prefetch container optimization

[sjfink]

To reduce cold start overhead -- if we have a good reason to believe that an action will be invoked soon -- then send a message to /init a container. I think this could be done by adding "init" messages to the kafka protocol. When receiving an "init" message, the invoker would /init a container if none is present already.

The obvious use case is sequences -- when a sequence is run, "init" all the actions in the sequence immediately.

[jbci]

Hi @sjfink,
i'd be glad to contribute to the openwhisk project and this issue seems a good starting point.
what do you think about?

[sjfink]

@jbci go for it!