Language support:
AWS: Java, Node.js, C#, Python
Azure: JavaScript, C#, Python, PHP, Bash, Batch, PowerShell
Google: JavaScript
Google Cloud Functions seems to be based on a managed Node.js environment and is hence limited to .js (https://cloud.google.com/functions/docs/concepts/overview)
AWS and Azure support a multitude of different languages which may look like an ideal docker use case from far. Does anyone know some real facts here?