Document system-level environment variables configs (#3243)

Signed-off-by: shalberd <[email protected]>

docs/source/index.rst

@@ -51,6 +51,7 @@ Elyra is a set of AI-centric extensions to JupyterLab Notebooks.
    user_guide/pipeline-components.md
    user_guide/best-practices-custom-pipeline-components
    user_guide/best-practices-file-based-nodes.md
+   user_guide/env-variables-file-based-nodes.md
    user_guide/enhanced-script-support.md
    user_guide/code-snippets.md
 

docs/source/user_guide/env-variables-file-based-nodes.md

@@ -0,0 +1,65 @@
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+Copyright 2018-2023 Elyra Authors
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+-->
+## System-level environment variables used in file-based pipeline nodes
+
+[Generic pipelines and typed pipelines](pipelines.md) support natively file-based nodes for  Jupyter notebooks, Python scripts, and R scripts. In order to support heterogeneous execution - that is making them runnable to your requiremenents in any runtime environment (JupyterLab, Kubeflow Pipelines, and Apache Airflow) - follow the documentation on environment variables listed below.
+
+There are system-level environment variables for two types of scopes:
+- Jupyterlab pipeline generation and validation (PipelineProcessor)
+- Runtime image task (Airflow) or component (KFP) execution of file-based node Jupyter notebooks, Python scripts, and R scripts (bootstrapper pipeline run)
+
+This page lists the environment variables; their scope, defaults, and background concept.
+
+### `ELYRA_ENABLE_PIPELINE_INFO`
+
+Scope: Jupyterlab PipelineProcessor and runtime image task execution in runtime environment
+Impact: Produces a formatted log INFO message used entirely for support purposes.
+Having single-line entries in the log (no embedded newlines) with pipeline name, operation_name, action and Duration makes it easy to cross-evaluate logs across log files.
+
+Background: During processing of Pipelines in jupyterlab, i.e. before execution when logging pipeline info during submitting the pipeline, processing later Pipeline operation dependencies,
+submitting the Pipeline to Git, and exporting the Pipeline as KFP Python or yaml or Airflow DAG Python code (not needed with local / LocalPipelineProcessor).
+
+Also used in runtime-specific container environment in bootstrapper.py python code for execution run logging operation info of KFP Pipeline components and Airflow Pipeline / DAG Tasks to
+log KFP component / Airflow task execution info when execution of the script starts, dependencies are processed, and the script execution operation ends.
+
+Default: We recommend leaving this at its default "true", i.e. no explicit setting of this environment variable necessary.
+If you want to set `ELYRA_ENABLE_PIPELINE_INFO` to `false`, you can do so in either
+- Jupyterlab at runtime
+- Statically baked into Jupyterlab container definition for use in Jupyterlab container build
+- Pipeline Editor at Pipeline Properties - Generic Node Defaults - Environment Variables or at Node Properties - Additional Properties - Environment Variables
+- Statically baked into Jupyterlab container definition for use in KFP or Airflow runtime image container build
+
+### `ELYRA_GENERIC_NODES_ENABLE_SCRIPT_OUTPUT_TO_S3`
+
+Scope: Runtime image task (Airflow) or component (KFP) execution of file-based node Jupyter notebooks, Python scripts, and R scripts (bootstrapper pipeline run). Relevant for pipeline runs in KFP components or Airflow DAGs.
+Background:
+- Puts script execution Output / STDOUT into a .log file for Python and R Scripts. 
+- Puts script execution Output / STDOUT into a notebookname-output.ipynb and notebookname-Output.html file.
+
+Impact: Controls whether the files are then uploaded to the Elyra S3 bucket, if this environment variable is not set at pipeline, node, or runtime container level.
+
+Default: `true` if not specified, i.e. no explicit setting of this environment variable necessary.
+
+Background: 
+If you prefer to use S3-compatible storage for transfer of files between pipeline steps only and **not for logging information / run output of R, Python and Jupyter Notebook files**,
+for example because you capture and store logs with central KFP, Airflow, K8S / Openshift mechanisms,
+set env var **`ELYRA_GENERIC_NODES_ENABLE_SCRIPT_OUTPUT_TO_S3`** to **`false`**.
+
+If you want to set `ELYRA_GENERIC_NODES_ENABLE_SCRIPT_OUTPUT_TO_S3` to `false`, you can do so in either
+- Pipeline Editor at Pipeline Properties - Generic Node Defaults - Environment Variables or at Node Properties - Additional Properties - Environment Variables
+- Statically baked into Jupyterlab container definition for use in KFP or Airflow runtime image container build