SpreadServe AMI part II

January 17, 2017

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.

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