diff --git a/global/overlay/etc/puppet/setup_cosmos_modules b/global/overlay/etc/puppet/setup_cosmos_modules
new file mode 100644
index 0000000..aa910ef
--- /dev/null
+++ b/global/overlay/etc/puppet/setup_cosmos_modules
@@ -0,0 +1,148 @@
+#!/usr/bin/env python3
+""" Write out a puppet cosmos-modules.conf """
+
+import hashlib
+import os
+import os.path
+import socket
+import sys
+
+try:
+    from configobj import ConfigObj
+    os_info = ConfigObj("/etc/os-release")
+except (IOError, ModuleNotFoundError):
+    os_info = None
+
+try:
+    fqdn = socket.getfqdn()
+    hostname = socket.gethostname()
+except OSError:
+    host_info = None
+else:
+    domainname = '.'.join([x for x in fqdn.split('.')[1:]])
+    hostname = fqdn.split('.')[0]
+    environment = 'test' if 'test' in fqdn.split('.') else 'prod'
+    service = fqdn.split('.')[1]
+    host_info = {
+        "domainname": domainname,
+        "environment": environment,
+        "fqdn": fqdn,
+        "hostname": hostname
+    }
+
+def get_file_hash(modulesfile):
+    """
+    Based on https://github.com/python/cpython/pull/31930: should use
+    hashlib.file_digest() but it is only available in python 3.11
+    """
+    try:
+        with open(modulesfile, "rb") as fileobj:
+            digestobj = hashlib.sha256()
+            _bufsize = 2**18
+            buf = bytearray(_bufsize)  # Reusable buffer to reduce allocations.
+            view = memoryview(buf)
+            while True:
+                size = fileobj.readinto(buf)
+                if size == 0:
+                    break  # EOF
+                digestobj.update(view[:size])
+    except FileNotFoundError:
+        return ""
+
+    return digestobj.hexdigest()
+
+
+def get_list_hash(file_lines):
+    """Get hash of list contents"""
+
+    file_lines_hash = hashlib.sha256()
+    for line in file_lines:
+        file_lines_hash.update(line)
+
+    return file_lines_hash.hexdigest()
+
+
+def create_file_content(modules):
+    """
+    Write out the expected file contents to a list so we can check the
+    expected checksum before writing anything
+    """
+    file_lines = []
+    file_lines.append("# Generated by {}\n".format(  # pylint: disable=consider-using-f-string
+        os.path.basename(sys.argv[0])).encode("utf-8"))
+    for key in modules:
+        file_lines.append("{0:11} {1} {2} {3}\n".format(  # pylint: disable=consider-using-f-string
+            key,
+            modules[key]["repo"],
+            modules[key]["upgrade"],
+            modules[key]["tag"],
+        ).encode("utf-8"))
+
+    return file_lines
+
+
+def main():
+    """Starting point of the program"""
+
+    modulesfile: str = "/etc/puppet/cosmos-modules.conf"
+    modulesfile_tmp: str = modulesfile + ".tmp"
+
+    modules: dict = {
+        "apparmor": {
+            "repo": "https://github.com/SUNET/puppet-apparmor.git",
+            "upgrade": "yes",
+            "tag": "sunet-2*",
+        },
+        "bastion": {
+            "repo": "https://github.com/SUNET/puppet-bastion.git",
+            "upgrade": "yes",
+            "tag": "sunet-2*",
+        },
+        "nagioscfg": {
+            "repo": "https://github.com/SUNET/puppet-nagioscfg.git",
+            "upgrade": "yes",
+            "tag": "sunet-2*",
+        },
+        "sunet": {
+            "repo": "https://github.com/SUNET/puppet-sunet.git",
+            "upgrade": "yes",
+            "tag": "stable-2*",
+        },
+        "ufw": {
+            "repo": "https://github.com/SUNET/puppet-module-ufw.git",
+            "upgrade": "yes",
+           "tag": "sunet-2*",
+        },
+    }
+
+    # When/if we want we can do stuff to modules here
+    if host_info:
+        if host_info["environment"] == "test":
+            modules["sunet"]["tag"] = "testing-2*"
+    #   if host_info["fqdn"] == "k8sw1.matrix.test..sunet.se":
+    #       modules["sunet"]["tag"] = "mandersson-test*" 
+    # Build list of expected file content
+    file_lines = create_file_content(modules)
+
+    # Get hash of the list
+    list_hash = get_list_hash(file_lines)
+
+    # Get hash of the existing file on disk
+    file_hash = get_file_hash(modulesfile)
+
+    # Update the file if necessary
+    if list_hash != file_hash:
+        # Since we are reading the file with 'rb' when computing our hash use 'wb' when
+        # writing so we dont end up creating a file that does not match the
+        # expected hash
+        with open(modulesfile_tmp, "wb") as fileobj:
+            for line in file_lines:
+                fileobj.write(line)
+
+        # Rename it in place so the update is atomic for anything else trying to
+        # read the file
+        os.rename(modulesfile_tmp, modulesfile)
+
+
+if __name__ == "__main__":
+    main()