Add change log for arq-related changes

Document the changes due to the arq conversion and its corresponding
Phalanx chart changes. Add a pointer to the change log to README.md.

CHANGELOG.md

@@ -1,7 +1,6 @@
 # Change log
 
-vo-cutouts is versioned with [semver](https://semver.org/).
-Dependencies are updated to the latest available version during each release, and aren't noted here.
+vo-cutouts is versioned with [semver](https://semver.org/). Dependencies are updated to the latest available version during each release, and aren't noted here.
 
 Find changes for the upcoming release in the project's [changelog.d directory](https://github.com/lsst-sqre/vo-cutouts/tree/main/changelog.d/).
 

README.md

@@ -3,6 +3,8 @@
 vo-cutouts is a [FastAPI](https://fastapi.tiangolo.com/) web service and associated backend worker implementation that implements an image cutout service for the Rubin Science Platform.
 The underlying work of generating the cutout is delegated to [lsst.image_cutout_backend](https://github.com/lsst-dm/image_cutout_backend/).
 
+See [CHANGELOG.md](https://github.com/lsst-sqre/vo-cutouts/blob/main/CHANGELOG.md) for the change history of vo-cutouts.
+
 This is the concrete implementation of the architecture in [DMTN-139](https://dmtn-139.lsst.io/) (not yet published) and the design in [DMTN-208](https://dmtn-208.lsst.io/).
 
 vo-cutouts implements the image cutout portion of the IVOA [SODA](https://ivoa.net/documents/SODA/20170517/REC-SODA-1.0.html) specification.

changelog.d/20240606_103703_rra_DM_44606.md

@@ -0,0 +1,12 @@
+### Backwards-incompatible changes
+
+- Change the job queuing system from Dramatiq to [arq](https://arq-docs.helpmanual.io/). This change should be transparent to users when creating new jobs, but any in-progress jobs at the time of the upgrade will be orphaned.
+- Use workload identity for all authentication when deployed on Google Cloud. Separate service account keys are no longer required or used. The `vo-cutouts` Google service account now requires the `storage.legacyBucketWriter` role in addition to `storage.objectViewer`.
+
+### New features
+
+- Add support for `gs` storage URLs in addition to `s3` storage URLs. When a `gs` storage URL is used, the image cutout backend will use the Google Cloud Storage Python API to store the results instead of boto, which will work correctly with workload identity.
+
+### Bug fixes
+
+- Queuing a job for execution in the frontend is now async and will not block the event loop, which may help with performance under load.