upgrade-zulip: Pin the postgres version to the OS default.

We would prefer to use the postgres packages from Postgres themselves,
if available.  However, this requires ensures that, for existing
installs, we preserve the same version of postgres as their base
distribution installed.

Move the version-determination logic from being computed at puppet
interpolation time, to being computed at install time and pinned into
zulip.conf.

puppet/zulip/manifests/base.pp

@@ -56,20 +56,7 @@ class zulip::base {
   }
   package { $base_packages: ensure => 'installed' }
 
-  $postgres_version = zulipconf('postgresql', 'version', $release_name ? {
-    'wheezy'  => '9.1',
-    'jessie'  => '9.4',
-    'stretch' => '9.6',
-    'buster'  => '11',
-    'precise' => '9.1',
-    'trusty'  => '9.3',
-    'vivid'   => '9.4',
-    'wily'    => '9.4',
-    'xenial'  => '9.5',
-    'bionic'  => '10',
-    'CentOS7' => '10',
-    'focal'   => '12',
-  })
+  $postgres_version = zulipconf('postgresql', 'version', undef)
 
   $normal_queues = [
     'deferred_work',

scripts/lib/upgrade-zulip-stage-2

@@ -12,6 +12,10 @@ import os
 import subprocess
 import sys
 import time
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    from typing import NoReturn
 
 os.environ["PYTHONUNBUFFERED"] = "y"
 
@@ -27,6 +31,7 @@ from scripts.lib.zulip_tools import (
     get_config,
     get_config_file,
     parse_os_release,
+    set_config,
     su_to_zulip,
 )
 
@@ -36,6 +41,17 @@ logging.Formatter.converter = time.gmtime
 logging.basicConfig(format="%(asctime)s upgrade-zulip-stage-2: %(message)s",
                     level=logging.INFO)
 
+
+def error_desupported_os(vendor: str, os_version: str) -> "NoReturn":
+    # Link to documentation for how to correctly upgrade the OS.
+    logging.critical("Unsupported platform: %s %s", vendor, os_version)
+    logging.info("Sorry! The support for your OS has been discontinued.\n"
+                 "Please upgrade your OS to a supported release first.\n"
+                 "See https://zulip.readthedocs.io/en/latest/production/"
+                 "upgrade-or-modify.html#upgrading-the-operating-system")
+    sys.exit(1)
+
+
 # Do not upgrade on unsupported OS versions.
 UNSUPPORTED_DISTROS = [
     ('ubuntu', '14.04'),
@@ -47,13 +63,7 @@ vendor = distro_info['ID']
 os_version = distro_info['VERSION_ID']
 
 if (vendor, os_version) in UNSUPPORTED_DISTROS:
-    # Link to documentation for how to correctly upgrade the OS.
-    logging.critical("Unsupported platform: %s %s", vendor, os_version)
-    logging.info("Sorry! The support for your OS has been discontinued.\n"
-                 "Please upgrade your OS to a supported release first.\n"
-                 "See https://zulip.readthedocs.io/en/latest/production/"
-                 "upgrade-or-modify.html#upgrading-the-operating-system")
-    sys.exit(1)
+    error_desupported_os(vendor, os_version)
 
 # make sure we have appropriate file permissions
 os.umask(0o22)
@@ -96,6 +106,23 @@ def shutdown_server() -> None:
                           preexec_fn=su_to_zulip)
     IS_SERVER_UP = False
 
+# postgresql.version is required for database servers, but wasn't
+# previously; fill it in based on what the OS provides.
+if os.path.exists('/etc/init.d/postgresql'):
+    postgres_version = get_config(config_file, 'postgresql', 'version')
+    if not postgres_version:
+        default_postgres_version = {
+            ('debian', '10'): '11',
+            ('ubuntu', '18.04'): '10',
+            ('ubuntu', '20.04'): '12',
+            ('centos', '7'): '11',
+        }
+        if (vendor, os_version) in default_postgres_version:
+            postgres_version = default_postgres_version[(vendor, os_version)]
+        else:
+            error_desupported_os(vendor, os_version)
+        set_config(config_file, 'postgresql', 'version', postgres_version)
+
 if glob.glob("/usr/share/postgresql/*/extension/tsearch_extras.control"):
     # Remove legacy tsearch_extras package references
     subprocess.check_call([

scripts/lib/zulip_tools.py

@@ -489,6 +489,16 @@ def get_config(
         return config_file.get(section, key)
     return default_value
 
+def set_config(
+    config_file: configparser.RawConfigParser,
+    section: str,
+    key: str,
+    value: str,
+) -> None:
+    if not config_file.has_section(section):
+        config_file.add_section(section)
+    config_file.set(section, key, value)
+
 def get_config_file() -> configparser.RawConfigParser:
     config_file = configparser.RawConfigParser()
     config_file.read("/etc/zulip/zulip.conf")