diff --git a/lib/hosting/gcp_apis.rb b/lib/hosting/gcp_apis.rb
index e227ac6a4..ae177500d 100644
--- a/lib/hosting/gcp_apis.rb
+++ b/lib/hosting/gcp_apis.rb
@@ -149,9 +149,8 @@ def get_vm(vm_name, zone)
     JSON.parse(response.body)
   end
 
-  def create_static_ipv4(vm_name, region)
+  def create_static_ipv4(address_name, region)
     connection = Excon.new(@host[:connection_string], headers: @host[:headers])
-    address_name = "#{vm_name}-addr"
     body = {
       name: address_name,
       networkTier: "PREMIUM",
@@ -161,9 +160,8 @@ def create_static_ipv4(vm_name, region)
     Hosting::GcpApis.check_errors(response)
   end
 
-  def get_static_ipv4(vm_name, region)
+  def get_static_ipv4(address_name, region)
     connection = Excon.new(@host[:connection_string], headers: @host[:headers])
-    address_name = "#{vm_name}-addr"
     response = connection.get(path: "/compute/v1/projects/#{@project}/regions/#{region}/addresses/#{address_name}", expects: 200)
     JSON.parse(response.body)
   end
@@ -194,9 +192,8 @@ def assign_static_ipv4(vm_name, addr, zone)
     wait_for_operation(zone, data["id"])
   end
 
-  def release_ipv4(vm_name, region)
+  def release_ipv4(address_name, region)
     connection = Excon.new(@host[:connection_string], headers: @host[:headers])
-    address_name = "#{vm_name}-addr"
     connection.delete(path: "/compute/v1/projects/#{@project}/regions/#{region}/addresses/#{address_name}", expects: [200, 404])
   end
 
diff --git a/migrate/20240618_gcp_vm_address_name.rb b/migrate/20240618_gcp_vm_address_name.rb
new file mode 100644
index 000000000..7617144ba
--- /dev/null
+++ b/migrate/20240618_gcp_vm_address_name.rb
@@ -0,0 +1,10 @@
+# frozen_string_literal: true
+
+Sequel.migration do
+  change do
+    alter_table(:gcp_vm) do
+      add_column :address_name, :text, collate: '"C"'
+    end
+    run "UPDATE gcp_vm SET address_name=name || '-addr'"
+  end
+end
diff --git a/model/gcp_vm.rb b/model/gcp_vm.rb
index dc18c7553..df53a3e98 100644
--- a/model/gcp_vm.rb
+++ b/model/gcp_vm.rb
@@ -66,4 +66,30 @@ def is_stopped?
   def self.redacted_columns
     super + [:public_key]
   end
+
+  def swap_ip(vm)
+    # swap ips in gcp
+    gcp_client = Hosting::GcpApis.new
+    zone1 = "#{location}-a"
+    zone2 = "#{vm.location}-a"
+    gcp_client.delete_ephermal_ipv4(name, zone1)
+    gcp_client.delete_ephermal_ipv4(vm.name, zone2)
+    gcp_client.assign_static_ipv4(name, vm.sshable.host, zone1)
+    gcp_client.assign_static_ipv4(vm.name, sshable.host, zone2)
+
+    # update sshable hosts
+    current_host = sshable.host
+    new_host = vm.sshable.host
+    sshable.update(host: "temp_#{name}")
+    vm.sshable.update(host: current_host)
+    sshable.update(host: new_host)
+    current_address_name = address_name
+
+    # update address names
+    update(address_name: vm.address_name)
+    vm.update(address_name: current_address_name)
+
+    sshable.invalidate_cache_entry
+    vm.sshable.invalidate_cache_entry
+  end
 end
diff --git a/model/lantern/lantern_doctor.rb b/model/lantern/lantern_doctor.rb
index 278057542..c5e664859 100644
--- a/model/lantern/lantern_doctor.rb
+++ b/model/lantern/lantern_doctor.rb
@@ -25,7 +25,7 @@ def has_system_query?(queries, query)
 
   def should_run?
     return false unless resource
-    resource.representative_server.display_state == "running" && resource.representative_server.strand.label == "wait"
+    resource.display_state == "running" && resource.representative_server.strand.label == "wait"
   end
 
   def sync_system_queries
diff --git a/model/lantern/lantern_resource.rb b/model/lantern/lantern_resource.rb
index fda3d96b4..a9eae65d5 100644
--- a/model/lantern/lantern_resource.rb
+++ b/model/lantern/lantern_resource.rb
@@ -51,6 +51,7 @@ def label
   end
 
   def display_state
+    return "failover" if servers.find { _1.display_state == "failover" }
     super || representative_server&.display_state || "unavailable"
   end
 
diff --git a/model/lantern/lantern_server.rb b/model/lantern/lantern_server.rb
index 2e498d15d..259d5ccf5 100644
--- a/model/lantern/lantern_server.rb
+++ b/model/lantern/lantern_server.rb
@@ -66,6 +66,7 @@ def display_state
     return "updating" if vm.display_state == "updating" || strand.label.include?("update") || strand.label == "init_sql"
     return "unavailable" if strand.label == "wait_db_available"
     return "running" if strand.label == "wait"
+    return "failover" if ["take_over", "wait_swap_ip", "promote_server"].include?(strand.label)
     "creating"
   end
 
@@ -114,8 +115,8 @@ def configure_hash
       db_user: resource.db_user || "",
       db_user_password: resource.db_user_password || "",
       postgres_password: resource.superuser_password || "",
-      # master_host: lantern_server.master_host,
-      # master_port: lantern_server.master_port,
+      master_host: resource.representative_server.hostname,
+      master_port: 5432,
       prom_password: Config.prom_password,
       gcp_creds_gcr_b64: Config.gcp_creds_gcr_b64,
       gcp_creds_coredumps_b64: Config.gcp_creds_coredumps_b64,
@@ -131,6 +132,15 @@ def configure_hash
     })
   end
 
+  def lazy_change_replication_mode(replication_mode)
+    update(timeline_access: (replication_mode == "master") ? "push" : "fetch", representative_at: (replication_mode == "master") ? Time.new : nil)
+    vm.sshable.cmd("sudo lantern/bin/lazy_update_env", stdin: JSON.generate([
+      ["POSTGRESQL_REPLICATION_MODE", replication_mode],
+      ["INSTANCE_TYPE", (replication_mode == "master") ? "writer" : "reader"],
+      ["POSTGRESQL_RECOVER_FROM_BACKUP", ""]
+    ]))
+  end
+
   def update_walg_creds
     walg_config = timeline.generate_walg_config
     vm.sshable.cmd("sudo lantern/bin/update_env", stdin: JSON.generate([
diff --git a/prog/gcp_vm/nexus.rb b/prog/gcp_vm/nexus.rb
index 8e9017925..ceab25701 100644
--- a/prog/gcp_vm/nexus.rb
+++ b/prog/gcp_vm/nexus.rb
@@ -66,7 +66,7 @@ def host
 
   label def wait_ipv4
     gcp_client = Hosting::GcpApis.new
-    addr_info = gcp_client.get_static_ipv4(gcp_vm.name, gcp_vm.location)
+    addr_info = gcp_client.get_static_ipv4(gcp_vm.address_name, gcp_vm.location)
     if addr_info["status"] == "RESERVED"
       gcp_client.delete_ephermal_ipv4(gcp_vm.name, "#{gcp_vm.location}-a")
       gcp_client.assign_static_ipv4(gcp_vm.name, addr_info["address"], "#{gcp_vm.location}-a")
@@ -82,7 +82,9 @@ def host
     gcp_client = Hosting::GcpApis.new
     vm = gcp_client.get_vm(gcp_vm.name, "#{gcp_vm.location}-a")
     if vm["status"] == "RUNNING"
-      gcp_client.create_static_ipv4(gcp_vm.name, gcp_vm.location)
+      address_name = "#{gcp_vm.name}-addr"
+      gcp_client.create_static_ipv4(address_name, gcp_vm.location)
+      gcp_vm.update(address_name: address_name)
       register_deadline(:wait, 5 * 60)
       hop_wait_ipv4
     else
@@ -229,7 +231,7 @@ def host
       gcp_client = Hosting::GcpApis.new
       gcp_client.delete_vm(gcp_vm.name, "#{gcp_vm.location}-a")
       if gcp_vm.has_static_ipv4
-        gcp_client.release_ipv4(gcp_vm.name, gcp_vm.location)
+        gcp_client.release_ipv4(gcp_vm.address_name, gcp_vm.location)
       end
       strand.children.each { _1.destroy }
       gcp_vm.projects.map { gcp_vm.dissociate_with_project(_1) }
diff --git a/prog/lantern/lantern_resource_nexus.rb b/prog/lantern/lantern_resource_nexus.rb
index b1d1afec1..c4df8b082 100644
--- a/prog/lantern/lantern_resource_nexus.rb
+++ b/prog/lantern/lantern_resource_nexus.rb
@@ -102,7 +102,16 @@ def self.assemble(project_id:, location:, name:, target_vm_size:, target_storage
       )
 
       lantern_resource.required_standby_count.times do
-        Prog::Lantern::LanternServerNexus.assemble(resource_id: lantern_resource.id, timeline_id: timeline_id, timeline_access: "fetch")
+        Prog::Lantern::LanternServerNexus.assemble(
+          resource_id: lantern_resource.id,
+          timeline_id: timeline_id,
+          timeline_access: "fetch",
+          lantern_version: lantern_version,
+          extras_version: extras_version,
+          minor_version: minor_version,
+          target_vm_size: target_vm_size,
+          target_storage_size_gib: target_storage_size_gib
+        )
       end
 
       Strand.create(prog: "Lantern::LanternResourceNexus", label: "start") { _1.id = lantern_resource.id }
@@ -152,7 +161,16 @@ def before_run
   label def wait
     # Create missing standbys
     (lantern_resource.required_standby_count + 1 - lantern_resource.servers.count).times do
-      Prog::Lantern::LanternServerNexus.assemble(resource_id: lantern_resource.id, timeline_id: lantern_resource.timeline.id, timeline_access: "fetch")
+      Prog::Lantern::LanternServerNexus.assemble(
+        resource_id: lantern_resource.id,
+        lantern_version: lantern_resource.representative_server.lantern_version,
+        extras_version: lantern_resource.representative_server.extras_version,
+        minor_version: lantern_resource.representative_server.minor_version,
+        target_vm_size: lantern_resource.representative_server.target_vm_size,
+        target_storage_size_gib: lantern_resource.representative_server.target_storage_size_gib,
+        timeline_id: lantern_resource.timeline.id,
+        timeline_access: "fetch"
+      )
     end
 
     if lantern_resource.display_state == "failed"
diff --git a/prog/lantern/lantern_server_nexus.rb b/prog/lantern/lantern_server_nexus.rb
index a22f2a637..05282ebb8 100644
--- a/prog/lantern/lantern_server_nexus.rb
+++ b/prog/lantern/lantern_server_nexus.rb
@@ -164,7 +164,7 @@ def before_run
   end
 
   label def wait_catch_up
-    query = "SELECT pg_current_wal_lsn() - replay_lsn FROM pg_stat_replication WHERE application_name = '#{lantern_server.ubid}'"
+    query = "SELECT pg_current_wal_lsn() - replay_lsn FROM pg_stat_replication WHERE application_name = 'walreceiver'"
     lag = lantern_server.resource.representative_server.run_query(query).chomp
 
     nap 30 if lag.empty? || lag.to_i > 80 * 1024 * 1024 # 80 MB or ~5 WAL files
@@ -175,7 +175,7 @@ def before_run
   end
 
   label def wait_synchronization
-    query = "SELECT sync_state FROM pg_stat_replication WHERE application_name = '#{lantern_server.ubid}'"
+    query = "SELECT sync_state FROM pg_stat_replication WHERE application_name = 'walreceiver'"
     sync_state = lantern_server.resource.representative_server.run_query(query).chomp
     hop_wait if ["quorum", "sync"].include?(sync_state)
 
@@ -442,9 +442,52 @@ def destroy_domain
       hop_update_vm_size
     end
 
+    when_take_over_set? do
+      hop_take_over
+    end
+
     nap 30
   end
 
+  label def promote_server
+    current_master = lantern_server.resource.representative_server
+    current_master_domain = current_master.domain
+    new_master_domain = lantern_server.domain
+
+    lantern_server.update(domain: current_master_domain)
+    current_master.update(domain: new_master_domain)
+
+    lantern_server.run_query("SELECT pg_promote(true, 120);")
+    current_master.lazy_change_replication_mode("slave")
+    lantern_server.lazy_change_replication_mode("master")
+
+    hop_wait
+  end
+
+  label def wait_swap_ip
+    # wait until ip change will propogate
+    begin
+      is_in_recovery = lantern_server.run_query("SELECT pg_is_in_recovery()").chomp == "t"
+      nap 5 if !is_in_recovery
+    rescue
+      nap 5
+    end
+
+    hop_promote_server
+  end
+
+  label def take_over
+    decr_take_over
+    if !lantern_server.standby?
+      hop_wait
+    end
+
+    lantern_server.vm.swap_ip(lantern_server.resource.representative_server.vm)
+
+    register_deadline(:promote_server, 5 * 60)
+    hop_wait_swap_ip
+  end
+
   label def unavailable
     # TODO
     # if postgres_server.primary? && (standby = postgres_server.failover_target)
diff --git a/rhizome/lantern/bin/lazy_update_env b/rhizome/lantern/bin/lazy_update_env
new file mode 100755
index 000000000..ab23f3992
--- /dev/null
+++ b/rhizome/lantern/bin/lazy_update_env
@@ -0,0 +1,11 @@
+#!/bin/env ruby
+# frozen_string_literal: true
+
+require "json"
+require "yaml"
+require_relative "../../common/lib/util"
+require_relative "../lib/common"
+
+env_arr = JSON.parse($stdin.read)
+
+append_env(env_arr)
diff --git a/spec/lib/hosting/gcp_apis_spec.rb b/spec/lib/hosting/gcp_apis_spec.rb
index b4b65f795..dd54f8cec 100644
--- a/spec/lib/hosting/gcp_apis_spec.rb
+++ b/spec/lib/hosting/gcp_apis_spec.rb
@@ -96,7 +96,7 @@
         stub_request(:post, "https://compute.googleapis.com/compute/v1/projects/test-project/regions/us-central1/addresses").to_return(status: 200, body: JSON.dump({}), headers: {"Content-Type" => "application/json"})
         stub_request(:get, "https://compute.googleapis.com/compute/v1/projects/test-project/regions/us-central1/addresses/dummy-vm-addr").to_return(status: 200, body: JSON.dump({status: "CREATING", address: "1.1.1.1"}), headers: {"Content-Type" => "application/json"})
         api = described_class.new
-        expect(api.get_static_ipv4("dummy-vm", "us-central1")).to eq({"status" => "CREATING", "address" => "1.1.1.1"})
+        expect(api.get_static_ipv4("dummy-vm-addr", "us-central1")).to eq({"status" => "CREATING", "address" => "1.1.1.1"})
       end
     end
 
@@ -155,7 +155,7 @@
         api = described_class.new
         stub_request(:post, "https://oauth2.googleapis.com/token").to_return(status: 200, body: JSON.dump({}), headers: {"Content-Type" => "application/json"})
         stub_request(:delete, "https://compute.googleapis.com/compute/v1/projects/test-project/regions/us-central1/addresses/dummy-vm-addr")
-        expect { api.release_ipv4("dummy-vm", "us-central1") }.not_to raise_error
+        expect { api.release_ipv4("dummy-vm-addr", "us-central1") }.not_to raise_error
       end
     end
 
diff --git a/spec/model/gcp_vm_spec.rb b/spec/model/gcp_vm_spec.rb
index 610dd3e6e..3acfd0584 100644
--- a/spec/model/gcp_vm_spec.rb
+++ b/spec/model/gcp_vm_spec.rb
@@ -6,7 +6,8 @@
   subject(:gcp_vm) {
     described_class.new(
       name: "vm1",
-      location: "us-central1"
+      location: "us-central1",
+      address_name: "vm1-addr"
     ) { _1.id = "c068cac7-ed45-82db-bf38-a003582b36ee" }
   }
 
@@ -70,4 +71,25 @@
       expect(gcp_vm.is_stopped?).to be(true)
     end
   end
+
+  describe "#swap_ip" do
+    it "swap server ips" do
+      api = instance_double(Hosting::GcpApis)
+      expect(api).to receive(:delete_ephermal_ipv4).with("vm1", "us-central1-a")
+      expect(api).to receive(:delete_ephermal_ipv4).with("vm2", "us-central1-a")
+      expect(api).to receive(:assign_static_ipv4).with("vm1", "ip2", "us-central1-a")
+      expect(api).to receive(:assign_static_ipv4).with("vm2", "ip1", "us-central1-a")
+      expect(Hosting::GcpApis).to receive(:new).and_return(api)
+      vm2 = instance_double(described_class, name: "vm2", address_name: "vm2-addr", location: "us-central1", sshable: instance_double(Sshable, host: "ip2"))
+      expect(gcp_vm).to receive(:sshable).and_return(instance_double(Sshable, host: "ip1")).at_least(:once)
+      expect(gcp_vm.sshable).to receive(:invalidate_cache_entry)
+      expect(vm2.sshable).to receive(:invalidate_cache_entry)
+      expect(gcp_vm.sshable).to receive(:update).with(host: "temp_vm1")
+      expect(gcp_vm.sshable).to receive(:update).with(host: "ip2")
+      expect(vm2.sshable).to receive(:update).with(host: "ip1")
+      expect(gcp_vm).to receive(:update).with(address_name: "vm2-addr")
+      expect(vm2).to receive(:update).with(address_name: "vm1-addr")
+      expect { gcp_vm.swap_ip(vm2) }.not_to raise_error
+    end
+  end
 end
diff --git a/spec/model/lantern/lantern_doctor_spec.rb b/spec/model/lantern/lantern_doctor_spec.rb
index 6979438a5..0ce7f0586 100644
--- a/spec/model/lantern/lantern_doctor_spec.rb
+++ b/spec/model/lantern/lantern_doctor_spec.rb
@@ -53,17 +53,17 @@
 
   describe "#should_run" do
     it "returns true" do
-      expect(lantern_doctor).to receive(:resource).and_return(instance_double(LanternResource, representative_server: instance_double(LanternServer, display_state: "running", strand: instance_double(Strand, label: "wait")))).at_least(:once)
+      expect(lantern_doctor).to receive(:resource).and_return(instance_double(LanternResource, display_state: "running", representative_server: instance_double(LanternServer, strand: instance_double(Strand, label: "wait")))).at_least(:once)
       expect(lantern_doctor.should_run?).to be(true)
     end
 
     it "returns false if not running" do
-      expect(lantern_doctor).to receive(:resource).and_return(instance_double(LanternResource, representative_server: instance_double(LanternServer, display_state: "stopped", strand: instance_double(Strand, label: "start")))).at_least(:once)
+      expect(lantern_doctor).to receive(:resource).and_return(instance_double(LanternResource, display_state: "failover", representative_server: instance_double(LanternServer, strand: instance_double(Strand, label: "start")))).at_least(:once)
       expect(lantern_doctor.should_run?).to be(false)
     end
 
     it "returns false" do
-      expect(lantern_doctor).to receive(:resource).and_return(instance_double(LanternResource, representative_server: instance_double(LanternServer, display_state: "running", strand: instance_double(Strand, label: "start")))).at_least(:once)
+      expect(lantern_doctor).to receive(:resource).and_return(instance_double(LanternResource, display_state: "running", representative_server: instance_double(LanternServer, display_state: "running", strand: instance_double(Strand, label: "start")))).at_least(:once)
       expect(lantern_doctor.should_run?).to be(false)
     end
 
diff --git a/spec/model/lantern/lantern_resource_spec.rb b/spec/model/lantern/lantern_resource_spec.rb
index 32ac4e682..496ec839f 100644
--- a/spec/model/lantern/lantern_resource_spec.rb
+++ b/spec/model/lantern/lantern_resource_spec.rb
@@ -29,6 +29,16 @@
     expect(lantern_resource.display_state).to eq("running")
   end
 
+  it "returns failed as display state" do
+    expect(lantern_resource).to receive(:display_state).and_return("failed")
+    expect(lantern_resource.display_state).to eq("failed")
+  end
+
+  it "returns failover" do
+    expect(lantern_resource).to receive(:servers).and_return([instance_double(LanternServer, display_state: "running", strand: instance_double(Strand, label: "wait")), instance_double(LanternServer, display_state: "failover", strand: instance_double(Strand, label: "take_over"))])
+    expect(lantern_resource.display_state).to eq("failover")
+  end
+
   it "returns unavailable as display state if no representative_server" do
     expect(lantern_resource).to receive(:representative_server).and_return(nil)
     expect(lantern_resource.display_state).to eq("unavailable")
diff --git a/spec/model/lantern/lantern_server_spec.rb b/spec/model/lantern/lantern_server_spec.rb
index 4d74390ff..8bed14d8d 100644
--- a/spec/model/lantern/lantern_server_spec.rb
+++ b/spec/model/lantern/lantern_server_spec.rb
@@ -15,7 +15,7 @@
   let(:vm) {
     instance_double(
       GcpVm,
-      sshable: instance_double(Sshable),
+      sshable: instance_double(Sshable, host: "127.0.0.1"),
       mem_gib: 8
     )
   }
@@ -115,6 +115,24 @@
       expect(lantern_server).to receive(:strand).and_return(instance_double(Strand, label: "unknown")).at_least(:once)
       expect(lantern_server.display_state).to eq("failed")
     end
+
+    it "shows failover when label is take_over" do
+      expect(lantern_server.vm).to receive(:display_state).and_return("running").at_least(:once)
+      expect(lantern_server).to receive(:strand).and_return(instance_double(Strand, label: "take_over")).at_least(:once)
+      expect(lantern_server.display_state).to eq("failover")
+    end
+
+    it "shows failover when label is wait_swap_ip" do
+      expect(lantern_server.vm).to receive(:display_state).and_return("running").at_least(:once)
+      expect(lantern_server).to receive(:strand).and_return(instance_double(Strand, label: "wait_swap_ip")).at_least(:once)
+      expect(lantern_server.display_state).to eq("failover")
+    end
+
+    it "shows failover when label is promote_server" do
+      expect(lantern_server.vm).to receive(:display_state).and_return("running").at_least(:once)
+      expect(lantern_server).to receive(:strand).and_return(instance_double(Strand, label: "promote_server")).at_least(:once)
+      expect(lantern_server.display_state).to eq("failover")
+    end
   end
 
   it "returns name from ubid" do
@@ -248,6 +266,7 @@
         superuser_password: "pwd1234",
         gcp_creds_b64: "test-creds",
         recovery_target_lsn: nil,
+        representative_server: lantern_server,
         restore_target: nil)
       expect(Config).to receive(:prom_password).and_return("pwd123").at_least(:once)
       expect(Config).to receive(:gcp_creds_gcr_b64).and_return("test-creds").at_least(:once)
@@ -278,6 +297,8 @@
         db_user: resource.db_user || "",
         db_user_password: resource.db_user_password || "",
         postgres_password: resource.superuser_password || "",
+        master_host: resource.representative_server.hostname,
+        master_port: 5432,
         prom_password: Config.prom_password,
         gcp_creds_gcr_b64: Config.gcp_creds_gcr_b64,
         gcp_creds_coredumps_b64: Config.gcp_creds_coredumps_b64,
@@ -313,6 +334,7 @@
         superuser_password: "pwd1234",
         gcp_creds_b64: "test-creds",
         recovery_target_lsn: nil,
+        representative_server: lantern_server,
         restore_target: Time.now)
       expect(Config).to receive(:prom_password).and_return("pwd123").at_least(:once)
       expect(Config).to receive(:gcp_creds_gcr_b64).and_return("test-creds").at_least(:once)
@@ -344,6 +366,8 @@
         db_user: resource.db_user || "",
         db_user_password: resource.db_user_password || "",
         postgres_password: resource.superuser_password || "",
+        master_host: resource.representative_server.hostname,
+        master_port: 5432,
         prom_password: Config.prom_password,
         gcp_creds_gcr_b64: Config.gcp_creds_gcr_b64,
         gcp_creds_coredumps_b64: Config.gcp_creds_coredumps_b64,
@@ -378,6 +402,7 @@
         superuser_password: "pwd1234",
         gcp_creds_b64: "test-creds",
         recovery_target_lsn: "16/B374D848",
+        representative_server: lantern_server,
         restore_target: nil)
       expect(Config).to receive(:prom_password).and_return("pwd123").at_least(:once)
       expect(Config).to receive(:gcp_creds_gcr_b64).and_return("test-creds").at_least(:once)
@@ -408,6 +433,8 @@
         db_user: resource.db_user || "",
         db_user_password: resource.db_user_password || "",
         postgres_password: resource.superuser_password || "",
+        master_host: resource.representative_server.hostname,
+        master_port: 5432,
         prom_password: Config.prom_password,
         gcp_creds_gcr_b64: Config.gcp_creds_gcr_b64,
         gcp_creds_coredumps_b64: Config.gcp_creds_coredumps_b64,
@@ -442,6 +469,7 @@
         superuser_password: "pwd1234",
         gcp_creds_b64: "test-creds",
         recovery_target_lsn: "16/B374D848",
+        representative_server: lantern_server,
         restore_target: Time.now)
       expect(Config).to receive(:prom_password).and_return("pwd123").at_least(:once)
       expect(Config).to receive(:gcp_creds_gcr_b64).and_return("test-creds").at_least(:once)
@@ -473,6 +501,8 @@
         db_user: resource.db_user || "",
         db_user_password: resource.db_user_password || "",
         postgres_password: resource.superuser_password || "",
+        master_host: resource.representative_server.hostname,
+        master_port: 5432,
         prom_password: Config.prom_password,
         gcp_creds_gcr_b64: Config.gcp_creds_gcr_b64,
         gcp_creds_coredumps_b64: Config.gcp_creds_coredumps_b64,
@@ -519,7 +549,7 @@
 
   describe "Lsn monitor" do
     it "fails to initiate a new health monitor session" do
-      expect(lantern_server).to receive(:strand).and_return(instance_double(Strand, label: "setup domain")).at_least(:once)
+      expect(lantern_server).to receive(:strand).and_return(instance_double(Strand, label: "setup domain")).at_least(:once).at_least(:once)
       expect { lantern_server.init_health_monitor_session }.to raise_error "server is not ready to initialize session"
     end
 
@@ -539,8 +569,8 @@
       }
 
       expect(lantern_server).to receive(:destroy_set?).and_return(false)
-      expect(lantern_server).to receive(:display_state).and_return("running")
-      expect(lantern_server).to receive(:strand).and_return(instance_double(Strand, label: "wait"))
+      expect(lantern_server).to receive(:display_state).and_return("running").at_least(:once)
+      expect(lantern_server).to receive(:strand).and_return(instance_double(Strand, label: "wait")).at_least(:once)
       expect(lantern_server).not_to receive(:incr_checkup)
       lantern_server.check_pulse(session: session, previous_pulse: pulse)
     end
@@ -555,9 +585,9 @@
         reading_chg: Time.now - 30
       }
 
-      expect(lantern_server).to receive(:display_state).and_return("running")
+      expect(lantern_server).to receive(:display_state).and_return("running").at_least(:once)
       expect(lantern_server).to receive(:destroy_set?).and_return(false)
-      expect(lantern_server).to receive(:strand).and_return(instance_double(Strand, label: "wait"))
+      expect(lantern_server).to receive(:strand).and_return(instance_double(Strand, label: "wait")).at_least(:once)
       expect(lantern_server).to receive(:primary?).and_return(true)
       expect(lantern_server).not_to receive(:incr_checkup)
       lantern_server.check_pulse(session: session, previous_pulse: pulse)
@@ -573,9 +603,9 @@
         reading_chg: Time.now - 30
       }
 
-      expect(lantern_server).to receive(:display_state).and_return("running")
+      expect(lantern_server).to receive(:display_state).and_return("running").at_least(:once)
       expect(lantern_server).to receive(:destroy_set?).and_return(false)
-      expect(lantern_server).to receive(:strand).and_return(instance_double(Strand, label: "wait"))
+      expect(lantern_server).to receive(:strand).and_return(instance_double(Strand, label: "wait")).at_least(:once)
       expect(session[:db_connection]).to receive(:[]).and_raise(Sequel::DatabaseConnectionError)
       expect(lantern_server).to receive(:incr_checkup)
       lantern_server.check_pulse(session: session, previous_pulse: pulse)
@@ -677,4 +707,28 @@
       expect(described_class.get_vm_image("0.2.7", "0.1.5", "1")).to eq("custom-image")
     end
   end
+
+  describe "#lazy_change_replication_mode" do
+    it "changes to master" do
+      time = Time.new
+      expect(lantern_server.vm.sshable).to receive(:cmd).with("sudo lantern/bin/lazy_update_env", stdin: JSON.generate([
+        ["POSTGRESQL_REPLICATION_MODE", "master"],
+        ["INSTANCE_TYPE", "writer"],
+        ["POSTGRESQL_RECOVER_FROM_BACKUP", ""]
+      ]))
+      expect(Time).to receive(:new).and_return(time)
+      expect(lantern_server).to receive(:update).with(timeline_access: "push", representative_at: time)
+      lantern_server.lazy_change_replication_mode("master")
+    end
+
+    it "changes to slave" do
+      expect(lantern_server.vm.sshable).to receive(:cmd).with("sudo lantern/bin/lazy_update_env", stdin: JSON.generate([
+        ["POSTGRESQL_REPLICATION_MODE", "slave"],
+        ["INSTANCE_TYPE", "reader"],
+        ["POSTGRESQL_RECOVER_FROM_BACKUP", ""]
+      ]))
+      expect(lantern_server).to receive(:update).with(timeline_access: "fetch", representative_at: nil)
+      lantern_server.lazy_change_replication_mode("slave")
+    end
+  end
 end
diff --git a/spec/prog/gcp_vm/nexus_spec.rb b/spec/prog/gcp_vm/nexus_spec.rb
index aeae878d5..a401cb039 100644
--- a/spec/prog/gcp_vm/nexus_spec.rb
+++ b/spec/prog/gcp_vm/nexus_spec.rb
@@ -92,15 +92,17 @@
       gcp_api = instance_double(Hosting::GcpApis)
       expect(Hosting::GcpApis).to receive(:new).and_return(gcp_api)
       expect(gcp_api).to receive(:get_vm).with("dummy-vm", "us-central1-a").and_return({"status" => "RUNNING"})
-      expect(gcp_api).to receive(:create_static_ipv4).with("dummy-vm", "us-central1").and_return({})
+      expect(gcp_api).to receive(:create_static_ipv4).with("dummy-vm-addr", "us-central1").and_return({})
       expect(gcp_vm).to receive(:strand).and_return(instance_double(Strand, prog: "GcpVm", stack: [{}])).at_least(:once)
+      expect(gcp_vm).to receive(:update).with(address_name: "dummy-vm-addr")
       expect { nx.wait_create_vm }.to hop("wait_ipv4")
     end
 
     it "naps if ip4 is not yet reserved" do
       gcp_api = instance_double(Hosting::GcpApis)
       expect(Hosting::GcpApis).to receive(:new).and_return(gcp_api)
-      expect(gcp_api).to receive(:get_static_ipv4).with("dummy-vm", "us-central1").and_return({"status" => "CREATING", "address" => "1.1.1.1"})
+      expect(gcp_vm).to receive(:address_name).and_return("dummy-vm-addr")
+      expect(gcp_api).to receive(:get_static_ipv4).with("dummy-vm-addr", "us-central1").and_return({"status" => "CREATING", "address" => "1.1.1.1"})
       expect { nx.wait_ipv4 }.to nap(10)
     end
 
@@ -109,7 +111,8 @@
       expect(gcp_vm).to receive(:sshable).and_return(sshable)
       gcp_api = instance_double(Hosting::GcpApis)
       expect(Hosting::GcpApis).to receive(:new).and_return(gcp_api)
-      expect(gcp_api).to receive(:get_static_ipv4).with("dummy-vm", "us-central1").and_return({"status" => "RESERVED", "address" => "1.1.1.1"})
+      expect(gcp_vm).to receive(:address_name).and_return("dummy-vm-addr")
+      expect(gcp_api).to receive(:get_static_ipv4).with("dummy-vm-addr", "us-central1").and_return({"status" => "RESERVED", "address" => "1.1.1.1"})
       expect(gcp_api).to receive(:delete_ephermal_ipv4).with("dummy-vm", "us-central1-a")
       expect(gcp_api).to receive(:assign_static_ipv4).with("dummy-vm", "1.1.1.1", "us-central1-a")
       expect(gcp_vm).to receive(:update).with({has_static_ipv4: true})
@@ -174,7 +177,8 @@
       gcp_api = instance_double(Hosting::GcpApis)
       expect(Hosting::GcpApis).to receive(:new).and_return(gcp_api)
       expect(gcp_api).to receive(:delete_vm).with("dummy-vm", "us-central1-a")
-      expect(gcp_api).to receive(:release_ipv4).with("dummy-vm", "us-central1")
+      expect(gcp_vm).to receive(:address_name).and_return("dummy-vm-addr")
+      expect(gcp_api).to receive(:release_ipv4).with("dummy-vm-addr", "us-central1")
       expect { nx.destroy }.to exit({"msg" => "gcp vm deleted"})
     end
   end
diff --git a/spec/prog/lantern/lantern_resource_nexus_spec.rb b/spec/prog/lantern/lantern_resource_nexus_spec.rb
index d122c40e6..e1779f966 100644
--- a/spec/prog/lantern/lantern_resource_nexus_spec.rb
+++ b/spec/prog/lantern/lantern_resource_nexus_spec.rb
@@ -21,6 +21,12 @@
       )],
       representative_server: instance_double(
         LanternServer,
+        lantern_version: Config.lantern_default_version,
+        extras_version: Config.lantern_extras_default_version,
+        minor_version: Config.lantern_minor_default_version,
+        target_vm_size: "n1-standard-2",
+        target_storage_size_gib: 64,
+
         vm: instance_double(
           GcpVm,
           id: "104b0033-b3f6-8214-ae27-0cd3cef18ce5"
diff --git a/spec/prog/lantern/lantern_server_nexus_spec.rb b/spec/prog/lantern/lantern_server_nexus_spec.rb
index 9595237df..5c090d36a 100644
--- a/spec/prog/lantern/lantern_server_nexus_spec.rb
+++ b/spec/prog/lantern/lantern_server_nexus_spec.rb
@@ -703,6 +703,11 @@
       expect { nx.wait }.to hop("unavailable")
     end
 
+    it "hops to take_over" do
+      nx.incr_take_over
+      expect { nx.wait }.to hop("take_over")
+    end
+
     it "decrements checkup" do
       nx.incr_checkup
       expect(nx).to receive(:available?).and_return(true)
@@ -914,4 +919,51 @@
       expect { nx.wait_timeline_available }.to hop("wait_db_available")
     end
   end
+
+  describe "#take_over" do
+    it "returns if primary" do
+      expect(lantern_server).to receive(:standby?).and_return(false)
+      expect(lantern_server).not_to receive(:run_query)
+      expect { nx.take_over }.to hop("wait")
+    end
+
+    it "swap ips" do
+      expect(lantern_server).to receive(:standby?).and_return(true)
+
+      current_master = instance_double(LanternServer, domain: "db1.lantern.dev", vm: instance_double(GcpVm, sshable: instance_double(Sshable, host: "127.0.0.1"), name: "old-master", location: "us-east1", address_name: "old-addr"))
+      expect(lantern_server.resource).to receive(:representative_server).and_return(current_master).at_least(:once)
+
+      expect(lantern_server.vm).to receive(:swap_ip).with(current_master.vm)
+
+      expect { nx.take_over }.to hop("wait_swap_ip")
+    end
+
+    it "waits until vm available" do
+      expect(lantern_server).to receive(:run_query).with("SELECT pg_is_in_recovery()").and_raise "test"
+      expect { nx.wait_swap_ip }.to nap 5
+    end
+
+    it "waits until ip swap done" do
+      expect(lantern_server).to receive(:run_query).with("SELECT pg_is_in_recovery()").and_return("f")
+      expect { nx.wait_swap_ip }.to nap 5
+    end
+
+    it "hops to promote" do
+      expect(lantern_server).to receive(:run_query).with("SELECT pg_is_in_recovery()").and_return("t")
+      expect { nx.wait_swap_ip }.to hop("promote_server")
+    end
+
+    it "promotes server" do
+      current_master = instance_double(LanternServer, domain: "db1.lantern.dev", vm: instance_double(GcpVm, sshable: instance_double(Sshable, host: "127.0.0.1"), name: "old-master", location: "us-east1", address_name: "old-addr"))
+      expect(lantern_server.resource).to receive(:representative_server).and_return(current_master).at_least(:once)
+
+      expect(current_master).to receive(:update).with(domain: lantern_server.domain).at_least(:once)
+      expect(lantern_server).to receive(:update).with(domain: current_master.domain).at_least(:once)
+
+      expect(lantern_server).to receive(:run_query).with("SELECT pg_promote(true, 120);")
+      expect(current_master).to receive(:lazy_change_replication_mode).with("slave")
+      expect(lantern_server).to receive(:lazy_change_replication_mode).with("master")
+      expect { nx.promote_server }.to hop("wait")
+    end
+  end
 end
diff --git a/spec/serializers/api/lantern_spec.rb b/spec/serializers/api/lantern_spec.rb
index cb7d605ea..c6a52860e 100644
--- a/spec/serializers/api/lantern_spec.rb
+++ b/spec/serializers/api/lantern_spec.rb
@@ -75,7 +75,8 @@
       display_state: "running",
       instance_type: "writer",
       hostname: "db.lantern.dev",
-      connection_string: "postgres://postgres:test123@db.lantern.dev:6432")
+      connection_string: "postgres://postgres:test123@db.lantern.dev:6432",
+      strand: instance_double(Strand, label: "wait"))
     expect(lantern).to receive(:representative_server).and_return(leader).at_least(:once)
     expect(lantern).to receive(:servers).and_return([leader]).at_least(:once)
     data = described_class.new(:detailed).serialize(lantern)
diff --git a/spec/serializers/web/lantern_spec.rb b/spec/serializers/web/lantern_spec.rb
index 07df261ae..2ad3f4d7a 100644
--- a/spec/serializers/web/lantern_spec.rb
+++ b/spec/serializers/web/lantern_spec.rb
@@ -77,6 +77,7 @@
       instance_type: "writer",
       hostname: "db.lantern.dev",
       primary?: true,
+      strand: instance_double(Strand, label: "wait"),
       connection_string: "postgres://postgres:test123@db.lantern.dev:6432")
     expect(lantern).to receive(:representative_server).and_return(leader).at_least(:once)
     expect(lantern).to receive(:servers).and_return([leader]).at_least(:once)