Preserve PostgreSQL node identities across role changes (#26)

Author: gauravtiwari

CHANGELOG.md

@@ -7,6 +7,13 @@ and this project follows [Semantic Versioning](https://semver.org/).
 
 ## Unreleased
 
+## 0.9.8 - 2026-10-02
+
+### Fixed
+
+- Support explicit node IDs so repmgr identities survive primary changes and standby reordering.
+- Reject duplicate or invalid node IDs before deployment.
+
 ## 0.9.7 - 2026-09-01
 
 ### Added

Gemfile.lock

@@ -1,7 +1,7 @@
 PATH
   remote: .
   specs:
-    active_postgres (0.9.7)
+    active_postgres (0.9.8)
       bcrypt_pbkdf (~> 1.1)
       ed25519 (~> 1.4)
       pg (~> 1.6)

README.md

@@ -76,6 +76,12 @@ manual-promotion while the ordinary standby retains automatic failover.
 settings before repmgr registration, avoiding a full base-backup stream from
 the primary. The `pgbackrest` component must be enabled.
 
+Set a unique positive integer `node_id` on every primary and standby entry
+before permanently changing their roles or reordering standbys. Match the
+existing IDs in `repmgr cluster show`, and keep each ID with its host after a
+switchover. Without explicit IDs, the primary defaults to 1 and standbys use
+their list position starting at 2. Duplicate or invalid IDs are rejected.
+
 Add credentials (`rails credentials:edit`):
 
 ```yaml

lib/active_postgres/components/repmgr.rb

@@ -28,7 +28,7 @@ def uninstall
       end
 
       def uninstall_from(host)
-        node_id = host == config.primary_host ? 1 : (config.standby_hosts.index(host) || 997) + 2
+        node_id = config.node_id_for(host)
 
         ssh_executor.execute_on_host(host) do
           cluster_output = begin
@@ -98,6 +98,7 @@ def setup_primary
         puts '  Setting up primary with repmgr...'
 
         host = config.primary_host
+        primary_node_id = config.node_id_for(host)
         repmgr_config = config.repmgr_config_for(host)
         version = config.version
         repmgr_password = normalize_repmgr_password(secrets.resolve('repmgr_password'))
@@ -208,7 +209,7 @@ def setup_primary
           unless cluster_show&.match?(/primary/i)
             # Fallback: verify via repmgr metadata in the repmgr database
             db_check = executor.run_sql_on_backend(self,
-                                                   'SELECT type FROM repmgr.nodes WHERE node_id = 1;',
+                                                   "SELECT type FROM repmgr.nodes WHERE node_id = #{primary_node_id};",
                                                    postgres_user: 'postgres',
                                                    database: repmgr_db,
                                                    tuples_only: true,
@@ -250,7 +251,7 @@ def setup_standby(standby_host)
         _ = repmgr_config
         _ = secrets_obj
 
-        node_id = config.standby_hosts.index(standby_host) + 2
+        node_id = config.node_id_for(standby_host)
         repmgr_password = normalize_repmgr_password(secrets_obj.resolve('repmgr_password'))
         replication_password = normalize_replication_password(secrets_obj.resolve('replication_password'))
         if replication_user == repmgr_user && replication_password != repmgr_password
@@ -679,6 +680,7 @@ def verify_cluster_health
         puts 'Verifying PostgreSQL HA cluster health...'
 
         primary_host = config.primary_host
+        primary_node_id = config.node_id_for(primary_host)
         standby_hosts = config.standby_hosts
         version = config.version
         postgres_user = config.postgres_user
@@ -709,12 +711,12 @@ def verify_cluster_health
           cluster_output = capture(:sudo, '-u', 'postgres',
                                    'repmgr', '-f', '/etc/repmgr.conf', 'cluster', 'show',
                                    raise_on_non_zero_exit: false).to_s
-          # Primary always has node_id=1, check if it's registered and running
-          if cluster_output.match?(/\s+1\s+\|.*primary.*\*\s+running/i)
+          # Check the configured node identity, which survives role changes.
+          if cluster_output.match?(/\s+#{primary_node_id}\s+\|.*primary.*\*\s+running/i)
             info '✓ Primary is registered with repmgr'
           else
             db_check = executor.run_sql_on_backend(self,
-                                                   'SELECT type FROM repmgr.nodes WHERE node_id = 1 AND active IS TRUE;',
+                                                   "SELECT type FROM repmgr.nodes WHERE node_id = #{primary_node_id} AND active IS TRUE;",
                                                    postgres_user: postgres_user,
                                                    database: repmgr_db,
                                                    tuples_only: true,
@@ -951,7 +953,7 @@ def reload_postgres_cluster
 
       def ensure_primary_registered
         host = config.primary_host
-        config.version
+        primary_node_id = config.node_id_for(host)
         is_registered = false
 
         ssh_executor.execute_on_host(host) do
@@ -965,8 +967,8 @@ def ensure_primary_registered
             ''
           end
 
-          if cluster_output.include?('| 1') && cluster_output.include?('primary')
-            info '✓ Primary is registered (node_id=1)'
+          if cluster_output.match?(/\b#{primary_node_id}\s+\|.*primary/)
+            info "✓ Primary is registered (node_id=#{primary_node_id})"
           else
             warn "⚠ Primary not found in cluster, assuming it's registered"
           end

lib/active_postgres/configuration.rb

@@ -1,11 +1,13 @@
 require 'yaml'
 require_relative 'configuration/pgbackrest_policy'
 require_relative 'configuration/standby_policy'
+require_relative 'configuration/node_identity'
 
 module ActivePostgres
   class Configuration
     include PgBackRestPolicy
     include StandbyPolicy
+    include NodeIdentity
 
     attr_reader :environment, :version, :user, :ssh_key, :ssh_known_hosts_file, :ssh_host_key_verification,
                 :primary, :standbys, :jump_hosts, :components, :secrets_config, :database_config
@@ -147,6 +149,8 @@ def node_label_for(host)
     def validate!
       raise Error, 'No primary host defined' unless primary_host
 
+      validate_node_ids!
+
       # Validate required secrets if components are enabled
       raise Error, 'Missing replication_password secret' if component_enabled?(:repmgr) && !secrets_config['replication_password']
       raise Error, 'Missing monitoring_password secret' if component_enabled?(:monitoring) && !secrets_config['monitoring_password']

lib/active_postgres/configuration/node_identity.rb

@@ -0,0 +1,22 @@
+module ActivePostgres
+  class Configuration
+    module NodeIdentity
+      def node_id_for(host)
+        node = node_config_for(host)
+        raise Error, "Unknown PostgreSQL host: #{host}" unless node
+
+        value = node.fetch('node_id') { host == primary_host ? 1 : standby_hosts.index(host) + 2 }
+        raise Error, "node_id for #{host} must be a positive 32-bit integer" unless value.is_a?(Integer) && value.between?(1, 2_147_483_647)
+
+        value
+      end
+
+      private
+
+      def validate_node_ids!
+        node_ids = all_hosts.map { |host| node_id_for(host) }
+        raise Error, 'PostgreSQL node_id values must be unique' unless node_ids.uniq.size == node_ids.size
+      end
+    end
+  end
+end

lib/active_postgres/version.rb

@@ -1,3 +1,3 @@
 module ActivePostgres
-  VERSION = '0.9.7'.freeze
+  VERSION = '0.9.8'.freeze
 end

templates/repmgr.conf.erb

@@ -9,7 +9,7 @@
     end
   end
 %>
-node_id=<%= host == config.primary_host ? 1 : config.standby_hosts.index(host) + 2 %>
+node_id=<%= config.node_id_for(host) %>
 node_name='<%= node_label %>'
 <%
   # conninfo describes how OTHER nodes connect to THIS node

test/components/repmgr_templates_test.rb

@@ -36,6 +36,14 @@ def test_conf_uses_private_ip_for_conninfo
     assert_includes content, "conninfo='host=10.0.0.10 user=repmgr dbname=repmgr connect_timeout=2'"
   end
 
+  def test_conf_preserves_explicit_node_ids_after_role_change
+    @config.primary['node_id'] = 3
+    @config.standbys.first['node_id'] = 1
+
+    assert_includes render_conf({}, host: 'primary.example.com'), 'node_id=3'
+    assert_includes render_conf({}, host: 'standby.example.com'), 'node_id=1'
+  end
+
   def test_conf_sets_automatic_failover_by_default
     content = render_conf({}, host: 'primary.example.com')
 

test/configuration_node_identity_test.rb

@@ -0,0 +1,43 @@
+require 'test_helper'
+
+class ConfigurationNodeIdentityTest < Minitest::Test
+  def test_legacy_configuration_keeps_position_based_ids
+    config = configuration({ 'host' => 'a' }, [{ 'host' => 'b' }])
+
+    assert config.validate!
+    assert_equal 1, config.node_id_for('a')
+    assert_equal 2, config.node_id_for('b')
+  end
+
+  def test_explicit_identities_survive_switchover_and_standby_reordering
+    nodes = %w[a b c].each_with_index.map { |host, index| { 'host' => host, 'node_id' => index + 1 } }
+    before = configuration(nodes[0], [nodes[1], nodes[2]])
+    after = configuration(nodes[2], [nodes[1], nodes[0]])
+
+    assert before.validate!
+    assert after.validate!
+    nodes.each do |node|
+      assert_equal before.node_id_for(node['host']), after.node_id_for(node['host'])
+    end
+  end
+
+  def test_rejects_explicit_and_implicit_id_collision
+    config = configuration({ 'host' => 'a', 'node_id' => 2 }, [{ 'host' => 'b' }])
+
+    error = assert_raises(ActivePostgres::Error) { config.validate! }
+    assert_match(/must be unique/, error.message)
+  end
+
+  def test_rejects_invalid_ids_before_rendering_sql_or_configuration
+    [0, -1, 2_147_483_648, '3', '1; DROP TABLE nodes', nil, 1.5].each do |value|
+      config = configuration({ 'host' => 'a', 'node_id' => value }, [])
+      assert_raises(ActivePostgres::Error) { config.validate! }
+    end
+  end
+
+  private
+
+  def configuration(primary, standbys)
+    ActivePostgres::Configuration.new({ 'production' => { 'primary' => primary, 'standby' => standbys } }, 'production')
+  end
+end