Launch Configuration

This post is part of a bigger topic Autoscaling Publishers in AWS.

Each Auto Scaling Group in AWS is based on a Launch Configuration. The Launch Configuration cannot be modified once it's created, but it can however be copied and modified.

Once Auto Scaling is in place, the instances it creates will all be based on the specified Launch Configuration.

Creating a Launch Configuration implies specifying the AMI, the Instance Type, Security IAM role, EBS drive, security group and open incoming ports. All these are AWS settings and they don't make the object of this post.

What is particularly interesting is the section Configure details, subsection User data. This is where one can specify either a script of a file containing a script that will be executed inside the instance once it is created and it starts. Using this mechanism we created PowerShell scripts to configure each Publisher instance in part.

<powershell>
aws s3 cp s3://mybucket/scripts/publisher_userdata.ps1 D:\scripts\publisher_userdata.ps1
D:\scripts\publisher_userdata.ps1 2>&1 > D:\userdata.log
</powershell>

The implementation we used here is to copy a PowerShell script from an S3 bucket into the instance; then, execute the script inside the instance. This approach is flexible in the sense that one doesn't have to recreate the Launch Configuration in order to make modifications to the user data script.

The highlights of the script below show how the instance is configured. First the DNS is set on the server. Then a series of scripts are copied from S3 bucket to the local harddisk. The same mechanism is used to copy patches (jars, dlls, config files) when needed, without having to recreate the AMI.

The downloaded scripts are going to be executed on a subsequent reboot of the machine. During this initial execution, the machine is renamed to the name that has been extracted from the license server, but more about that in the following post.

$Logfile = "D:\tst.log"
Function LogWrite {
   Param ([string]$logstring)
   Add-content $Logfile -value $logstring
}
LogWrite("Start script...")

$message=""
function setDNS($DNSServers) {
    try {
  $NICs = Get-WMIObject Win32_NetworkAdapterConfiguration |where{$_.IPEnabled -eq "TRUE"}
  Foreach($NIC in $NICs) {
   $message += $NIC.SetDNSServerSearchOrder(@($DNSServers)) | Out-String
  }
 } catch {}
}
setDNS($DNSServers)
echo "DNS settings done"
LogWrite("DNS changed.")

LogWrite("downloading resume scripts")
Rename-Item "D:\SDL Web\lib\cd_transport.jar" cd_transport.jar_old
aws s3 cp s3://mybucket/jar/cd_transport-8.5.0-1050.jar "D:\SDL Web\lib\cd_transport-8.5.0-1050.jar"
aws s3 cp s3://mybucket/scripts/resume-workflows.ps1 d:\scripts\resume-workflows.ps1
aws s3 cp s3://mybucket/scripts/resume-workflows.cmd d:\scripts\resume-workflows.cmd
aws s3 cp s3://mybucket/scripts/resume_powershell_workflows.xml d:\scripts\resume_powershell_workflows.xml
aws s3 cp s3://mybucket/scripts/join_ad.ps1 d:\scripts\join_ad.ps1
aws s3 cp s3://mybucket/scripts/cleanup.ps1 d:\scripts\cleanup.ps1
aws s3 cp s3://mybucket/scripts/dns.ps1 d:\scripts\dns.ps1
aws s3 cp s3://mybucket/scripts/run-change-dns.cmd d:\scripts\run-change-dns.cmd
aws s3 cp s3://mybucket/config/cd_transport_conf.xml "D:\SDL Web\config\cd_transport_conf.xml"
aws s3 cp s3://mybucket/config/Tridion.ContentManager.config "D:\SDL Web\config\Tridion.ContentManager.config"

LogWrite("Creating scheduled task")
SchTasks /Create /SC ONSTART /RL HIGHEST /RU SYSTEM /TN "Resume Powershell Workflows" /TR "d:\scripts\resume-workflows.cmd"

LogWrite("Renaming & Rebooting...")
Rename-Computer -NewName $license_hostname -Force -Restart