I have a Django application deployed on Google App Engine standard environment. I am interested in server side rendering of my JS frontend. Can I use node.js alongside Django on the same GAE? Maybe as microservice?
What you can do is to deploy each of your app as a separate service in App Engine and they will work independently as a microservice. To do so, make sure to set a service name for each of the app.yaml file of your apps:
service: service-name
Afterwards, you can communicate between your services through an HTTP invocation, such as a user request or a RESTful API call. Code in one service can't directly call code in another service.
Refer to this link for additional information about communicating between your services.