diff --git a/.github/workflows/build-manually.yaml b/.github/workflows/build-manually.yaml
index cbad7f3..22381ec 100644
--- a/.github/workflows/build-manually.yaml
+++ b/.github/workflows/build-manually.yaml
@@ -5,11 +5,11 @@ on:
       rubinenvVersion:
         description: 'rubin-env version'
         required: true
-        default: '7.0.1'
+        default: '8.0.0'
       obsLsstVersion:
         description: 'Science Pipelines release'
         required: true
-        default: 'w_2023_41'
+        default: 'w_2024_12'
 
 
 env:
diff --git a/.github/workflows/build.yaml b/.github/workflows/build.yaml
index aa127bf..32f164f 100644
--- a/.github/workflows/build.yaml
+++ b/.github/workflows/build.yaml
@@ -11,6 +11,7 @@ env:
   ENQUEUE_NAME: embargo-butler-enqueue
   INGEST_NAME: embargo-butler-ingest
   IDLE_NAME: embargo-butler-idle
+  PRESENCE_NAME: embargo-butler-presence
 
 jobs:
   push:
@@ -20,7 +21,7 @@ jobs:
       contents: read
     steps:
     - name: Checkout
-      uses: actions/checkout@v3
+      uses: actions/checkout@v4
 
     - name: Build enqueue image
       run: |
@@ -43,6 +44,13 @@ jobs:
           --tag $IDLE_NAME \
           --label "runnumber=${GITHUB_RUN_ID}"
 
+    - name: Build presence image
+      run: |
+        docker build . \
+          -f Dockerfile.presence \
+          --tag $PRESENCE_NAME \
+          --label "runnumber=${GITHUB_RUN_ID}"
+
     - name: Log in to GitHub Container Registry
       run: echo "${{ secrets.GITHUB_TOKEN }}" | docker login ghcr.io -u $ --password-stdin
 
@@ -51,6 +59,7 @@ jobs:
         ENQUEUE_ID=ghcr.io/${{ github.repository_owner }}/$ENQUEUE_NAME
         INGEST_ID=ghcr.io/${{ github.repository_owner }}/$INGEST_NAME
         IDLE_ID=ghcr.io/${{ github.repository_owner }}/$IDLE_NAME
+        PRESENCE_ID=ghcr.io/${{ github.repository_owner }}/$PRESENCE_NAME
 
         if [[ "${{ github.ref }}" == "refs/pull/"* ]]; then
           VERSION=$(echo "${{ github.head_ref }}" | sed -e 's|.*/||')
@@ -62,6 +71,7 @@ jobs:
         echo ENQUEUE_ID=$ENQUEUE_ID
         echo INGEST_ID=$INGEST_ID
         echo IDLE_ID=$IDLE_ID
+        echo PRESENCE_ID=$PRESENCE_ID
         echo VERSION=$VERSION
         docker tag $ENQUEUE_NAME $ENQUEUE_ID:$VERSION
         docker push $ENQUEUE_ID:$VERSION
@@ -69,3 +79,5 @@ jobs:
         docker push $INGEST_ID:$VERSION
         docker tag $IDLE_NAME $IDLE_ID:$VERSION
         docker push $IDLE_ID:$VERSION
+        docker tag $PRESENCE_NAME $PRESENCE_ID:$VERSION
+        docker push $PRESENCE_ID:$VERSION
diff --git a/Dockerfile.presence b/Dockerfile.presence
new file mode 100644
index 0000000..23ff0c7
--- /dev/null
+++ b/Dockerfile.presence
@@ -0,0 +1,32 @@
+# This file is part of embargo_butler.
+#
+# Developed for the LSST Data Management System.
+# This product includes software developed by the LSST Project
+# (http://www.lsst.org).
+# See the COPYRIGHT file at the top-level directory of this distribution
+# for details of code ownership.
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# Dockerfile for presence service.
+
+FROM python:3.11
+RUN pip install redis gunicorn flask
+WORKDIR /presence
+COPY src/presence.py src/utils.py /presence/
+# environment variables that must be set:
+# REDIS_HOST REDIS_PASSWORD
+# optional:
+# DELETE_SEEN
+ENTRYPOINT [ "gunicorn", "-b", "0.0.0.0:8000", "-w", "2", "presence:app" ]
diff --git a/src/ingest.py b/src/ingest.py
index 08a4896..42a1d93 100644
--- a/src/ingest.py
+++ b/src/ingest.py
@@ -22,10 +22,12 @@
 """
 Service to ingest images or LFA objects into per-bucket Butler repos.
 """
+import json
 import os
 import socket
 import time
 
+import astropy.io.fits
 import requests
 from lsst.daf.butler import Butler
 from lsst.obs.base import DefineVisitsTask, RawIngestTask
@@ -50,6 +52,7 @@
 butler_repo = os.environ["BUTLER_REPO"]
 webhook_uri = os.environ.get("WEBHOOK_URI", None)
 is_lfa = "rubinobs-lfa-" in bucket
+group_lifetime = int(os.environ.get("GROUP_LIFETIME", 86400))
 
 worker_name = socket.gethostname()
 worker_queue = f"WORKER:{bucket}:{worker_name}"
@@ -134,6 +137,44 @@ def on_metadata_failure(dataset, exc):
         pipe.execute()
 
 
+def record_groups(resources: list[ResourcePath]) -> None:
+    """Record the group ids from received FITS files in Redis.
+
+    Parameters
+    ----------
+    resources: `list` [`ResourcePath`]
+        The resources to record group ids from.
+    """
+
+    global r, group_lifetime, logger
+    with r.pipeline() as pipe:
+        for res in resources:
+            if not res.exists():
+                continue
+            json_file = res.updatedExtension("json")
+            header = {}
+            try:
+                with json_file.open("rb") as f:
+                    header = json.load(f)
+            except Exception:
+                try:
+                    with res.open("rb") as f:
+                        header = astropy.io.fits.open(f)[0].header
+                except Exception:
+                    logger.exception("Error reading header for %s", res)
+            try:
+                instrument = header["INSTRUME"]
+                groupid = header["GROUPID"]
+                snap_number = int(header["CURINDEX"]) - 1
+                detector = header["RAFTBAY"] + "_" + header["CCDSLOT"]
+                key = f"GROUP:{instrument}:{groupid}:{snap_number}:{detector}"
+                pipe.set(key, str(res))
+                pipe.expire(key, group_lifetime)
+            except Exception:
+                logger.exception("Error reading group for %s", res)
+        pipe.execute()
+
+
 def main():
     """Ingest FITS files from a Redis queue."""
     logger.info("Initializing Butler from %s", butler_repo)
@@ -162,12 +203,17 @@ def main():
 
             # Ingest if we have resources
             if resources:
+
+                if not is_lfa:
+                    record_groups(resources)
+
                 logger.info("Ingesting %s", resources)
                 refs = None
                 try:
                     refs = ingester.run(resources)
                 except Exception:
                     logger.exception("Error while ingesting %s", resources)
+                    continue
 
                 # Define visits if we ingested anything
                 if not is_lfa and refs:
diff --git a/src/presence.py b/src/presence.py
new file mode 100644
index 0000000..77607e0
--- /dev/null
+++ b/src/presence.py
@@ -0,0 +1,78 @@
+# This file is part of embargo_butler.
+#
+# Developed for the LSST Data Management System.
+# This product includes software developed by the LSST Project
+# (http://www.lsst.org).
+# See the COPYRIGHT file at the top-level directory of this distribution
+# for details of code ownership.
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+"""
+Presence service to translate group names to image URIs.
+"""
+import os
+import re
+
+from flask import Flask
+
+from utils import setup_logging, setup_redis
+
+logger = setup_logging(__name__)
+r = setup_redis()
+
+# Delete image key when seen, before it expires, to save space
+delete_seen = os.environ.get("DELETE_SEEN") is not None
+
+app = Flask(__name__)
+
+
+@app.get("/presence/<instrument>/<group_name>/<int:snap_index>/<detector_name>")
+def presence(instrument: str, group_name: str, snap_index: int, detector_name: str) -> dict | tuple:
+    """Return the presence and URI of an image matching the parameters.
+
+    Parameters
+    ----------
+    instrument: `str`
+        Name of the instrument taking the image.
+    group_name: `str`
+        Name of the group (from the GROUPID FITS header).
+    snap_index: `int`
+        Number of the snap (zero-based).
+    detector_name: `str`
+        Name of the detector ("RNN_SNN").
+
+    Returns
+    -------
+    json: `dict`
+        JSON with "error", "present", "uri", and/or "message" keys.
+    """
+
+    try:
+        if instrument not in ("LATISS", "LSSTComCam", "LSSTComCamSim", "LSSTCam", "LSST-TS8"):
+            return ({"error": True, "message": f"Unknown instrument {instrument}"}, 400)
+        if not re.match(r"R\d\d_S\d\d", detector_name):
+            return ({"error": True, "message": f"Unrecognized detector name {detector_name}"}, 400)
+        key = f"GROUP:{instrument}:{group_name}:{snap_index}:{detector_name}"
+        result = r.get(key)
+        if result:
+            logger.info(f"Found key {key}")
+            if delete_seen:
+                r.delete(key)
+            return {"error": False, "present": True, "uri": result.decode()}
+        else:
+            logger.debug(f"No key {key}")
+            return {"error": False, "present": False}
+    except Exception as e:
+        return ({"error": True, "message": str(e)}, 500)