Extend Pod Information to Containers Through Environment Variables specifically valueFrom

[dboschbach-bw]

Describe the current behavior

Currently the job template generation only allows to create simple key value pairs even though Kubernetes supports https://kubernetes.io/docs/tasks/inject-data-application/environment-variable-expose-pod-information/ more.
Example:

"env": {
    "PREFECT_HOME": "/home/prefect",
    "PREFECT_DEBUG_MODE": "false",
    "PREFECT_LOCAL_STORAGE_PATH": "/home/prefect/storage",
    "DD_AGENT_HOST": {
        "valueFrom": {
            "fieldRef": {"apiVersion": "v1", "fieldPath": "status.hostIP"}
        }
    }
}

Results:

env:
...
  - name: PREFECT_DEBUG_MODE
    value: 'False'
  - name: PREFECT_HOME
    value: /home/prefect
  - name: DD_AGENT_HOST
    value: '{''valueFrom'': {''fieldRef'': {''fieldPath'': ''status.hostIP'', ''apiVersion'': ''v1''}}}'
  - name: PREFECT_LOCAL_STORAGE_PATH
    value: /home/prefect/storage

Looking at the Prefect 2 code

class BaseJobConfiguration(BaseModel):
...
async def from_template_and_values (
...
if isinstance(base_config.get("env"), dict) and (
    deployment_env := variables.get("env")
):
    base_config["env"] = {**base_config.get("env", {}), **deployment_env}

or Prefect 3 code it is simply not supported yet.

async def from_template_and_values (
...
    if isinstance(job_config.get("env"), dict) and (
        hardcoded_env := variables.get("env")
    ):
        job_config["env"] = hardcoded_env | job_config.get("env")

Describe the proposed behavior

• Use Pod fields as values for environment variables
• Use container fields as values for environment variables

Example Use

Template:

"env": {
    "PREFECT_HOME": "/home/prefect",
    "PREFECT_DEBUG_MODE": "false",
    "PREFECT_LOCAL_STORAGE_PATH": "/home/prefect/storage",
    "DD_AGENT_HOST": {
        "valueFrom": {
            "fieldRef": {"apiVersion": "v1", "fieldPath": "status.hostIP"}
        }
    }
}

Result:

env:
...
  - name: PREFECT_DEBUG_MODE
    value: 'False'
  - name: PREFECT_HOME
    value: /home/prefect
  - name: DD_AGENT_HOST
    valueFrom:
      fieldRef:
        apiVersion: v1
        fieldPath: status.hostIP
  - name: PREFECT_LOCAL_STORAGE_PATH
    value: /home/prefect/storage

Additional context

No response