SpreadServe AMI part II

The core component in a SpreadServe deployment is the SpreadServeEngine, a headless C++ server binary that implements the Excel compatible calculation engine. The engine discovers its hostname through the win32 API using GetComputerNameExA( ComputerNameDnsFullyQualified, …). On AWS this was giving me hostnames like WIN-THU4IQNRN6F, when what I wanted was the fully qualified domain name, like ec2-54-186-184-85.us-west-2.compute.amazonaws.com. Harry Johnston helpfully advised on StackExchange that, since the host is not joined to a domain, GetComputerNameExA will only return the FQDN if I explicitly set it via Control Panel. Naturally I want to avoid manual fixes on a SpreadServe AMI so I settled on using Amazon’s EC2 instance metadata. The FQDN hostname can be discovered with an HTTP GET on this URL from any EC2 host: http://169.254.169.254/latest/meta-data/public-hostname. I built a small helper server process to query instance metadata using Tornado’s async HTTPClient and write it to the localFS, where SpreadServeEngine can read it. Result: any new SpreadServe AMI will automatically discover its public DNS.

SpreadServe AMI part I

Recently I’ve been working on building an EC2 AMI for SpreadServe, so deployment becomes a one click operation for Amazon AWS users. I ran into an interesting snag so I thought I’d capture it here. My aim was to deploy SpreadServe as a Windows Service on an AWS Windows Server 2012 R2 image, so I used pywin32‘s excellent win32service module. Here’s my github boilerplate project for a Windows Service in Python. On my AWS host my SpreadServe Windows Service was failing to start, and leaving no trace in the system or application event logs. pywin32service has a debug mode; when I tried that I got a Windows 0xc00007b error, which indicates a mix of 32 and 64 bit binaries. SpreadServe is 32 bit all the way, so something was wrong. I turned to procmon to try and figure what was failing. procmon showed that my 32 bit pythonservice.exe was loading a 64 bit python27.dll, instead of the 32 bit python27.dll that’s part of the SpreadServe install tree. The 64 bit DLL was coming from the C:\Program Files\Amazon\cfn-bootstrap directory, which is added to the standard Windows 2012 R2 image by Amazon to support CloudFormation, and is on the system path. After much experimenting I couldn’t find a way to stop Windows Service Host from using the system path, so I had to change it to replace cfn-bootstrap with SpreadServe directories. Problem solved…