XFN Runner: Show STDOUT of failed composition function (exit code >= 1)

[jan-di]

What problem are you facing?

We've implemented a function similar to the example functions from docs. If this functions fails, it returns a exit code greater than 0 and prints the error message in STDOUT.

[..] "error": "cannot run Composition Function pipeline: cannot run function \"service-versioning\": cannot run container: rpc error: code = Unknown desc = exit status 1: xfn: error: spark.Command.Run(): OCI runtime error: exit status 1"

Currenty, I cannot debug a composition function that fails to execute. When the function in the OCI container fails, I see the exit code but no additional information printed in STDOUT.

How could Crossplane help solve your problem?

Provide a way to see the STDOUT of functions that failed. That may be behind a flag/option like verbosity level/debug mode, etc.
Perhaps, also STDERR could be used, as it would be the more appropriate place for error messages.

[negz]

The xfn runner has moved out-of-tree, so I'm moving this issue. In v1.14 (due end of the month) we'll have a new architecture for Functions that won't be prone to this issue. We haven't started on docs yet for the new architecture, but you can learn about it here:

• Try out beta Composition Functions! crossplane#4639
• https://github.com/crossplane/crossplane/blob/579702/design/design-doc-composition-functions.md

[jan-di]

That sounds really good, thanks!

If others stumble upon this thing, we worked around it by sending the uncatched exceptions to a HTTP endpoint (jmalloc/echo-server) that runs in the same cluster. It's absolutely not pretty, but get's the job done.

import http.client
import sys
import traceback

def main():
    try:
        # your actual function code
    except Exception as e:
        try:
            trace = traceback.format_exc()
            host = "echo.default.svc.cluster.local"
            conn = http.client.HTTPConnection(host, 80)
            conn.request("POST", "/", headers={"Host": host}, body=str(trace))
            response = conn.getresponse()
            if response.status >= 400 or response.status < 200:
                raise Exception("webtrace failed")
            sys.exit(90)
        except:
            sys.exit(99)

        raise e