This PR adds region and instance ID

[LogProphet]

What kind of change does this PR introduce?

Feature: Adds region and instance_id to logger metadata (#627)

---

What is the current behavior?

This metadata is currently not included in logs, as described in issue #627.

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What is the new behavior?

Adds region and instance_id metadata to the logger using values from the environment:

System.get_env("REGION")
System.get_env("INSTANCE_ID")

This allows these fields to be available in log output for observability and debugging.

---

Additional context

I also considered adding a helper to make required env vars safer and more expressive:

defp require_env!(key) do
  case System.get_env(key) do
    nil -> raise "Required environment variable #{key} is not set"
    val -> val
  end
end

Which would allow replacing direct System.get_env/1 calls with:

Enum.into(
  [region: require_env!("REGION"), instance_id: require_env!("INSTANCE_ID")],
  primary_config.metadata
)

I also briefly considered defaulting to safe fallbacks in dev/test environments:

:ok =
  :logger.set_primary_config(
    :metadata,
    Enum.into(
      [
        region: System.get_env("REGION") || "unknown",
        instance_id: System.get_env("INSTANCE_ID") || "local"
      ],
      primary_config.metadata
    )
  )

But I wasn't sure if that was necessary, or if it might obscure misconfigured environments. If preferred, I’m happy to incorporate either approach. 😊

[vercel]

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