Inno Setup IIS Installation and Configuration

we are using also IIS and thinking about to automate the IIS installation. As far as I know is it possible to do all the stuff via command line tools. So you can create your own Inno Custom Pages to retrieve the necessary data from the user. (You can use the Inno Setup Form Designer for this). Once you've collected all your stuff, you can create and then fill your prepared template batch files and in the post install the batches will be executed.

I would try it like this:

• try to do everything with a batch file concerning your IIS installation (Take a look at this archived page
• when you can do anything with batch files for the IIS Configuration, then you need to make template batch files for the Inno setup
• create custom pages for Inno to retrieve the necessary data
• in Inno, replace the template batches with the variables
• execute the batches in Inno

Hope this helps

Here is my complete code to handle IIS (Internet Information Services) with Inno Setup. It contains:

• Installation of .NET Framework 4
• Install/Uninstall of IIS+ASP.NET 4
• Registration and removal of Web-Sites/Apps
• Helper to get user-account an app pool is running on
• Helper to get physical path to a Web-Site

It has been tested with the following Windows editions: XP Pro SP3 x86, 2003 R2 x86, 2003 R2 x64, Vista Ultimate x64, 7 Home Premium x64, 2008 R2 x64, 2011 x64, 8.1 Pro x86, 10 Pro x64

Everything is done as passive as possible to not break any existing Web-Sites.

Important

This might need the Unicode-Version of Inno-Setup (I'm using 5.5.6(u)). It is also required to force 64-bit mode on x64 machines (otherwise registry and file access will redirect to 32-bit stuff):

[Setup]
ArchitecturesInstallIn64BitMode=x64

Required Helpers

• Some constants
• ExpandEnvironmentStrings => https://msdn.microsoft.com/en-us/library/windows/desktop/ms724265%28v=vs.85%29.aspx
• ExecWithResult => Reads what is written to STDOUT
• IIs7ExecAppCmd => Required for IIS installation since Vista/2008

#ifdef UNICODE
#define AW "W"
#else
#define AW "A"
#endif

const
  // See https://msdn.microsoft.com/en-us/library/windows/desktop/ms681382.aspx
  ERROR_SUCCESS = 0;
  ERROR_INVALID_FUNCTION = 1;
  ERROR_NOT_SUPPORTED = 50;
  ERROR_NOT_FOUND = 1168;
  ERROR_SUCCESS_REBOOT_REQUIRED = 3010;

function ExpandEnvironmentStrings(lpSrc: String; lpDst: String; nSize: DWORD): DWORD;
  external 'ExpandEnvironmentStrings{#AW}@kernel32.dll stdcall';
function ExpandEnvVars(const Input: String): String;
var
  Buf: String;
  BufSize: DWORD;
begin
  BufSize := ExpandEnvironmentStrings(Input, #0, 0);
  if BufSize > 0 then
  begin
    SetLength(Buf, BufSize);
    if ExpandEnvironmentStrings(Input, Buf, BufSize) = 0 then
      RaiseException(Format('Expanding env. strings failed. %s', [SysErrorMessage(DLLGetLastError)]));
#if AW == "A"
    Result := Copy(Buf, 1, BufSize - 2);
#else
    Result := Copy(Buf, 1, BufSize - 1);
#endif
  end
  else
    RaiseException(Format('Expanding env. strings failed. %s', [SysErrorMessage(DLLGetLastError)]));
end;

// Exec with output stored in result. ResultString will only be altered if True is returned.
function ExecWithResult(const Filename, Params, WorkingDir: String; const ShowCmd: Integer; const Wait: TExecWait; var ResultCode: Integer; var ResultString: String): Boolean;
var
  TempFilename: String;
  TempAnsiStr: AnsiString;
  Command: String;
begin
  TempFilename := ExpandConstant('{tmp}\~execwithresult.txt');
  // Exec via cmd and redirect output to file. Must use special string-behavior to work.
  Command := Format('"%s" /S /C ""%s" %s > "%s""', [ExpandConstant('{cmd}'), Filename, Params, TempFilename]);
  Result := Exec(ExpandConstant('{cmd}'), Command, WorkingDir, ShowCmd, Wait, ResultCode);
  if not Result then
    Exit;
  LoadStringFromFile(TempFilename, TempAnsiStr);  // Cannot fail
  ResultString := String(TempAnsiStr);
  DeleteFile(TempFilename);
  // Remove new-line at the end
  if (Length(ResultString) >= 2) and (ResultString[Length(ResultString) - 1] = #13) and (ResultString[Length(ResultString)] = #10) then
    Delete(ResultString, Length(ResultString) - 1, 2);
end;

function IIs7ExecAppCmd(Params: String; var ResultString: String; var ResultCode: Integer): Boolean;
var
  AppCmdFilePath: String;
  Command: String;
begin
  AppCmdFilePath := ExpandConstant('{sys}\inetsrv\appcmd.exe');
  Result := ExecWithResult(AppCmdFilePath, Params, '', SW_HIDE, ewWaitUntilTerminated, ResultCode, ResultString);
end;

.NET 4 Installation

Will install .NET 4.0 for Win XP/2003. .NET 4.6 for Vista/2008 and later. Will do nothing if .NET 4 is already included with the system (Win 8/2012/10). The following files are required and must be included in the setup:

• .NET 4.0 Web-Installer "dotNetFx40_Full_setup.exe" => https://www.microsoft.com/en-US/download/details.aspx?id=17851
• .NET 4.6 Web-Installer "NDP46-KB3045560-Web.exe" => https://www.microsoft.com/de-de/download/details.aspx?id=48130
• WIC x64 "wic_x64_enu.exe" => https://www.microsoft.com/de-de/download/details.aspx?id=1385
• WIC x86 "wic_x86_enu.exe" => https://www.microsoft.com/de-de/download/details.aspx?id=32

-

[Files]
Source: "dotNetFx40_Full_setup.exe"; DestDir: "{tmp}"; Flags: ignoreversion dontcopy
Source: "NDP46-KB3045560-Web.exe"; DestDir: "{tmp}"; Flags: ignoreversion dontcopy
Source: "wic_x64_enu.exe"; DestDir: "{tmp}"; Flags: ignoreversion dontcopy
Source: "wic_x86_enu.exe"; DestDir: "{tmp}"; Flags: ignoreversion dontcopy

Since I'm using the Web-Installers, an internet connection might be required during installation.

// Checks if .NET 4 "Full" is installed
function IsDotNet4FullInstalled(): Boolean;
var
  Success: Boolean;
  Install: Cardinal;
begin
  try
    ExpandConstant('{dotnet40}');  // This will throw an exception if .NET 4 is not installed at all
    Success := RegQueryDWordValue(HKLM, 'SOFTWARE\Microsoft\NET Framework Setup\NDP\v4\Full', 'Install', Install);  // Check for "Full" version
    Result := Success and (Install = 1);
  except
    Result := False;
  end;
end;

// Returns True if a restart is required.
function InstallDotNet4(): Boolean;
var
  Version: TWindowsVersion;
  ResultCode: Integer;
  Success: Boolean;
begin
  GetWindowsVersionEx(Version);
  if (Version.Major <= 5) then  // 4.0 for XP, 2003
    ExtractTemporaryFile('dotNetFx40_Full_setup.exe')
  else  // 4.6
    ExtractTemporaryFile('NDP46-KB3045560-Web.exe');
  if (Version.Major <= 5) then  // XP, 2003: Install .NET 4.0
  begin
    Success := Exec(ExpandConstant('{tmp}\dotNetFx40_Full_setup.exe'), '/passive', '', SW_HIDE, ewWaitUntilTerminated, ResultCode);
    if Success and (ResultCode = 5100) then  // Indicates that "Windows Imaging Component" is missing (probably 2003)
    begin
      if IsWin64 then
      begin
        ExtractTemporaryFile('wic_x64_enu.exe');
        if not Exec(ExpandConstant('{tmp}\wic_x64_enu.exe'), '/passive', '', SW_HIDE, ewWaitUntilTerminated, ResultCode) or (ResultCode <> ERROR_SUCCESS) then
          RaiseException('Failed to install "Windows Imaging Component": ' + SysErrorMessage(ResultCode) + ' (' + IntToStr(ResultCode) + ')');
        // Retry .NET
        Success := Exec(ExpandConstant('{tmp}\dotNetFx40_Full_setup.exe'), '/passive', '', SW_HIDE, ewWaitUntilTerminated, ResultCode);
      end
      else
      begin
        ExtractTemporaryFile('wic_x86_enu.exe');
        if not Exec(ExpandConstant('{tmp}\wic_x86_enu.exe'), '/passive', '', SW_HIDE, ewWaitUntilTerminated, ResultCode) or (ResultCode <> ERROR_SUCCESS) then
          RaiseException('Failed to install "Windows Imaging Component": ' + SysErrorMessage(ResultCode) + ' (' + IntToStr(ResultCode) + ')');
        // Retry .NET
        Success := Exec(ExpandConstant('{tmp}\dotNetFx40_Full_setup.exe'), '/passive', '', SW_HIDE, ewWaitUntilTerminated, ResultCode);
      end;
    end
  end
  else  // Vista / 2008 or later: Install .NET 4.6
    Success := Exec(ExpandConstant('{tmp}\NDP46-KB3045560-Web.exe'), '/passive', '', SW_HIDE, ewWaitUntilTerminated, ResultCode);
  // Check for errors
  if not Success or ((ResultCode <> ERROR_SUCCESS) and (ResultCode <> ERROR_SUCCESS_REBOOT_REQUIRED)) then
    RaiseException('Failed to install .NET: ' + SysErrorMessage(ResultCode) + ' (' + IntToStr(ResultCode) + ')');
  Result := ResultCode = ERROR_SUCCESS_REBOOT_REQUIRED;
end;

IIS Installation / Uninstall

Installs IIS with ASP.NET 4. Will activate the same (default-)features as if it was activated via GUI. After installation is completed, ASP.NET is (re-)registered with IIS.

Note: For Win XP/2003, the "Windows Installation CD" is required.

// Returns True if a restart is required. Throws exceptions.
function InstallIIs(): Boolean;
var
  Version: TWindowsVersion;
  Success: Boolean;
  ResultCode: Integer;
  IIS56IniFile: String;
begin
  GetWindowsVersionEx(Version);
  if (Version.Major <= 5) then  // XP / 2003: Use "sysocmgr"
  begin
    IIS56IniFile := ExpandConstant('{tmp}\~iis56.ini');
    SaveStringToFile(IIS56IniFile, '[Components]' + #13#10 + 'iis_common = ON' + #13#10 + 'iis_www = ON' + #13#10 + 'iis_inetmgr = ON', False);
    Success := Exec('sysocmgr', ExpandConstant('/i:"{win}\inf\sysoc.inf" /u:"' + IIS56IniFile + '"'), '', SW_SHOW, ewWaitUntilTerminated, ResultCode);
    DeleteFile(IIS56IniFile);
  end
  else if (Version.Major = 6) and (Version.Minor = 0) then  // Vista / 2008: Use "pkgmgr"
  begin
    Success := Exec('pkgmgr', '/iu:' +
      // Enables everything a fresh install would also (implicitly) enable.
      // This is important in case IIS was already installed and some features manually disabled.
      'WAS-WindowsActivationService;WAS-ProcessModel;WAS-NetFxEnvironment;WAS-ConfigurationAPI' +
      ';IIS-WebServerRole' +
      ';IIS-WebServerManagementTools;IIS-ManagementConsole' +
      ';IIS-WebServer' +
      ';IIS-ApplicationDevelopment;IIS-NetFxExtensibility;IIS-ASPNET;IIS-ISAPIExtensions;IIS-ISAPIFilter' +
      ';IIS-CommonHttpFeatures;IIS-HttpErrors;IIS-DefaultDocument;IIS-StaticContent;IIS-DirectoryBrowsing' +
      ';IIS-Performance;IIS-HttpCompressionStatic' +
      ';IIS-Security;IIS-RequestFiltering' +
      ';IIS-HealthAndDiagnostics;IIS-RequestMonitor;IIS-HttpLogging',
      '', SW_HIDE, ewWaitUntilTerminated, ResultCode);
  end
  else if (Version.Major = 6) and (Version.Minor = 1) then  // 7 / 2008 R2 / 2011: Use "Dism"
  begin
    Success := Exec('Dism', '/Online /Enable-Feature' +
      // Enables everything a fresh install would also (implicitly) enable.
      // This is important in case IIS was already installed and some features manually disabled.
      // "Parent fetaures" are NOT automatically enabled by "Dism".
      ' /FeatureName:WAS-WindowsActivationService /FeatureName:WAS-ProcessModel /FeatureName:WAS-NetFxEnvironment /FeatureName:WAS-ConfigurationAPI' +
      ' /FeatureName:IIS-WebServerRole' +
      ' /FeatureName:IIS-WebServerManagementTools /FeatureName:IIS-ManagementConsole' +
      ' /FeatureName:IIS-WebServer' +
      ' /FeatureName:IIS-ApplicationDevelopment /FeatureName:IIS-NetFxExtensibility /FeatureName:IIS-ASPNET /FeatureName:IIS-ISAPIExtensions /FeatureName:IIS-ISAPIFilter' +
      ' /FeatureName:IIS-CommonHttpFeatures /FeatureName:IIS-HttpErrors /FeatureName:IIS-DefaultDocument /FeatureName:IIS-StaticContent /FeatureName:IIS-DirectoryBrowsing' +
      ' /FeatureName:IIS-Performance /FeatureName:IIS-HttpCompressionStatic' +
      ' /FeatureName:IIS-Security /FeatureName:IIS-RequestFiltering' +
      ' /FeatureName:IIS-HealthAndDiagnostics /FeatureName:IIS-RequestMonitor /FeatureName:IIS-HttpLogging',
      '', SW_HIDE, ewWaitUntilTerminated, ResultCode);
  end
  else  // 8 / 2012 and later: Use "Dism"
  begin
    Success := Exec('Dism', '/Online /Enable-Feature' +
      // Enables everything a fresh install would also (implicitly) enable.
      // This is important in case IIS was already installed and some features manually disabled.
      ' /FeatureName:WAS-WindowsActivationService /FeatureName:WAS-ProcessModel /FeatureName:WAS-NetFxEnvironment /FeatureName:WAS-ConfigurationAPI' +
      ' /FeatureName:IIS-ManagementConsole' +
      ' /FeatureName:IIS-HttpErrors /FeatureName:IIS-DefaultDocument /FeatureName:IIS-StaticContent /FeatureName:IIS-DirectoryBrowsing' +
      ' /FeatureName:IIS-ASPNET45' +
      ' /FeatureName:IIS-HttpCompressionStatic' +
      ' /FeatureName:IIS-RequestFiltering' +
      ' /FeatureName:IIS-HttpLogging' +
      ' /All',  // Implicitly enables dependent features
      '', SW_HIDE, ewWaitUntilTerminated, ResultCode);
  end;
  if not Success or ((ResultCode <> ERROR_SUCCESS) and (ResultCode <> ERROR_SUCCESS_REBOOT_REQUIRED)) then
    RaiseException('Cannot install IIS: ' + SysErrorMessage(ResultCode) + ' (' + IntToStr(ResultCode) + ')');
  Result := ResultCode = ERROR_SUCCESS_REBOOT_REQUIRED;
  // Register ASP.NET 4 with IIS. This is required since .NET 4 was probably installed before IIS.
  // This will NOT change existing web-sites (which might be using other ASP.NET versions already)
  if not Exec(ExpandConstant('{dotnet40}') + '\aspnet_regiis.exe', '-iru -enable', '', SW_HIDE, ewWaitUntilTerminated, ResultCode) or
    (ResultCode <> ERROR_SUCCESS) then
    RaiseException('Cannot register ASP.NET: ' + SysErrorMessage(ResultCode) + ' (' + IntToStr(ResultCode) + ')');
end;

// Returns True if a restart is required. Throws exceptions.
function UninstallIIs(): Boolean;
var
  Version: TWindowsVersion;
  Success: Boolean;
  ResultCode: Integer;
  IIS56IniFile: String;
begin
  GetWindowsVersionEx(Version);
  if (Version.Major <= 5) then  // XP / 2003: Use "sysocmgr"
  begin
    IIS56IniFile := ExpandConstant('{tmp}\~iis56.ini');
    SaveStringToFile(IIS56IniFile, '[Components]' + #13#10 + 'iis_common = OFF' + #13#10 + 'iis_www = OFF' + #13#10 + 'iis_inetmgr = OFF', False);
    Success := Exec('sysocmgr', ExpandConstant('/i:"{win}\inf\sysoc.inf" /u:"' + IIS56IniFile + '"'), '', SW_SHOW, ewWaitUntilTerminated, ResultCode);
    DeleteFile(IIS56IniFile);
  end
  else if (Version.Major = 6) and (Version.Minor = 0) then  // Vista / 2008: Use "pkgmgr"
    Success := Exec('pkgmgr', '/norestart /uu:IIS-WebServerRole', '', SW_HIDE, ewWaitUntilTerminated, ResultCode)
  else  // 7 / 2008 R2 and later: Use "Dism"
    Success := Exec('Dism', '/NoRestart /Online /Disable-Feature /FeatureName:IIS-WebServerRole', '', SW_HIDE, ewWaitUntilTerminated, ResultCode);
  if not Success or ((ResultCode <> ERROR_SUCCESS) and (ResultCode <> ERROR_SUCCESS_REBOOT_REQUIRED)) then
    RaiseException('Cannot uninstall IIS: ' + SysErrorMessage(ResultCode) + ' (' + IntToStr(ResultCode) + ')');
  Result := ResultCode = ERROR_SUCCESS_REBOOT_REQUIRED;
end;

Web-Site/App Registration and Removal

Creates a virtual directory and an ASP.NET 4 Application Pool.

Note: IIsServerNumber is the actual Web-Site which usually defaults to 1 (=> "Default Web Site").

Usage:

RegisterAppAtIIs('MyAppName', 1, 'MyAppAppPoolName');
DeleteAppFromIIs('MyAppName', 1, 'MyAppAppPoolName');

// Throws exceptions.
procedure RegisterAppAtIIs(const IIsAppName: String; const IIsServerNumber: Integer; const IIsApplicationPoolName: String);
var
  Version: TWindowsVersion;
  // IIS 5.1 - 6.0
  IIS, WebService, WebSite, WebRoot, vDir, AppPools, AppPool: Variant;
  // IIS 7 and later
  ResultCode: Integer;
  ExecResult: String;
  WebSiteName: String;
begin
  GetWindowsVersionEx(Version);
  if (Version.Major = 5) and (Version.Minor <= 2) then  // XP, 2003: IIS 5.1 - 6.0
  begin
    try
      // Create the main IIS COM Automation object
      IIS := CreateOleObject('IISNamespace');
      WebService := IIS.GetObject('IIsWebService', 'localhost/W3SVC');
      // Get web site
      WebSite := WebService.GetObject('IIsWebServer', IntToStr(IIsServerNumber));
      WebRoot := WebSite.GetObject('IIsWebVirtualDir', 'Root');
    except
      RaiseException(Format('Web-site #%d not found: ', [IIsServerNumber]) + GetExceptionMessage());
    end;
    // Delete the virtual dir if it already exists
    try
      WebRoot.Delete('IIsWebVirtualDir', IIsAppName);
      WebRoot.SetInfo();
    except
    end;
    if (Version.Minor = 1) then  // XP: IIS 5.1
    begin
      // Create the virtual directory
      try
        vDir := WebRoot.Create('IIsWebVirtualDir', IIsAppName);
        vDir.AccessRead := True;
        vDir.AccessScript := True;
        vDir.AppFriendlyName := IIsAppName;
        vDir.Path := ExpandConstant('{app}');
        vDir.AppCreate(True);  // Create in "InProc" mode (don't really know why though)
        vDir.SetInfo();
      except
        RaiseException('Cannot create virtual directory: ' + GetExceptionMessage());
      end;
    end
    else if (Version.Minor = 2) then  // 2003: IIS 6.0
    begin
      // Application pool stuff
      AppPools := WebService.GetObject('IIsApplicationPools', 'AppPools');
      try
        // Check if the application pool already exists
        AppPool := AppPools.GetObject('IIsApplicationPool', IIsApplicationPoolName);
      except
        AppPool := Null;
      end;
      if VarIsNull(AppPool) then
      begin
        // Create the application pool
        try
          AppPool := AppPools.Create('IIsApplicationPool', IIsApplicationPoolName);
          AppPool.SetInfo();
        except
          RaiseException('Cannot add application pool: ' + GetExceptionMessage());
        end;
      end;
      // Create the virtual directory
      try
        vDir := WebRoot.Create('IIsWebVirtualDir', IIsAppName);
        vDir.AccessRead := True;
        vDir.AccessScript := True;
        vDir.AppFriendlyName := IIsAppName;
        vDir.Path := ExpandConstant('{app}');
        vDir.AppCreate(True);  // Create in "InProc" mode
        vDir.AppPoolId := IIsApplicationPoolName;
        vDir.SetInfo();
      except
        RaiseException('Cannot create virtual directory: ' + GetExceptionMessage());
      end;
    end;
    // Register handlers for ASP.NET 4 (important if other ASP.NET versions are present)
    if not ExecWithResult(ExpandConstant('{dotnet40}') + '\aspnet_regiis.exe',Format('-s "W3SVC/%d/ROOT/%s"', [IIsServerNumber, IIsAppName]),'',SW_HIDE,ewWaitUntilTerminated, ResultCode, ExecResult) or (ResultCode <> ERROR_SUCCESS) then
      RaiseException('Cannot set ASP.NET version: ' + SysErrorMessage(ResultCode) + ' (' + IntToStr(ResultCode) + ')');
  end
  else if (Version.Major >= 6) then  // Vista / 2008 or later : IIS 7 or later
  begin
    // Get name of web-site
    if not IIs7ExecAppCmd(Format('list site /id:%d /text:name', [IIsServerNumber]), ExecResult, ResultCode) then
      RaiseException(Format('Cannot get name of web-site #%d: ', [IIsServerNumber]) + SysErrorMessage(ResultCode) + ' (' + IntToStr(ResultCode) + ')');
    if (Length(Trim(ExecResult)) = 0) then
      RaiseException(Format('Web-site #%d not found.', [IIsServerNumber]));
    WebSiteName := ExecResult;
    // Delete the application if it already exists
    if not IIs7ExecAppCmd(Format('delete app "%s/%s"', [WebSiteName, IIsAppName]), ExecResult, ResultCode) or
      ((ResultCode <> ERROR_SUCCESS) and (ResultCode <> ERROR_NOT_FOUND) and (ResultCode <> ERROR_NOT_SUPPORTED)) then
      RaiseException('Cannot delete application: ' + SysErrorMessage(ResultCode) + ' (' + IntToStr(ResultCode) + ')');
    // Check if the application pool already exists (we don't delete it, since another GVS instance might be using it too)
    if not IIs7ExecAppCmd(Format('list apppool "%s" /text:name', [IIsApplicationPoolName]), ExecResult, ResultCode) or
      ((ResultCode <> ERROR_SUCCESS) and (ResultCode <> ERROR_INVALID_FUNCTION)) then
      RaiseException('Cannot list application pools: ' + SysErrorMessage(ResultCode) + ' (' + IntToStr(ResultCode) + ')');
    // Create the application pool
    if (ExecResult <> IIsApplicationPoolName) then
    begin
      if not IIs7ExecAppCmd(Format('add apppool /name:"%s" /managedRuntimeVersion:v4.0', [IIsApplicationPoolName]), ExecResult, ResultCode) or (ResultCode <> ERROR_SUCCESS) then
        RaiseException('Cannot add application pool: ' + SysErrorMessage(ResultCode) + ' (' + IntToStr(ResultCode) + ')');
    end;
    // Create the application
    if not IIs7ExecAppCmd(Format('add app /site.name:"%s" /path:"/%s" /physicalPath:"%s" /applicationPool:"%s"', [WebSiteName, IIsAppName, ExpandConstant('{app}'), IIsApplicationPoolName]), ExecResult, ResultCode) or
      (ResultCode <> ERROR_SUCCESS) then
      RaiseException('Cannot add application: ' + SysErrorMessage(ResultCode) + ' (' + IntToStr(ResultCode) + ')');
  end
  else
    RaiseException('Cannot register web-site: Unknown OS version.');
end;

// Throws exceptions.
procedure DeleteAppFromIIs(const IIsAppName: String; const IIsServerNumber: Integer; const IIsApplicationPoolName: String);
var
  Version: TWindowsVersion;
  // IIS 5.1 - 6.0
  IIS, WebService, WebSite, WebRoot, AppPools: Variant;
  // IIS 7 and later
  ResultCode: Integer;
  ExecResult: String;
  WebSiteName: String;
begin
  GetWindowsVersionEx(Version);
  if (Version.Major = 5) and (Version.Minor <= 2) then  // XP, 2003: IIS 5.1 - 6.0
  begin
    try
      // Create the main IIS COM Automation object
      IIS := CreateOleObject('IISNamespace');
      WebService := IIS.GetObject('IIsWebService', 'localhost/W3SVC');
      // Get web site
      WebSite := WebService.GetObject('IIsWebServer', IntToStr(IIsServerNumber));
      WebRoot := WebSite.GetObject('IIsWebVirtualDir', 'Root');
    except
      RaiseException(Format('Web-site #%d not found: ', [IIsServerNumber]) + GetExceptionMessage());
    end;
    // Delete the virtual dir
    try
      WebRoot.Delete('IIsWebVirtualDir', IIsAppName);
      WebRoot.SetInfo();
    except
    end;
    if (Version.Minor = 2) then  // 2003: IIS 6.0
    begin
      // Application pool stuff
      AppPools := WebService.GetObject('IIsApplicationPools', 'AppPools');
      try
        // Delete the application pool
        AppPools.Delete('IIsApplicationPool', IIsApplicationPoolName);
      except
      end;
    end;
  end
  else if (Version.Major >= 6) then  // Vista / 2008 or later : IIS 7 or later
  begin
    // Get name of web-site
    if not IIs7ExecAppCmd(Format('list site /id:%d /text:name', [IIsServerNumber]), ExecResult, ResultCode) then
      RaiseException(Format('Cannot get name of web-site #%d: ', [IIsServerNumber]) + SysErrorMessage(ResultCode) + ' (' + IntToStr(ResultCode) + ')');
    if (Length(Trim(ExecResult)) = 0) then
      RaiseException(Format('Web-site #%d not found.', [IIsServerNumber]));
    WebSiteName := ExecResult;
    // Delete the application
    if not IIs7ExecAppCmd(Format('delete app "%s/%s"', [WebSiteName, IIsAppName]), ExecResult, ResultCode) or
      ((ResultCode <> ERROR_SUCCESS) and (ResultCode <> ERROR_NOT_FOUND) and (ResultCode <> ERROR_NOT_SUPPORTED)) then
      RaiseException('Cannot delete application: ' + SysErrorMessage(ResultCode) + ' (' + IntToStr(ResultCode) + ')');
    // Delete the application pool
    if not IIs7ExecAppCmd(Format('delete apppool "%s"', [IIsApplicationPoolName]), ExecResult, ResultCode) or
      ((ResultCode <> ERROR_SUCCESS) and (ResultCode <> ERROR_NOT_FOUND)) then
      RaiseException('Cannot delete application pool: ' + SysErrorMessage(ResultCode) + ' (' + IntToStr(ResultCode) + ')');
  end
  else
    RaiseException('Cannot delete web-site: Unknown OS version.');
end;

Useful Helpers

Finds the Windows user-account used by ASP.NET to read/write files in the virtual directory. Useful to set permissions for "App_Data".

// Throws exceptions.
function GetIIsAppPoolIdentity(const IIsApplicationPoolName: String): String;
var
  Version: TWindowsVersion;
  ResultCode: Integer;
  ExecResult: String;
  IIS, AppPool: Variant;
begin
  GetWindowsVersionEx(Version);
  if (Version.Major = 5) and (Version.Minor = 1) then  // XP: IIS 5.1
  begin
    // TODO: Should be read from "[.NET 4]\Config\machine.config" -> system.web.processModel.userName
    // - "System"
    // - "Machine" -> "ASPNET" (default)
    // - A custom user account
    // See https://msdn.microsoft.com/en-us/library/dwc1xthy.aspx
    Result := 'ASPNET';
  end
  else if (Version.Major = 5) and (Version.Minor = 2) then  // 2003: IIS 6.0
  begin
    try
      IIS := CreateOleObject('IISNamespace');
      AppPool := IIS.GetObject('IIsApplicationPool', 'localhost/W3SVC/AppPools/' + IIsApplicationPoolName);
      if (AppPool.AppPoolIdentityType = 0) then
        Result := 'NT AUTHORITY\SYSTEM'
      else if (AppPool.AppPoolIdentityType = 1) then
        Result := 'NT AUTHORITY\LOCAL SERVICE'
      else if (AppPool.AppPoolIdentityType = 2) then
        Result := 'NT AUTHORITY\NETWORKSERVICE'
      else if (AppPool.AppPoolIdentityType = 3) then
        Result := AppPool.WAMUserName
      else
        RaiseException('Cannot get application pool identity: Unknown identity type (' + IntToStr(AppPool.AppPoolIdentityType) + ')');
    except
      RaiseException('Cannot get application pool identity: Unable to get object');
    end;
  end
  else if (Version.Major >= 6) then  // Vista / 2008 or later
  begin
    if not IIs7ExecAppCmd(Format('list apppool "%s" /text:processModel.identityType', [IIsApplicationPoolName]), ExecResult, ResultCode) or
      (ResultCode <> ERROR_SUCCESS) then
      RaiseException('Cannot get application pool identity.');
    if (ExecResult = 'LocalSystem') then
      Result := 'NT AUTHORITY\SYSTEM'
    else if (ExecResult = 'LocalService') then
      Result := 'NT AUTHORITY\LOCAL SERVICE'
    else if (ExecResult = 'NetworkService') then
      Result := 'NT AUTHORITY\NETWORKSERVICE'
    else if (ExecResult = 'ApplicationPoolIdentity') then
      Result := 'IIS AppPool\' + IIsApplicationPoolName
    else
      RaiseException('Cannot get application pool identity: Unknown identity type "' + ExecResult + '"');
  end
  else
    RaiseException('Cannot get application pool identity: Unknown OS version: ' + IntToStr(Version.Major) + '.' + IntToStr(Version.Minor));
end;

Returns the physical path to a Web-Site. Useful to find the correct place to install files to.

// Throws exceptions.
function IIsGetPhysicalPath(const IIsServerNumber: Integer): String;
var
  Version: TWindowsVersion;
  IIS, WebService, WebSite, WebRoot: Variant;
  ResultCode: Integer;
  ExecResult: String;
  WebSiteName: String;
  PhysPath: String;
begin
  GetWindowsVersionEx(Version);
  if (Version.Major = 5) then
  begin
    try
      // Create the main IIS COM Automation object
      IIS := CreateOleObject('IISNamespace');
      WebService := IIS.GetObject('IIsWebService', 'localhost/W3SVC');
      // Get web site
      WebSite := WebService.GetObject('IIsWebServer', IntToStr(IIsServerNumber));
      WebRoot := WebSite.GetObject('IIsWebVirtualDir', 'Root');
    except
      RaiseException(Format('Web-site #%d not found: ', [IIsServerNumber]) + GetExceptionMessage());
    end;
    PhysPath := WebRoot.Path;
  end
  else if (Version.Major >= 6) then  // Vista / 2008 or later
  begin
    // Get name of web-site
    if not IIs7ExecAppCmd(Format('list site /id:%d /text:name', [IIsServerNumber]), ExecResult, ResultCode) then
      RaiseException(Format('Cannot get name of web-site #%d: ', [IIsServerNumber]) + SysErrorMessage(ResultCode) + ' (' + IntToStr(ResultCode) + ')');
    if (Length(Trim(ExecResult)) = 0) then
      RaiseException(Format('Web-site #%d not found.', [IIsServerNumber]));
    WebSiteName := ExecResult;
    // Get physical path
    if not IIs7ExecAppCmd(Format('list vdir /app.name:"%s"/ /text:physicalPath', [WebSiteName]), ExecResult, ResultCode) or
      (ResultCode <> ERROR_SUCCESS) then
      RaiseException(Format('Cannot get physical path to web-site "%s": ', [WebSiteName]) + SysErrorMessage(ResultCode) + ' (' + IntToStr(ResultCode) + ')');
    PhysPath := ExecResult;
  end
  else
    RaiseException('Cannot get physical path to web-site root: Unknown OS version: ' + IntToStr(Version.Major) + '.' + IntToStr(Version.Minor));
  // Expand environment variables in path (e.g. "%SystemDrive%")
  Result := ExpandEnvVars(PhysPath);
end;

So, in the end what I did was create a separate executable coded in C# which will install IIS through the command line before installation and will then register IIS with the appropriate application pool etc after installation. I then proceeded to call the executable through Inno Setup in PrepareToInstall to install IIS, and in CurStepChanged to register IIS.