Accessing Azure Role Environment information from NodeJS

When working on Azure, you may want to obtain information about your role environment: the current role instance name, the DeploymentID, or even whether the role instance is running or not. This can be tricky if you use NodeJS, because the RoleEnvironment class is managed .net code. In this article we'll going to explain how you can set up information on your running Azure role to be easily accessed from a NodeJS server. The trick is using environment variables and startup tasks running PowerShell as the bridge.

I've created this sample that shows everything so you can test this yourself. Basically, it contains a startup task that dumps the Azure role environment info into Environment variables and a server.js file to outputs those variables. Anyway, in the next few lines you can read a deeper explanation about how to do it.

What you need to do

This is pretty much what you have to do:

1. Create a startup task to launch a cmd script that access the Azure Role environment info.
2. Set the info in Environment variables so it can be accessed from NodeJS.
3. Obtain the values in the server.js file via the process.env objet.

So let's get into it. The cmd script looks like this:

setupenvironmentvariables.cmd

@ECHO off
%~d0
CD "%~dp0"

IF EXIST %WINDIR%\SysWow64 (
set powerShellDir=%WINDIR%\SysWow64\windowspowershell\v1.0
) ELSE (
set powerShellDir=%WINDIR%\system32\windowspowershell\v1.0
)

ECHO Setting the Environment variables..
CALL %powerShellDir%\powershell.exe -Command Set-ExecutionPolicy unrestricted
CALL %powerShellDir%\powershell.exe -Command "& .\set_azure_role_information.ps1"
ECHO Done!

ECHO Restarting IIS..
CALL iisreset
ECHO Done!

ECHO Starting the W3SVC service..
CALL NET START W3SVC
ECHO Done!

Some things to mention about this code:

• To execute an unsigned ps script in Azure you have to set the Execution Policy to Unrestricted. I'm using the Set-ExecutionPolicy command for this, but take into account that this value won't change unless you do it manually. Lito pointed me out that in PowerShell 2.0 you can use the -ExecutionPolicy command to set to unrestricted only for the current scope. But since the default WebRole template uses osFamily="1" which is Windows Server 2008 SP2 that coms with PowerShell 1.0, we will leave it this way (smarx wrote something about this as well)
• IMPORTANT: After the Environment variables are set, you need to restart IIS and restart the W3SVC so the changes take effect in the service. The W3SVC in Azure is set to Manual mode that's why it does not autostart aftet iisreset.

Now let's dig into the ps script.

setazurerole_information.ps1

[Reflection.Assembly]::LoadWithPartialName("Microsoft.WindowsAzure.ServiceRuntime")
[Environment]::SetEnvironmentVariable("RoleName", [Microsoft.WindowsAzure.ServiceRuntime.RoleEnvironment]::CurrentRoleInstance.Role.Name, "Machine") 
[Environment]::SetEnvironmentVariable("RoleInstanceID", [Microsoft.WindowsAzure.ServiceRuntime.RoleEnvironment]::CurrentRoleInstance.Id, "Machine")
[Environment]::SetEnvironmentVariable("RoleDeploymentID", [Microsoft.WindowsAzure.ServiceRuntime.RoleEnvironment]::DeploymentId, "Machine")
[Environment]::SetEnvironmentVariable("IsAvailable", [Microsoft.WindowsAzure.ServiceRuntime.RoleEnvironment]::IsAvailable, "Machine") 
[Environment]::SetEnvironmentVariable("CustomVariable", "Some value", "Machine")

What we're doing is setting some Environment variables with RoleEnvironment property values. Notice that you can also set a custom variable, if you want.

This is the Startup task that puts everything together.

ServiceDefinition.csdef

<Task commandLine="setup_environment_variables.cmd" executionContext="elevated" taskType="simple" />

And finally, below is the server.js file that writes the results in the response.

server.js

var http = require('http');
var port = process.env.port || 1337;

http.createServer(function (req, res) {
res.writeHead(200, { 'Content-Type': 'text/plain' });

res.write("Role Name: " + process.env.RoleName + "\n");
res.write("Role InstanceID: " + process.env.RoleInstanceID + "\n");
res.write("Role DeploymentID: " + process.env.RoleDeploymentID + "\n");
res.write("Is running?: " + process.env.IsAvailable + "\n");
res.write("Custom variable: " + process.env.CustomVariable + "\n");

res.end();
}).listen(port);

This is the result you get if you run the sample in the emulator: