Tiny runtime for fission

[tosone]

Problem

• I want to write my function freely.
• I write some complex function code and run it in Fission, cannot debug my function locally.
• Sometimes my function should use a special runtime framework, MUST build a special runtime for my function.
• Some users really donot want Fission to have any restrictions on code and framework.
• Now the builder and runtime Dockerfile has a lot of code snippets from the official or otherwise Dockerfile. It's so hard to upgrade them.

Proposed solution

Previously, functions were loaded as plugins in fission. We can completely load functions as child processes, and then the function can be decoupled from fission. We only need to complete a program similar to systemd to accept the specialize API. The environment we have already prepared can still be used. Some users really don't want Fission to have any restrictions on code and framework.

We call this application monitor. monitor accepts the specialize API, and specializes the container, at last startup the function.

• running directory

  • single file function should locate in /fission/ directory.
  • function is a directory, all of the directory files should layout in /fission/.

  The monitor runs the function, and /fission/ as working director.

• metrics

  monitor can expose the healthz and metric if needed.

• env

  monitor loads all of the env value from specialize API, start the function with the envs.

• command

  monitor loads the function start command, start function with this command.

• arguments

  Sometimes functions need specific arguments to start.

• logs

  monitor runs the function as a subprocess and collects the stdout and stderr.

• entrypoint

  entrypoint is useless.

• runtime

  We build all of the runtime docker images with language's official image and add new layer for the monitor, and the command is monitor.

[RealHarshThakur]

Hey @tosone ! Thanks for the proposal. I am wondering if this PR serves a similar goal : fission/fission#1681 .
There's a good ecosystem around building containers. So running them directly instead of introducing our own layer feels redundant. What are thoughts about it?

[tosone]

The goal is similar, but the startup time is my concern. I like the fission cold-start.