Add New ExecOutput Function To Support Custom Writers

[ihcsim]

Change Overview

This PR introduces a new kube.ExecOutput() library function that can write kube.Exec() outputs to custom writers, allowing callers to provide either buffered writers or async (pipe) writers. This new function delegates the writes operation to a new format.Writer instance that formats the outputs to match the Kanister-style logs, before writing them to the custom writers.

The KubeExec Kanister function has been updated to use kube.ExecOutput(), with os.Stdout and os.Stderr. Other callers in the pkg/app and pkg/function packages remain untouched. By offering both kube.Exec() and kube.ExecAsync(), downstream has the flexibility to decide which output mechanism to use, based on their use cases.

Pull request type

Please check the type of change your PR introduces:

• 🚧 Work in Progress
• 🌈 Refactoring (no functional changes, no api changes)
• 🐹 Trivial/Minor
• 🐛 Bugfix
• 🌻 Feature
• 🗺️ Documentation
• 🤖 Test

Issues

Follow-up of:

• Stream output from KubeExec #1194
• Stream output from KubeExec #1037

Test Plan

Deploy this timer pod that has a script to tail the current datetime at one second interval:

cat <<EOF | k apply -f -
apiVersion: v1
kind: Pod
metadata:
  name: timer
spec:
  containers:
  - name: timer
    image: ubuntu
    command:
    - /bin/sh
    - "-c"
    - |
      cat <<EOF > /bin/tail_datetime.sh
      for i in \\\$(seq 0 20)
      do
        date +"%m-%d-%Y %H:%M:%S"
        sleep 1s
      done
      EOF

      chmod +x /bin/tail_datetime.sh
      sleep 7200s
EOF

Deploy this blueprint that uses KubeExec to invoke the remote script in the timer pod:

cat <<EOF | k apply -f -
apiVersion: cr.kanister.io/v1alpha1
kind: Blueprint
metadata:
  name: timer
  namespace: kanister
actions:
  tail:
    phases:
    - func: KubeExec
      name: tail
      args:
        namespace: default
        pod: timer
        container: timer
        command:
        - sh
        - "-c"
        - /bin/tail_datetime.sh
EOF

Creates the actionset to trigger the function call:

cat <<EOF | k create -f -
apiVersion: cr.kanister.io/v1alpha1
kind: ActionSet
metadata:
  generateName: timer-
  namespace: kanister
spec:
  actions:
  - name: tail
    blueprint: timer
    object:
      kind: Namespace
      name: default
EOF

Observe the datetime being streamed to the Kanister operator's logs:

$ k -n kanister logs -f kanister-kanister-operator-5964486449-xqv66
#...

{"Container":"timer","File":"pkg/log/log.go","Function":"github.com/kanisterio/kanister/pkg/log.PrintTo","Line":174,"Out":"03-25-2022 05:52:49","Pod":"timer","cluster_name":"8224a31e-876b-4ef2-98c2-ae9cbc5e96b0","hostname":"kanister-kanister-operator-5964486449-xqv66","level":"info","msg":"action update","time":"2022-03-25T05:52:49.060833604Z"}
{"Container":"timer","File":"pkg/log/log.go","Function":"github.com/kanisterio/kanister/pkg/log.PrintTo","Line":174,"Out":"03-25-2022 05:52:50","Pod":"timer","cluster_name":"8224a31e-876b-4ef2-98c2-ae9cbc5e96b0","hostname":"kanister-kanister-operator-5964486449-xqv66","level":"info","msg":"action update","time":"2022-03-25T05:52:50.063202873Z"}
{"ActionSet":"timer-2pkxw","File":"pkg/controller/controller.go","Function":"github.com/kanisterio/kanister/pkg/controller.(*Controller).logAndSuccessEvent","Line":510,"Phase":"tail","cluster_name":"8224a31e-876b-4ef2-98c2-ae9cbc5e96b0","hostname":"kanister-kanister-operator-5964486449-xqv66","level":"info","msg":"Completed phase tail","time":"2022-03-25T05:52:51.077562462Z"}
{"File":"pkg/controller/controller.go","Function":"github.com/kanisterio/kanister/pkg/controller.(*Controller).logAndSuccessEvent","Line":510,"cluster_name":"8224a31e-876b-4ef2-98c2-ae9cbc5e96b0","hostname":"kanister-kanister-operator-5964486449-xqv66","level":"info","msg":"Updated ActionSet 'timer-2pkxw' Status-\u003ecomplete","time":"2022-03-25T05:52:51.081930515Z"}

• 💪 Manual
• ⚡ Unit test
• 💚 E2E

[pavannd1]

LGTM