puppet: Generate sharding in puppet, then refresh-sharding-and-restart.

This supports running puppet to pick up new sharding changes, which
will warn of the need to finalize them via
`refresh-sharding-and-restart`, or simply running that directly.

puppet/zulip/manifests/tornado_sharding.pp

@@ -7,13 +7,17 @@ class zulip::tornado_sharding {
   # with the correct default content for the "only one shard" setup. For this
   # reason they use "replace => false", because the files are managed by
   # the sharding script afterwards and puppet shouldn't overwrite them.
+
+  # The sha256 of the empty hash, used to fingerprint the configs as
+  # having been generated with a null sharding configuration.
+  $empty_sha256 = sha256('')
   file { '/etc/zulip/nginx_sharding.conf':
     ensure  => file,
     owner   => 'root',
     group   => 'root',
     mode    => '0644',
     notify  => Service['nginx'],
-    content => "set \$tornado_server http://tornado;\n",
+    content => "# Configuration hash: ${empty_sha256}\nset \$tornado_server http://tornado;\n",
     replace => false,
   }
   file { '/etc/zulip/sharding.json':
@@ -26,6 +30,14 @@ class zulip::tornado_sharding {
     replace => false,
   }
 
+  exec { 'write_updated_sharding':
+    command   => "${::zulip_scripts_path}/lib/sharding.py",
+    unless    => "${::zulip_scripts_path}/lib/sharding.py --verify",
+    require   => [File['/etc/zulip/nginx_sharding.conf']],
+    logoutput => true,
+    loglevel  => 'warning',
+  }
+
   # The number of Tornado processes to run on the server; this
   # defaults to 1, since Tornado sharding is currently only at the
   # Realm level.

scripts/lib/sharding.py

@@ -1,4 +1,6 @@
 #!/usr/bin/env python3
+import argparse
+import hashlib
 import json
 import os
 import subprocess
@@ -19,6 +21,15 @@ def write_realm_nginx_config_line(f: Any, host: str, port: str) -> None:
     set $tornado_server http://tornado{port};
 }}\n""")
 
+def hash_sharding_config() -> str:
+    config_file = get_config_file()
+    if not config_file.has_section("tornado_sharding"):
+        return hashlib.sha256(b'').hexdigest()
+    contents = subprocess.check_output([
+        "crudini", "--get", "--format=lines", "/etc/zulip/zulip.conf", "tornado_sharding",
+    ])
+    return hashlib.sha256(contents).hexdigest()
+
 # Basic system to do Tornado sharding.  Writes two output .tmp files that need
 # to be renamed to the following files to finalize the changes:
 # * /etc/zulip/nginx_sharding.conf; nginx needs to be reloaded after changing.
@@ -26,8 +37,28 @@ def write_realm_nginx_config_line(f: Any, host: str, port: str) -> None:
 # after changing.  TODO: We can probably make this live-reload by statting the file.
 #
 # TODO: Restructure this to automatically generate a sharding layout.
+
+parser = argparse.ArgumentParser(description="Adjust Tornado sharding configuration")
+parser.add_argument("--verify", action='store_true',
+                    help="Exits 0 with no action if no changes are required; exits 1 if changes would be made.")
+options = parser.parse_args()
+
+new_hash = hash_sharding_config()
+if os.path.exists('/etc/zulip/nginx_sharding.conf') and os.path.exists('/etc/zulip/sharding.json'):
+    with open('/etc/zulip/nginx_sharding.conf') as old_file:
+        if new_hash in old_file.read():
+            sys.exit(0)
+
+if options.verify:
+    sys.exit(1)
+
+if "SUPPRESS_SHARDING_NOTICE" not in os.environ:
+    print("** Updated sharding; scripts/refresh-sharding-and-restart required")
+
 with open('/etc/zulip/nginx_sharding.conf.tmp', 'w') as nginx_sharding_conf_f, \
         open('/etc/zulip/sharding.json.tmp', 'w') as sharding_json_f:
+    # Puppet uses this to know if it needs to rewrite the files
+    nginx_sharding_conf_f.write(f"# Configuration hash: {new_hash}\n")
 
     config_file = get_config_file()
     if not config_file.has_section("tornado_sharding"):

scripts/refresh-sharding-and-restart

@@ -2,8 +2,16 @@
 
 set -e
 
-"$(dirname "$0")/zulip-puppet-apply" -f
-# The step above should have generated the config files, now we need to move them into place:
+# Stand up the new zulip-tornado supervisor instances, and write out
+# the newly generated config files, with .tmp suffix
+SUPPRESS_SHARDING_NOTICE=1 "$(dirname "$0")/zulip-puppet-apply" -f
+
+# Verify, before we move them into place
+if ! [ -e /etc/zulip/nginx_sharding.conf.tmp ] || ! [ -e /etc/zulip/sharding.json.tmp ]; then
+    echo "No sharding updates found to apply."
+    exit 1
+fi
+
 chown root:root /etc/zulip/nginx_sharding.conf.tmp
 chmod 644 /etc/zulip/nginx_sharding.conf.tmp
 chown zulip:zulip /etc/zulip/sharding.json.tmp