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docs(storage-resize-images): document FUNCTION_DEFAULT_REGION #3307

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docs(storage-resize-images): document FUNCTION_DEFAULT_REGION
IzaakGough Oct 27, 2026
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Merge branch 'kits' into docs/kits-resize-images-function-region
IzaakGough Oct 27, 2026
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26 changes: 13 additions & 13 deletions kits/storage-resize-images/README.md
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Expand Up @@ -95,6 +95,7 @@ loads them at deploy time and prompts for any required values that are missing.
| Field | Env var | Required | Default | Description |
| ---------------------- | ------------------------ | -------- | ---------------------- | ------------------------------------------------------------------------------------------ |
| `bucketRegion` | `BUCKET_REGION` | yes | (prompted) | Cloud Storage bucket location; also places the function |
| (none) | `FUNCTION_DEFAULT_REGION` | yes | (prompted) | Function region when `BUCKET_REGION` is empty ([details](#bucket_region-decides-where-the-function-runs)) |

@gemini-code-assist gemini-code-assist Bot Oct 27, 2026

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medium

Marking FUNCTION_DEFAULT_REGION as Required: yes and Default: (prompted) is misleading. Since it is not defined as a parameter in config.ts, the Firebase CLI will not prompt for it during a regular deploy if it is missing from .env. Additionally, it is only used as a fallback when BUCKET_REGION is empty, so it is not strictly required for the kit to function.

Suggested change
| (none) | `FUNCTION_DEFAULT_REGION` | yes | (prompted) | Function region when `BUCKET_REGION` is empty ([details](#bucket_region-decides-where-the-function-runs)) |
| (none) | <code>FUNCTION_DEFAULT_REGION</code> | no | (empty) | Function region when <code>BUCKET_REGION</code> is empty ([details](#bucket_region-decides-where-the-function-runs)) |

| `bucket` | `IMG_BUCKET` | no | default Storage bucket | Bucket to watch |
| `sizes` | `IMG_SIZES` | no | `200x200` | Comma-separated resize sizes |
| `deleteOriginal` | `DELETE_ORIGINAL_FILE` | no | `false` | Delete original after resize; omitted in code means `on_success` (see note below) |
Expand Down Expand Up @@ -282,21 +283,20 @@ places the function correctly. If you instead run `firebase deploy` with the
value still missing from `.env`, the prompt comes after discovery has already
chosen a region, so your answer only takes effect on the following deploy.

`firebase ext:migrate` also writes `FUNCTION_DEFAULT_REGION` to your `.env`,
recording where the extension's function ran. Nothing reads it: placement comes
from `BUCKET_REGION` alone, so if the two disagree your next deploy moves the
Projects created by `firebase functions:kits:install` or `firebase ext:migrate`
also require `FUNCTION_DEFAULT_REGION` in `.env`. `ext:migrate` sets it to the
region the extension's function ran in. A non-empty `BUCKET_REGION` overrides
it, so it only takes effect when `BUCKET_REGION` is empty.

With an explicit empty `BUCKET_REGION=` line in `.env`, the function deploys to
`FUNCTION_DEFAULT_REGION`, which must then match the bucket. If both are empty,
the deploy fails with `A function in region cannot listen to a bucket in
region <region>`. Omitting the `BUCKET_REGION` line is not the same as an empty
one: a non-interactive deploy fails with `In non-interactive mode but have no
value for the following environment variables: BUCKET_REGION`. Changing an
existing instance's region, through either variable, deletes and recreates the
function.

With an explicit empty `BUCKET_REGION=` line in `.env`, the function declares no
region and the Firebase CLI resolves one at deploy time: it keeps the region it
is already deployed in, and on a first deploy lands in `us-central1` unless you
set the `FIREBASE_FUNCTIONS_DEFAULT_REGION` environment variable when running
`firebase deploy`. Careful with that variable: it applies to every no-region
function in the deploy, not just this kit. Omitting the line is not the same as
an empty one: a non-interactive deploy fails with `In non-interactive mode but
have no value for the following environment variables: BUCKET_REGION`. Note that
changing an existing instance's region deletes and recreates the function.

## API surface

- **Main entry** (`@firebase-function-kits/storage-resize-images`): exports
Expand Down
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