Common Cloud Service (classic) startup tasks

Article
07/23/2024

Important

Cloud Services (classic) is now deprecated for all customers as of September 1st, 2024. Any existing running deployments will be stopped and shut down by Microsoft and the data will be permanantly lost starting October 2024. New deployments should use the new Azure Resource Manager based deployment model Azure Cloud Services (extended support).

This article provides some examples of common startup tasks you may want to perform in your cloud service. You can use startup tasks to perform operations before a role starts. Operations that you might want to perform include installing a component, registering Component Object Model (COM) components, setting registry keys, or starting a long running process.

See this article to understand how startup tasks work, and specifically how to create the entries that define a startup task.

Note

Startup tasks are not applicable to Virtual Machines, only to Cloud Service Web and Worker roles.

Define environment variables before a role starts

If you need environment variables defined for a specific task, use the Environment element inside the Task element.

<ServiceDefinition name="MyService" xmlns="http://schemas.microsoft.com/ServiceHosting/2008/10/ServiceDefinition">
    <WorkerRole name="WorkerRole1">
        ...
        <Startup>
            <Task commandLine="Startup.cmd" executionContext="limited" taskType="simple">
                <Environment>
                    <Variable name="MyEnvironmentVariable" value="MyVariableValue" />
                </Environment>
            </Task>
        </Startup>
    </WorkerRole>
</ServiceDefinition>

Variables can also use a valid Azure XPath value to reference something about the deployment. Instead of using the value attribute, define a RoleInstanceValue child element.

<Variable name="PathToStartupStorage">
    <RoleInstanceValue xpath="/RoleEnvironment/CurrentInstance/LocalResources/LocalResource[@name='StartupLocalStorage']/@path" />
</Variable>

Configure IIS startup with AppCmd.exe

The AppCmd.exe command-line tool can be used to manage Internet Information Service (IIS) settings at startup on Azure. AppCmd.exe provides convenient, command-line access to configuration settings for use in startup tasks on Azure. When you use AppCmd.exe, Website settings can be added, modified, or removed for applications and sites.

However, there are a few things to watch out for in the use of AppCmd.exe as a startup task:

Startup tasks can be run more than once between reboots. For instance, when a role recycles.
If a AppCmd.exe action is performed more than once, it may generate an error. For example, attempting to add a section to Web.config twice could generate an error.
Startup tasks fail if they return a nonzero exit code or errorlevel. For example, when AppCmd.exe generates an error.

It's a good practice to check the errorlevel after calling AppCmd.exe, which is easy to do if you wrap the call to AppCmd.exe with a .cmd file. If you detect a known errorlevel response, you can ignore it, or pass it back.

The errorlevel values returned by AppCmd.exe are listed in the winerror.h file and can also be seen on the Microsoft Developer Network (MSDN).

Example of managing the error level

This example adds a compression section and a compression entry for JSON to the Web.config file, with error handling and logging.

The relevant sections of the ServiceDefinition.csdef file are shown here, which include setting the executionContext attribute to elevated to give AppCmd.exe sufficient permissions to change the settings in the Web.config file:

<ServiceDefinition name="MyService" xmlns="http://schemas.microsoft.com/ServiceHosting/2008/10/ServiceDefinition">
    <WorkerRole name="WorkerRole1">
        ...
        <Startup>
            <Task commandLine="Startup.cmd" executionContext="elevated" taskType="simple" />
        </Startup>
    </WorkerRole>
</ServiceDefinition>

The Startup.cmd batch file uses AppCmd.exe to add a compression section and a compression entry for JSON to the Web.config file. The expected errorlevel of 183 is set to zero using the VERIFY.EXE command-line program. Unexpected errorlevels are logged to StartupErrorLog.txt.

REM   *** Add a compression section to the Web.config file. ***
%windir%\system32\inetsrv\appcmd set config /section:urlCompression /doDynamicCompression:True /commit:apphost >> "%TEMP%\StartupLog.txt" 2>&1

REM   ERRORLEVEL 183 occurs when trying to add a section that already exists. This error is expected if this
REM   batch file were executed twice. This can occur and must be accounted for in an Azure startup
REM   task. To handle this situation, set the ERRORLEVEL to zero by using the Verify command. The Verify
REM   command will safely set the ERRORLEVEL to zero.
IF %ERRORLEVEL% EQU 183 VERIFY > NUL

REM   If the ERRORLEVEL is not zero at this point, some other error occurred.
IF %ERRORLEVEL% NEQ 0 (
    ECHO Error adding a compression section to the Web.config file. >> "%TEMP%\StartupLog.txt" 2>&1
    GOTO ErrorExit
)

REM   *** Add compression for json. ***
%windir%\system32\inetsrv\appcmd set config  -section:system.webServer/httpCompression /+"dynamicTypes.[mimeType='application/json; charset=utf-8',enabled='True']" /commit:apphost >> "%TEMP%\StartupLog.txt" 2>&1
IF %ERRORLEVEL% EQU 183 VERIFY > NUL
IF %ERRORLEVEL% NEQ 0 (
    ECHO Error adding the JSON compression type to the Web.config file. >> "%TEMP%\StartupLog.txt" 2>&1
    GOTO ErrorExit
)

REM   *** Exit batch file. ***
EXIT /b 0

REM   *** Log error and exit ***
:ErrorExit
REM   Report the date, time, and ERRORLEVEL of the error.
DATE /T >> "%TEMP%\StartupLog.txt" 2>&1
TIME /T >> "%TEMP%\StartupLog.txt" 2>&1
ECHO An error occurred during startup. ERRORLEVEL = %ERRORLEVEL% >> "%TEMP%\StartupLog.txt" 2>&1
EXIT %ERRORLEVEL%

Add firewall rules

In Azure, there are effectively two firewalls. The first firewall controls connections between the virtual machine and the outside world. The EndPoints element in the ServiceDefinition.csdef file controls this firewall.

The second firewall controls connections between the virtual machine and the processes within that virtual machine. You can control this firewall from the netsh advfirewall firewall command-line tool.

Azure creates firewall rules for the processes started within your roles. For example, when you start a service or program, Azure automatically creates the necessary firewall rules to allow that service to communicate with the Internet. However, if you create a service started by a process outside your role (like a COM+ service or a Windows Scheduled Task), you need to manually create a firewall rule to allow access to that service. These firewall rules can be created by using a startup task.

A startup task that creates a firewall rule must have an executionContext of elevated. Add the following startup task to the ServiceDefinition.csdef file.

<ServiceDefinition name="MyService" xmlns="http://schemas.microsoft.com/ServiceHosting/2008/10/ServiceDefinition">
    <WorkerRole name="WorkerRole1">
        ...
        <Startup>
            <Task commandLine="AddFirewallRules.cmd" executionContext="elevated" taskType="simple" />
        </Startup>
    </WorkerRole>
</ServiceDefinition>

To add the firewall rule, you must use the appropriate netsh advfirewall firewall commands in your startup batch file. In this example, the startup task requires security and encryption for Transmission Control Protocol (TCP) port 80.

REM   Add a firewall rule in a startup task.

REM   Add an inbound rule requiring security and encryption for TCP port 80 traffic.
netsh advfirewall firewall add rule name="Require Encryption for Inbound TCP/80" protocol=TCP dir=in localport=80 security=authdynenc action=allow >> "%TEMP%\StartupLog.txt" 2>&1

REM   If an error occurred, return the errorlevel.
EXIT /B %errorlevel%

Block a specific IP address

You can restrict an Azure web role access to a set of specified IP addresses by modifying your IIS web.config file. You also need to use a command file that unlocks the ipSecurity section of the ApplicationHost.config file.

To do unlock the ipSecurity section of the ApplicationHost.config file, create a command file that runs at role start. Create a folder at the root level of your web role called startup and, within this folder, create a batch file called startup.cmd. Add this file to your Visual Studio project and set the properties to Copy Always to ensure you include it in your package.

Add the following startup task to the ServiceDefinition.csdef file.

<ServiceDefinition name="MyService" xmlns="http://schemas.microsoft.com/ServiceHosting/2008/10/ServiceDefinition">
    <WebRole name="WebRole1">
        ...
        <Startup>
            <Task commandLine="startup.cmd" executionContext="elevated" />
        </Startup>
    </WebRole>
</ServiceDefinition>

Add this command to the startup.cmd file:

@echo off
@echo Installing "IPv4 Address and Domain Restrictions" feature 
powershell -ExecutionPolicy Unrestricted -command "Install-WindowsFeature Web-IP-Security"
@echo Unlocking configuration for "IPv4 Address and Domain Restrictions" feature 
%windir%\system32\inetsrv\AppCmd.exe unlock config -section:system.webServer/security/ipSecurity

This task causes the startup.cmd batch file to be run every time the web role is initialized, ensuring that the required ipSecurity section is unlocked.

Finally, modify the system.webServer section your web role’s web.config file to add a list of IP addresses that are granted access, as shown in the following example:

This sample config allows all IPs to access the server except the two defined

<system.webServer>
    <security>
    <!--Unlisted IP addresses are granted access-->
    <ipSecurity>
        <!--The following IP addresses are denied access-->
        <add allowed="false" ipAddress="192.168.100.1" subnetMask="255.255.0.0" />
        <add allowed="false" ipAddress="192.168.100.2" subnetMask="255.255.0.0" />
    </ipSecurity>
    </security>
</system.webServer>

This sample config denies all IPs from accessing the server except for the two defined.

<system.webServer>
    <security>
    <!--Unlisted IP addresses are denied access-->
    <ipSecurity allowUnlisted="false">
        <!--The following IP addresses are granted access-->
        <add allowed="true" ipAddress="192.168.100.1" subnetMask="255.255.0.0" />
        <add allowed="true" ipAddress="192.168.100.2" subnetMask="255.255.0.0" />
    </ipSecurity>
    </security>
</system.webServer>

Create a PowerShell startup task

Windows PowerShell scripts can't be called directly from the ServiceDefinition.csdef file, but they can be invoked from within a startup batch file.

PowerShell (by default) doesn't run unsigned scripts. Unless you sign your script, you need to configure PowerShell to run unsigned scripts. To run unsigned scripts, the ExecutionPolicy must be set to Unrestricted. The ExecutionPolicy setting that you use is based on the version of Windows PowerShell.

REM   Run an unsigned PowerShell script and log the output
PowerShell -ExecutionPolicy Unrestricted .\startup.ps1 >> "%TEMP%\StartupLog.txt" 2>&1

REM   If an error occurred, return the errorlevel.
EXIT /B %errorlevel%

If you're using a Guest OS that is runs PowerShell 2.0 or 1.0 you can force version 2 to run, and if unavailable, use version 1.

REM   Attempt to set the execution policy by using PowerShell version 2.0 syntax.
PowerShell -Version 2.0 -ExecutionPolicy Unrestricted .\startup.ps1 >> "%TEMP%\StartupLog.txt" 2>&1

REM   If PowerShell version 2.0 isn't available. Set the execution policy by using the PowerShell
IF %ERRORLEVEL% EQU -393216 (
   PowerShell -Command "Set-ExecutionPolicy Unrestricted" >> "%TEMP%\StartupLog.txt" 2>&1
   PowerShell .\startup.ps1 >> "%TEMP%\StartupLog.txt" 2>&1
)

REM   If an error occurred, return the errorlevel.
EXIT /B %errorlevel%

Create files in local storage from a startup task

You can use a local storage resource to store files created by your startup task that your application later accesses.

To create the local storage resource, add a LocalResources section to the ServiceDefinition.csdef file and then add the LocalStorage child element. Give the local storage resource a unique name and an appropriate size for your startup task.

To use a local storage resource in your startup task, you need to create an environment variable to reference the local storage resource location. Then the startup task and the application are able to read and write files to the local storage resource.

The relevant sections of the ServiceDefinition.csdef file are shown here:

<ServiceDefinition name="MyService" xmlns="http://schemas.microsoft.com/ServiceHosting/2008/10/ServiceDefinition">
  <WorkerRole name="WorkerRole1">
    ...

    <LocalResources>
      <LocalStorage name="StartupLocalStorage" sizeInMB="5"/>
    </LocalResources>

    <Startup>
      <Task commandLine="Startup.cmd" executionContext="limited" taskType="simple">
        <Environment>
          <Variable name="PathToStartupStorage">
            <RoleInstanceValue xpath="/RoleEnvironment/CurrentInstance/LocalResources/LocalResource[@name='StartupLocalStorage']/@path" />
          </Variable>
        </Environment>
      </Task>
    </Startup>
  </WorkerRole>
</ServiceDefinition>

As an example, this Startup.cmd batch file uses the PathToStartupStorage environment variable to create the file MyTest.txt on the local storage location.

REM   Create a simple text file.

ECHO This text will go into the MyTest.txt file which will be in the    >  "%PathToStartupStorage%\MyTest.txt"
ECHO path pointed to by the PathToStartupStorage environment variable.  >> "%PathToStartupStorage%\MyTest.txt"
ECHO The contents of the PathToStartupStorage environment variable is   >> "%PathToStartupStorage%\MyTest.txt"
ECHO "%PathToStartupStorage%".                                          >> "%PathToStartupStorage%\MyTest.txt"

REM   Exit the batch file with ERRORLEVEL 0.

EXIT /b 0

You can access local storage folder from the Azure SDK by using the GetLocalResource method.

string localStoragePath = Microsoft.WindowsAzure.ServiceRuntime.RoleEnvironment.GetLocalResource("StartupLocalStorage").RootPath;

string fileContent = System.IO.File.ReadAllText(System.IO.Path.Combine(localStoragePath, "MyTestFile.txt"));

Run in the emulator or cloud

You can have your startup task perform different steps when it's operating in the cloud compared to when it is in the compute emulator. For example, you may want to use a fresh copy of your SQL data only when running in the emulator. Or you may want to do some performance optimizations for the cloud that you don't need to do when running in the emulator.

This ability to perform different actions on the compute emulator and the cloud can be accomplished by creating an environment variable in the ServiceDefinition.csdef file. You then test that environment variable for a value in your startup task.

To create the environment variable, add the Variable/RoleInstanceValue element and create an XPath value of /RoleEnvironment/Deployment/@emulated. The value of the %ComputeEmulatorRunning% environment variable is true when running on the compute emulator, and false when running on the cloud.

<ServiceDefinition name="MyService" xmlns="http://schemas.microsoft.com/ServiceHosting/2008/10/ServiceDefinition">
  <WorkerRole name="WorkerRole1">

    ...

    <Startup>
      <Task commandLine="Startup.cmd" executionContext="limited" taskType="simple">
        <Environment>
          <Variable name="ComputeEmulatorRunning">
            <RoleInstanceValue xpath="/RoleEnvironment/Deployment/@emulated" />
          </Variable>
        </Environment>
      </Task>
    </Startup>

  </WorkerRole>
</ServiceDefinition>

The task can now check the %ComputeEmulatorRunning% environment variable to perform different actions based on whether the role is running in the cloud or the emulator. Here's a .cmd shell script that checks for that environment variable.

REM   Check if this task is running on the compute emulator.

IF "%ComputeEmulatorRunning%" == "true" (
    REM   This task is running on the compute emulator. Perform tasks that must be run only in the compute emulator.
) ELSE (
    REM   This task is running on the cloud. Perform tasks that must be run only in the cloud.
)

Detect that your task has already run

The role may recycle without a reboot causing your startup tasks to run again. There's no flag to indicate that a task already ran on the host virtual machine (VM). You may have some tasks where it doesn't matter that they run multiple times. However, you may run into a situation where you need to prevent a task from running more than once.

The simplest way to detect that a task has already run is to create a file in the %TEMP% folder when the task is successful and look for it at the start of the task. Here's a sample cmd shell script that does that for you.

REM   If Task1_Success.txt exists, then Application 1 is already installed.
IF EXIST "%PathToApp1Install%\Task1_Success.txt" (
  ECHO Application 1 is already installed. Exiting. >> "%TEMP%\StartupLog.txt" 2>&1
  GOTO Finish
)

REM   Run your real exe task
ECHO Running XYZ >> "%TEMP%\StartupLog.txt" 2>&1
"%PathToApp1Install%\setup.exe" >> "%TEMP%\StartupLog.txt" 2>&1

IF %ERRORLEVEL% EQU 0 (
  REM   The application installed without error. Create a file to indicate that the task
  REM   does not need to be run again.

  ECHO This line will create a file to indicate that Application 1 installed correctly. > "%PathToApp1Install%\Task1_Success.txt"

) ELSE (
  REM   An error occurred. Log the error and exit with the error code.

  DATE /T >> "%TEMP%\StartupLog.txt" 2>&1
  TIME /T >> "%TEMP%\StartupLog.txt" 2>&1
  ECHO  An error occurred running task 1. Errorlevel = %ERRORLEVEL%. >> "%TEMP%\StartupLog.txt" 2>&1

  EXIT %ERRORLEVEL%
)

:Finish

REM   Exit normally.
EXIT /B 0

Task best practices

Here are some best practices you should follow when configuring task for your web or worker role.

Always log startup activities

Visual Studio doesn't provide a debugger to step through batch files, so it's good to get as much data on the operation of batch files as possible. Logging the output of batch files, both stdout and stderr, can give you important information when trying to debug and fix batch files. To log both stdout and stderr to the StartupLog.txt file in the directory pointed to by the %TEMP% environment variable, add the text >> "%TEMP%\\StartupLog.txt" 2>&1 to the end of specific lines you want to log. For example, to execute setup.exe in the %PathToApp1Install% directory: "%PathToApp1Install%\setup.exe" >> "%TEMP%\StartupLog.txt" 2>&1

To simplify your xml, you can create a wrapper cmd file that calls all of your startup tasks along with logging and ensures each child-task shares the same environment variables.

You may find it annoying though to use >> "%TEMP%\StartupLog.txt" 2>&1 on the end of each startup task. You can enforce task logging by creating a wrapper that handles logging for you. This wrapper calls the real batch file you want to run. Any output from the target batch file redirects to the Startuplog.txt file.

The following example shows how to redirect all output from a startup batch file. In this example, the ServerDefinition.csdef file creates a startup task that calls logwrap.cmd. logwrap.cmd calls Startup2.cmd, redirecting all output to %TEMP%\StartupLog.txt.

ServiceDefinition.cmd:

<Startup>
    <Task commandLine="logwrap.cmd startup2.cmd" executionContext="limited" taskType="simple" />
</Startup>

logwrap.cmd:

@ECHO OFF

REM   logwrap.cmd calls passed in batch file, redirecting all output to the StartupLog.txt log file.

ECHO [%date% %time%] == START logwrap.cmd ============================================== >> "%TEMP%\StartupLog.txt" 2>&1
ECHO [%date% %time%] Running %1 >> "%TEMP%\StartupLog.txt" 2>&1

REM   Call the child command batch file, redirecting all output to the StartupLog.txt log file.
START /B /WAIT %1 >> "%TEMP%\StartupLog.txt" 2>&1

REM   Log the completion of child command.
ECHO [%date% %time%] Done >> "%TEMP%\StartupLog.txt" 2>&1

IF %ERRORLEVEL% EQU 0 (

   REM   No errors occurred. Exit logwrap.cmd normally.
   ECHO [%date% %time%] == END logwrap.cmd ================================================ >> "%TEMP%\StartupLog.txt" 2>&1
   ECHO.  >> "%TEMP%\StartupLog.txt" 2>&1
   EXIT /B 0

) ELSE (

   REM   Log the error.
   ECHO [%date% %time%] An error occurred. The ERRORLEVEL = %ERRORLEVEL%.  >> "%TEMP%\StartupLog.txt" 2>&1
   ECHO [%date% %time%] == END logwrap.cmd ================================================ >> "%TEMP%\StartupLog.txt" 2>&1
   ECHO.  >> "%TEMP%\StartupLog.txt" 2>&1
   EXIT /B %ERRORLEVEL%

)

Startup2.cmd:

@ECHO OFF

REM   This is the batch file where the startup steps should be performed. Because of the
REM   way Startup2.cmd was called, all commands and their outputs will be stored in the
REM   StartupLog.txt file in the directory pointed to by the TEMP environment variable.

REM   If an error occurs, the following command will pass the ERRORLEVEL back to the
REM   calling batch file.

ECHO [%date% %time%] Some log information about this task
ECHO [%date% %time%] Some more log information about this task

EXIT %ERRORLEVEL%

Sample output in the StartupLog.txt file:

[Mon 10/17/2016 20:24:46.75] == START logwrap.cmd ============================================== 
[Mon 10/17/2016 20:24:46.75] Running command1.cmd 
[Mon 10/17/2016 20:24:46.77] Some log information about this task
[Mon 10/17/2016 20:24:46.77] Some more log information about this task
[Mon 10/17/2016 20:24:46.77] Done 
[Mon 10/17/2016 20:24:46.77] == END logwrap.cmd ================================================

Tip

The StartupLog.txt file is located in the C:\Resources\temp\{role identifier}\RoleTemp folder.

Set executionContext appropriately for startup tasks

Set privileges appropriately for the startup task. Sometimes startup tasks must run with elevated privileges even though the role runs with normal privileges.

The executionContext attribute sets the privilege level of the startup task. Using executionContext="limited" means the startup task has the same privilege level as the role. Using executionContext="elevated" means the startup task has administrator privileges, which allows the startup task to perform administrator tasks without giving administrator privileges to your role.

An example of a startup task that requires elevated privileges is a startup task that uses AppCmd.exe to configure IIS. AppCmd.exe requires executionContext="elevated".

Use the appropriate taskType

The taskType attribute determines the way the startup task is executed. There are three values: simple, background, and foreground. The background and foreground tasks are started asynchronously, and then the simple tasks are executed synchronously one at a time.

With simple startup tasks, you can set the order in which the tasks run by the order in which the tasks are listed in the ServiceDefinition.csdef file. If a simple task ends with a nonzero exit code, then the startup procedure stops and the role doesn't start.

The difference between background startup tasks and foreground startup tasks is that foreground tasks keep the role running until the foreground task ends. This structure means that if the foreground task hangs or crashes, the role remains unrecycled until the foreground task is forced closed. For this reason, background tasks are recommended for asynchronous startup tasks unless you need that feature of the foreground task.

End batch files with EXIT /B 0

The role only starts if the errorlevel from each of your simple startup task is zero. Not all programs set the errorlevel (exit code) correctly, so the batch file should end with an EXIT /B 0 if everything ran correctly.

A missing EXIT /B 0 at the end of a startup batch file is a common cause of roles that don't start.

Note

I've noticed that nested batch files sometimes stop responding when using the /B parameter. You may want to make sure that this problem does not happen if another batch file calls your current batch file, like if you use the log wrapper. You can omit the /B parameter in this case.

Expect startup tasks to run more than once

Not all role recycles include a reboot, but all role recycles include running all startup tasks. This design means that startup tasks must be able to run multiple times between reboots without any problems, which is discussed in the preceding section.

Use local storage to store files that must be accessed in the role

If you want to copy or create a file during your startup task that is then accessible to your role, then that file must be placed in local storage. See the preceding section.

Next steps

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