diff --git a/Dockerfile.compute-node b/Dockerfile.compute-node
index 7d60458a3e..2c4465fc82 100644
--- a/Dockerfile.compute-node
+++ b/Dockerfile.compute-node
@@ -774,12 +774,14 @@ RUN rm /usr/local/pgsql/lib/lib*.a
 FROM python:3.9-slim-bullseye AS generate-ext-index
 ARG PG_VERSION
 ARG BUILD_TAG
+RUN apt update && apt install -y zstd
+
 # copy the control files here
 COPY --from=kq-imcx-pg-build /extensions/ /extensions/
 COPY --from=pg-anon-pg-build /extensions/ /extensions/
 COPY --from=postgis-build /extensions/ /extensions/
 COPY scripts/combine_control_files.py ./combine_control_files.py
-RUN python3 ./combine_control_files.py ${PG_VERSION} ${BUILD_TAG}
+RUN python3 ./combine_control_files.py ${PG_VERSION} ${BUILD_TAG} --public_extensions="anon,postgis"
 
 FROM scratch AS postgres-extensions
 # After the transition this layer will include all extensitons.
diff --git a/scripts/combine_control_files.py b/scripts/combine_control_files.py
index 37db522ddd..0350e4721d 100644
--- a/scripts/combine_control_files.py
+++ b/scripts/combine_control_files.py
@@ -4,17 +4,49 @@
 # for all extensions in extensions subdir.
 import argparse
 import json
+import subprocess
 from pathlib import Path
 
+"""
+# ext_index.json example:
+{
+    "public_extensions": [
+        "anon"
+    ],
+    "library_index": {
+        "anon": "anon",
+        "kq_imcx": "kq_imcx"
+        // would be more complicated for something like postgis where multiple library names all map to postgis
+    },
+    "extension_data": {
+        "kq_imcx": {
+            "control_data": {
+                "kq_imcx.control": "# This file is generated content from add_postgresql_extension.\n# No point in modifying it, it will be overwritten anyway.\n\n# Default version, always set\ndefault_version = '0.1'\n\n# Module pathname generated from target shared library name. Use\n# MODULE_PATHNAME in script file.\nmodule_pathname = '$libdir/kq_imcx.so'\n\n# Comment for extension. Set using COMMENT option. Can be set in\n# script file as well.\ncomment = 'ketteQ In-Memory Calendar Extension (IMCX)'\n\n# Encoding for script file. Set using ENCODING option.\n#encoding = ''\n\n# Required extensions. Set using REQUIRES option (multi-valued).\n#requires = ''\ntrusted = true\n"
+            },
+            "archive_path": "5648391853/v15/extensions/kq_imcx.tar.zst"
+        },
+        "anon": {
+            "control_data": {
+                "anon.control": "# PostgreSQL Anonymizer (anon) extension \ncomment = 'Data anonymization tools' \ndefault_version = '1.1.0' \ndirectory='extension/anon' \nrelocatable = false \nrequires = 'pgcrypto' \nsuperuser = false \nmodule_pathname = '$libdir/anon' \ntrusted = true \n"
+            },
+            "archive_path": "5648391853/v15/extensions/anon.tar.zst"
+        }
+    }
+}
+"""
+
 if __name__ == "__main__":
     parser = argparse.ArgumentParser(description="generate ext_index.json")
     parser.add_argument("pg_version", type=str, choices=["v14", "v15"], help="pg_version")
     parser.add_argument("BUILD_TAG", type=str, help="BUILD_TAG for this compute image")
+    parser.add_argument("--public_extensions", type=str, help="list of public extensions")
     args = parser.parse_args()
     pg_version = args.pg_version
     BUILD_TAG = args.BUILD_TAG
+    public_ext_list = args.public_extensions.split(",")
 
     ext_index = {}
+    library_index = {}
     EXT_PATH = Path("extensions")
     for extension in EXT_PATH.iterdir():
         if extension.is_dir():
@@ -28,6 +60,21 @@ if __name__ == "__main__":
                 "control_data": control_data,
                 "archive_path": f"{BUILD_TAG}/{pg_version}/extensions/{extension.name}.tar.zst",
             }
+        elif extension.suffix == ".zst":
+            file_list = (
+                str(subprocess.check_output(["tar", "tf", str(extension)]), "utf-8")
+                .strip()
+                .split("\n")
+            )
+            for file in file_list:
+                if file.endswith(".so") and file.startswith("lib/"):
+                    lib_name = file[4:-3]
+                    library_index[lib_name] = extension.name.replace(".tar.zst", "")
 
+    all_data = {
+        "public_extensions": public_ext_list,
+        "library_index": library_index,
+        "extension_data": ext_index,
+    }
     with open("ext_index.json", "w") as f:
-        json.dump(ext_index, f)
+        json.dump(all_data, f)