }
-
-  private async Task Submit(EditContext context) {
-    var selectedAgent = form.SelectedAgent;
-    if (selectedAgent == null) {
-      return;
-    }
-
-    await form.SubmitModel.StartSubmitting();
-
-    var serverPort = (ushort) form.ServerPort;
-    var rconPort = (ushort) form.RconPort;
-    var memoryAllocation = form.MemoryAllocation ?? RamAllocationUnits.Zero;
-    var javaRuntimeGuid = form.JavaRuntimeGuid.GetValueOrDefault();
-    var jvmArguments = JvmArgumentsHelper.Split(form.JvmArguments);
-
-    var instance = new InstanceConfiguration(selectedAgent.Guid, instanceGuid, form.InstanceName, serverPort, rconPort, form.MinecraftVersion, form.MinecraftServerKind, memoryAllocation, javaRuntimeGuid, jvmArguments, LaunchAutomatically: false);
-    var result = await InstanceManager.AddInstance(instance);
-    if (result.Is(AddInstanceResult.Success)) {
-      await AuditLog.AddInstanceCreatedEvent(instance.InstanceGuid);
-      Nav.NavigateTo("instances/" + instance.InstanceGuid);
-    }
-    else {
-      form.SubmitModel.StopSubmitting(result.ToSentence(AddInstanceResultExtensions.ToSentence));
-    }
-  }
-
-}
+<InstanceAddOrEditForm EditedInstanceConfiguration="null" />

Server/Phantom.Server.Web/Pages/InstanceDetail.razor

@@ -22,6 +22,9 @@ else {
       <span><!-- extra spacing --></span>
     </PermissionView>
     <InstanceStatusText Status="Instance.Status" />
+    <PermissionView Permission="Permission.CreateInstances">
+      <a href="instances/@InstanceGuid/edit" class="btn btn-warning ms-auto">Edit Configuration</a>
+    </PermissionView>
   </div>
   @if (lastError != null) {
     <p class="text-danger mt-2">@lastError</p>

Server/Phantom.Server.Web/Pages/InstanceEdit.razor

@@ -0,0 +1,28 @@
+@page "/instances/{InstanceGuid:guid}/edit"
+@attribute [Authorize(Permission.CreateInstancesPolicy)]
+@using Phantom.Server.Services.Instances
+@using Phantom.Common.Data.Instance
+@inherits PhantomComponent
+@inject InstanceManager InstanceManager
+
+@if (InstanceConfiguration == null) {
+  <h1>Instance Not Found</h1>
+  <p>Return to <a href="instances">all instances</a>.</p>
+}
+else {
+  <h1>Edit Instance: @InstanceConfiguration.InstanceName</h1>
+  <InstanceAddOrEditForm EditedInstanceConfiguration="InstanceConfiguration" />
+}
+
+@code {
+
+  [Parameter]
+  public Guid InstanceGuid { get; set; }
+
+  private InstanceConfiguration? InstanceConfiguration { get; set; }
+
+  protected override void OnInitialized() {
+    InstanceConfiguration = InstanceManager.GetInstanceConfiguration(InstanceGuid);
+  }
+
+}

Server/Phantom.Server.Web/Pages/Instances.razor

@@ -18,11 +18,11 @@
     <tr>
       <Column Width="200px; 28%">Agent</Column>
       <Column Width="200px; 28%">Name</Column>
-      <Column Width="120px; 11%">Version</Column>
+      <Column Width="130px; 11%">Version</Column>
       <Column Width="110px;  8%" Class="text-center">Server Port</Column>
       <Column Width="110px;  8%" Class="text-center">Rcon Port</Column>
-      <Column Width=" 85px;  8%" Class="text-end">Memory</Column>
-      <Column Width="315px">Identifier</Column>
+      <Column Width=" 90px;  8%" Class="text-end">Memory</Column>
+      <Column Width="320px">Identifier</Column>
       <Column Width="200px;  9%">Status</Column>
       <Column Width=" 75px">Actions</Column>
     </tr>

Server/Phantom.Server.Web/Pages/Users.razor

@@ -19,7 +19,7 @@
     <table class="table align-middle">
       <thead>
         <tr>
-          <Column Width="315px">Identifier</Column>
+          <Column Width="320px">Identifier</Column>
           <Column Width="125px; 40%">Username</Column>
           <Column Width="125px; 60%">Roles</Column>
           @if (canEdit) {

Server/Phantom.Server.Web/Shared/InstanceAddOrEditForm.razor

@@ -0,0 +1,341 @@
+@using Phantom.Common.Data.Minecraft
+@using Phantom.Common.Minecraft
+@using Phantom.Server.Services.Agents
+@using Phantom.Server.Services.Audit
+@using Phantom.Server.Services.Instances
+@using System.Collections.Immutable
+@using System.ComponentModel.DataAnnotations
+@using System.Diagnostics.CodeAnalysis
+@using Phantom.Server.Web.Components.Utils
+@using Phantom.Server.Web.Identity.Interfaces
+@using Phantom.Common.Data.Instance
+@using Phantom.Common.Data.Java
+@using Phantom.Common.Data
+@inject INavigation Nav
+@inject MinecraftVersions MinecraftVersions
+@inject AgentManager AgentManager
+@inject AgentJavaRuntimesManager AgentJavaRuntimesManager
+@inject InstanceManager InstanceManager
+@inject AuditLog AuditLog
+
+<Form Model="form" OnSubmit="AddOrEditInstance">
+  @{ var selectedAgent = form.SelectedAgent; }
+  <div class="row">
+    <div class="col-xl-7 mb-3">
+      @{
+        static RenderFragment GetAgentOption(Agent agent) {
+          return @<option value="@agent.Guid">
+                   @agent.Name
+                   &bullet;
+                   @(agent.Stats?.RunningInstanceCount.ToString() ?? "?")/@(agent.MaxInstances) @(agent.MaxInstances == 1 ? "Instance" : "Instances")
+                   &bullet;
+                   @(agent.Stats?.RunningInstanceMemory.InMegabytes.ToString() ?? "?")/@(agent.MaxMemory.InMegabytes) MB RAM
+                 </option>;
+        }
+      }
+      @if (EditedInstanceConfiguration == null) {
+        <FormSelectInput Id="instance-agent" Label="Agent" @bind-Value="form.SelectedAgentGuid">
+          <option value="" selected>Select which agent will run the instance...</option>
+          @foreach (var agent in form.AgentsByGuid.Values.Where(static agent => agent.IsOnline).OrderBy(static agent => agent.Name)) {
+            @GetAgentOption(agent)
+          }
+        </FormSelectInput>
+      }
+      else {
+        <FormSelectInput Id="instance-agent" Label="Agent" @bind-Value="form.SelectedAgentGuid" disabled="true">
+          @if (form.SelectedAgentGuid is {} guid && form.AgentsByGuid.TryGetValue(guid, out var agent)) {
+            @GetAgentOption(agent)
+          }
+        </FormSelectInput>
+      }
+    </div>
+
+    <div class="col-xl-5 mb-3">
+      <FormTextInput Id="instance-name" Label="Instance Name" @bind-Value="form.InstanceName" />
+    </div>
+  </div>
+
+  <div class="row">
+    <div class="col-sm-6 col-xl-2 mb-3">
+      <FormSelectInput Id="instance-server-kind" Label="Server Software" @bind-Value="form.MinecraftServerKind">
+        @foreach (var kind in Enum.GetValues<MinecraftServerKind>()) {
+          <option value="@kind">@kind</option>
+        }
+      </FormSelectInput>
+    </div>
+
+    <div class="col-sm-6 col-xl-3 mb-3">
+      <FormSelectInput Id="instance-minecraft-version" Label="Minecraft Version" @bind-Value="form.MinecraftVersion">
+        <ChildContent>
+          @foreach (var version in availableMinecraftVersions) {
+            <option value="@version.Id">@version.Id</option>
+          }
+        </ChildContent>
+        <GroupContent>
+          <button class="btn btn-secondary dropdown-toggle" type="button" data-bs-toggle="dropdown" aria-expanded="false">@minecraftVersionType.ToNiceNamePlural()</button>
+          <ul class="dropdown-menu dropdown-menu-end">
+            @foreach (var versionType in MinecraftVersionTypes.WithServerJars) {
+              <li>
+                <button type="button" class="dropdown-item" @onclick="() => SetMinecraftVersionType(versionType)">@versionType.ToNiceNamePlural()</button>
+              </li>
+            }
+          </ul>
+        </GroupContent>
+      </FormSelectInput>
+    </div>
+
+    <div class="col-xl-3 mb-3">
+      <FormSelectInput Id="instance-java-runtime" Label="Java Runtime" @bind-Value="form.JavaRuntimeGuid" disabled="@(form.JavaRuntimesForSelectedAgent.IsEmpty)">
+        <option value="" selected>Select Java runtime...</option>
+        @foreach (var (guid, runtime) in form.JavaRuntimesForSelectedAgent) {
+          <option value="@guid">@runtime.DisplayName</option>
+        }
+      </FormSelectInput>
+    </div>
+
+    @{
+      string? allowedServerPorts = selectedAgent?.AllowedServerPorts?.ToString();
+      string? allowedRconPorts = selectedAgent?.AllowedRconPorts?.ToString();
+    }
+    <div class="col-sm-6 col-xl-2 mb-3">
+      <FormNumberInput Id="instance-server-port" @bind-Value="form.ServerPort" min="0" max="65535">
+        <LabelFragment>
+          @if (string.IsNullOrEmpty(allowedServerPorts)) {
+            <text>Server Port</text>
+          }
+          else {
+            <text>Server Port <sup title="Allowed: @allowedServerPorts">[?]</sup></text>
+          }
+        </LabelFragment>
+      </FormNumberInput>
+    </div>
+
+    <div class="col-sm-6 col-xl-2 mb-3">
+      <FormNumberInput Id="instance-rcon-port" @bind-Value="form.RconPort" min="0" max="65535">
+        <LabelFragment>
+          @if (string.IsNullOrEmpty(allowedRconPorts)) {
+            <text>Rcon Port</text>
+          }
+          else {
+            <text>Rcon Port <sup title="Allowed: @allowedRconPorts">[?]</sup></text>
+          }
+        </LabelFragment>
+      </FormNumberInput>
+    </div>
+  </div>
+
+  <div class="row">
+    <div class="col-xl-12 mb-3">
+      @{
+        const ushort MinimumMemoryUnits = 2;
+        ushort maximumMemoryUnits = form.MaximumMemoryUnits;
+        double availableMemoryRatio = maximumMemoryUnits <= MinimumMemoryUnits ? 100.0 : 100.0 * (form.AvailableMemoryUnits - MinimumMemoryUnits) / (maximumMemoryUnits - MinimumMemoryUnits);
+        string memoryInputSplitVar = FormattableString.Invariant($"--range-split: {Math.Round(availableMemoryRatio, 2)}%");
+      }
+      <FormNumberInput Id="instance-memory" Type="FormNumberInputType.Range" DebounceMillis="0" DisableTwoWayBinding="true" @bind-Value="form.MemoryUnits" min="@MinimumMemoryUnits" max="@maximumMemoryUnits" disabled="@(maximumMemoryUnits == 0)" class="form-range split-danger" style="@memoryInputSplitVar">
+        <LabelFragment>
+          @if (maximumMemoryUnits == 0) {
+            <text>RAM</text>
+          }
+          else {
+            <text>RAM &bullet; <code>@(form.MemoryAllocation?.InMegabytes ?? 0) / @(selectedAgent?.MaxMemory.InMegabytes) MB</code></text>
+          }
+        </LabelFragment>
+      </FormNumberInput>
+    </div>
+  </div>
+
+  <div class="row">
+    <div class="mb-3">
+      <FormTextInput Id="instance-jvm-arguments" Type="FormTextInputType.Textarea" @bind-Value="form.JvmArguments" rows="4">
+        <LabelFragment>
+          JVM Arguments <span class="text-black-50">(one per line)</span>
+        </LabelFragment>
+      </FormTextInput>
+    </div>
+  </div>
+
+  <FormButtonSubmit Label="@(EditedInstanceConfiguration == null ? "Create Instance" : "Edit Instance")" class="btn btn-primary" disabled="@(!IsSubmittable)" />
+  <FormSubmitError />
+</Form>
+
+@code {
+
+  [Parameter, EditorRequired]
+  public InstanceConfiguration? EditedInstanceConfiguration { get; set; }
+
+  private ConfigureInstanceFormModel form = null!;
+
+  private MinecraftVersionType minecraftVersionType = MinecraftVersionType.Release;
+  private ImmutableArray<MinecraftVersion> availableMinecraftVersions = ImmutableArray<MinecraftVersion>.Empty;
+
+  private bool IsSubmittable => form.SelectedAgentGuid != null && !form.EditContext.GetValidationMessages(form.EditContext.Field(nameof(ConfigureInstanceFormModel.SelectedAgentGuid))).Any();
+
+  private sealed class ConfigureInstanceFormModel : FormModel {
+    public ImmutableDictionary<Guid, Agent> AgentsByGuid { get; }
+    private readonly ImmutableDictionary<Guid, ImmutableArray<TaggedJavaRuntime>> javaRuntimesByAgentGuid;
+    private readonly RamAllocationUnits? editedInstanceRamAllocation;
+
+    public ConfigureInstanceFormModel(AgentManager agentManager, AgentJavaRuntimesManager agentJavaRuntimesManager, RamAllocationUnits? editedInstanceRamAllocation) {
+      this.AgentsByGuid = agentManager.GetAgents().ToImmutableDictionary();
+      this.javaRuntimesByAgentGuid = agentJavaRuntimesManager.All;
+      this.editedInstanceRamAllocation = editedInstanceRamAllocation;
+    }
+
+    private bool TryGet<TValue>(ImmutableDictionary<Guid, TValue> dictionary, Guid? agentGuid, [MaybeNullWhen(false)] out TValue value) {
+      if (agentGuid == null) {
+        value = default;
+        return false;
+      }
+      else {
+        return dictionary.TryGetValue(agentGuid.Value, out value);
+      }
+    }
+
+    private bool TryGetAgent(Guid? agentGuid, [NotNullWhen(true)] out Agent? agent) {
+      return TryGet(AgentsByGuid, agentGuid, out agent);
+    }
+
+    public Agent? SelectedAgent => TryGetAgent(SelectedAgentGuid, out var agent) ? agent : null;
+    
+    public ImmutableArray<TaggedJavaRuntime> JavaRuntimesForSelectedAgent => TryGet(javaRuntimesByAgentGuid, SelectedAgentGuid, out var javaRuntimes) ? javaRuntimes : ImmutableArray<TaggedJavaRuntime>.Empty;
+    
+    public ushort MaximumMemoryUnits => SelectedAgent?.MaxMemory.RawValue ?? 0;
+    public ushort AvailableMemoryUnits => Math.Min((SelectedAgent?.AvailableMemory + editedInstanceRamAllocation)?.RawValue ?? MaximumMemoryUnits, MaximumMemoryUnits);
+    private ushort selectedMemoryUnits = 4;
+
+    [Required(ErrorMessage = "You must select an agent.")]
+    public Guid? SelectedAgentGuid { get; set; } = null;
+
+    [Required(ErrorMessage = "Instance name is required.")]
+    [StringLength(100, ErrorMessage = "Instance name must be at most 100 characters.")]
+    public string InstanceName { get; set; } = string.Empty;
+
+    [Range(minimum: 0, maximum: 65535, ErrorMessage = "Server port must be between 0 and 65535.")]
+    [ServerPortMustBeAllowed(ErrorMessage = "Server port is not allowed.")]
+    public int ServerPort { get; set; } = 25565;
+
+    [Range(minimum: 0, maximum: 65535, ErrorMessage = "Rcon port must be between 0 and 65535.")]
+    [RconPortMustBeAllowed(ErrorMessage = "Rcon port is not allowed.")]
+    [RconPortMustDifferFromServerPort(ErrorMessage = "Rcon port must not be the same as Server port.")]
+    public int RconPort { get; set; } = 25575;
+
+    public MinecraftServerKind MinecraftServerKind { get; set; } = MinecraftServerKind.Vanilla;
+
+    [Required(ErrorMessage = "You must select a Java runtime.")]
+    public Guid? JavaRuntimeGuid { get; set; }
+
+    [Required(ErrorMessage = "You must select a Minecraft version.")]
+    public string MinecraftVersion { get; set; } = string.Empty;
+
+    [Range(minimum: 0, maximum: RamAllocationUnits.MaximumUnits, ErrorMessage = "Memory is out of range.")]
+    public ushort MemoryUnits {
+      get => Math.Min(selectedMemoryUnits, MaximumMemoryUnits);
+      set => selectedMemoryUnits = value;
+    }
+
+    public RamAllocationUnits? MemoryAllocation => new RamAllocationUnits(MemoryUnits);
+
+    [JvmArgumentsMustBeValid(ErrorMessage = "JVM arguments are not valid.")]
+    public string JvmArguments { get; set; } = string.Empty;
+
+    public sealed class ServerPortMustBeAllowedAttribute : FormValidationAttribute<ConfigureInstanceFormModel, int> {
+      protected override string FieldName => nameof(ServerPort);
+      protected override bool IsValid(ConfigureInstanceFormModel model, int value) => model.SelectedAgent is not {} agent || agent.AllowedServerPorts?.Contains((ushort) value) == true;
+    }
+
+    public sealed class RconPortMustBeAllowedAttribute : FormValidationAttribute<ConfigureInstanceFormModel, int> {
+      protected override string FieldName => nameof(RconPort);
+      protected override bool IsValid(ConfigureInstanceFormModel model, int value) => model.SelectedAgent is not {} agent || agent.AllowedRconPorts?.Contains((ushort) value) == true;
+    }
+
+    public sealed class RconPortMustDifferFromServerPortAttribute : FormValidationAttribute<ConfigureInstanceFormModel, int?> {
+      protected override string FieldName => nameof(RconPort);
+      protected override bool IsValid(ConfigureInstanceFormModel model, int? value) => value != model.ServerPort;
+    }
+
+    public sealed class JvmArgumentsMustBeValidAttribute : FormCustomValidationAttribute<ConfigureInstanceFormModel, string> {
+      protected override string FieldName => nameof(JvmArguments);
+
+      protected override ValidationResult? Validate(ConfigureInstanceFormModel model, string value) {
+        var error = JvmArgumentsHelper.Validate(value);
+        return error == null ? ValidationResult.Success : new ValidationResult(error.ToSentence());
+      }
+    }
+  }
+
+  protected override void OnInitialized() {
+    form = new ConfigureInstanceFormModel(AgentManager, AgentJavaRuntimesManager, EditedInstanceConfiguration?.MemoryAllocation);
+    
+    if (EditedInstanceConfiguration != null) {
+      form.SelectedAgentGuid = EditedInstanceConfiguration.AgentGuid;
+      form.InstanceName = EditedInstanceConfiguration.InstanceName;
+      form.ServerPort = EditedInstanceConfiguration.ServerPort;
+      form.RconPort = EditedInstanceConfiguration.RconPort;
+      form.MinecraftVersion = EditedInstanceConfiguration.MinecraftVersion;
+      form.MinecraftServerKind = EditedInstanceConfiguration.MinecraftServerKind;
+      form.MemoryUnits = EditedInstanceConfiguration.MemoryAllocation.RawValue;
+      form.JavaRuntimeGuid = EditedInstanceConfiguration.JavaRuntimeGuid;
+      form.JvmArguments = JvmArgumentsHelper.Join(EditedInstanceConfiguration.JvmArguments);
+    }
+    
+    form.EditContext.RevalidateWhenFieldChanges(tracked: nameof(ConfigureInstanceFormModel.SelectedAgentGuid), revalidated: nameof(ConfigureInstanceFormModel.MemoryUnits));
+    form.EditContext.RevalidateWhenFieldChanges(tracked: nameof(ConfigureInstanceFormModel.SelectedAgentGuid), revalidated: nameof(ConfigureInstanceFormModel.JavaRuntimeGuid));
+    form.EditContext.RevalidateWhenFieldChanges(tracked: nameof(ConfigureInstanceFormModel.SelectedAgentGuid), revalidated: nameof(ConfigureInstanceFormModel.ServerPort));
+    form.EditContext.RevalidateWhenFieldChanges(tracked: nameof(ConfigureInstanceFormModel.SelectedAgentGuid), revalidated: nameof(ConfigureInstanceFormModel.RconPort));
+    form.EditContext.RevalidateWhenFieldChanges(tracked: nameof(ConfigureInstanceFormModel.ServerPort), revalidated: nameof(ConfigureInstanceFormModel.RconPort));
+  }
+
+  protected override async Task OnInitializedAsync() {
+    if (EditedInstanceConfiguration != null) {
+      var allMinecraftVersions = await MinecraftVersions.GetVersions(CancellationToken.None);
+      minecraftVersionType = allMinecraftVersions.FirstOrDefault(version => version.Id == EditedInstanceConfiguration.MinecraftVersion)?.Type ?? minecraftVersionType;
+    }
+
+    await SetMinecraftVersionType(minecraftVersionType);
+  }
+
+  private async Task SetMinecraftVersionType(MinecraftVersionType type) {
+    minecraftVersionType = type;
+
+    var allMinecraftVersions = await MinecraftVersions.GetVersions(CancellationToken.None);
+    availableMinecraftVersions = allMinecraftVersions.Where(version => version.Type == type).ToImmutableArray();
+
+    if (!availableMinecraftVersions.IsEmpty && !allMinecraftVersions.Any(version => version.Id == form.MinecraftVersion)) {
+      form.MinecraftVersion = availableMinecraftVersions[0].Id;
+    }
+  }
+
+  private async Task AddOrEditInstance(EditContext context) {
+    var selectedAgent = form.SelectedAgent;
+    if (selectedAgent == null) {
+      return;
+    }
+
+    await form.SubmitModel.StartSubmitting();
+
+    var instance = new InstanceConfiguration(
+      EditedInstanceConfiguration?.AgentGuid ?? selectedAgent.Guid,
+      EditedInstanceConfiguration?.InstanceGuid ?? Guid.NewGuid(),
+      form.InstanceName,
+      (ushort) form.ServerPort,
+      (ushort) form.RconPort,
+      form.MinecraftVersion,
+      form.MinecraftServerKind,
+      form.MemoryAllocation ?? RamAllocationUnits.Zero,
+      form.JavaRuntimeGuid.GetValueOrDefault(),
+      JvmArgumentsHelper.Split(form.JvmArguments),
+      EditedInstanceConfiguration?.LaunchAutomatically ?? false
+    );
+
+    var result = await InstanceManager.AddOrEditInstance(instance);
+    if (result.Is(AddOrEditInstanceResult.Success)) {
+      await (EditedInstanceConfiguration == null ? AuditLog.AddInstanceCreatedEvent(instance.InstanceGuid) : AuditLog.AddInstanceEditedEvent(instance.InstanceGuid));
+      Nav.NavigateTo("instances/" + instance.InstanceGuid);
+    }
+    else {
+      form.SubmitModel.StopSubmitting(result.ToSentence(AddOrEditInstanceResultExtensions.ToSentence));
+    }
+  }
+  
+}

Server/Phantom.Server.Web/wwwroot/css/site.css

@@ -45,6 +45,10 @@ code {
   word-break: break-word;
 }
 
+.btn {
+  text-shadow: 1px 1px 4px rgba(0, 0, 0, 0.25);
+}
+
 .table {
   margin-top: 0.5rem;
 }
@@ -61,8 +65,13 @@ code {
   height: 2.5rem;
 }
 
-.form-range.split-danger::-moz-range-track,
+.form-range.split-danger::-moz-range-track {
+  width: calc(100% - 1rem);
+  background: linear-gradient(to right, #dfd7ca 0%, #dfd7ca var(--range-split), #bf8282 var(--range-split), #bf8282 100%);
+}
+
 .form-range.split-danger::-webkit-slider-runnable-track {
+  /* centering fix does not work in Chrome */
   background: linear-gradient(to right, #dfd7ca 0%, #dfd7ca var(--range-split), #bf8282 var(--range-split), #bf8282 100%);
 }