diff --git a/ansible/roles/neutron/defaults/main.yml b/ansible/roles/neutron/defaults/main.yml
index 09f6f91bf7..a7d71395b8 100644
--- a/ansible/roles/neutron/defaults/main.yml
+++ b/ansible/roles/neutron/defaults/main.yml
@@ -594,6 +594,10 @@ neutron_tls_proxy_extra_volumes: "{{ neutron_extra_volumes }}"
 dhcp_agents_per_network: 2
 max_l3_agents_per_router: 3
 
+# Adds a delay (in seconds) to the serial neutron_l3_agent container restart
+# process, allowing routers to fail over without loss of connectivity.
+neutron_l3_agent_failover_delay: 0
+
 ovsdb_timeout: 10
 
 neutron_logging_debug: "{{ openstack_logging_debug }}"
diff --git a/ansible/roles/neutron/handlers/main.yml b/ansible/roles/neutron/handlers/main.yml
index 20981506a2..5a3609eb16 100644
--- a/ansible/roles/neutron/handlers/main.yml
+++ b/ansible/roles/neutron/handlers/main.yml
@@ -87,7 +87,23 @@
   when:
     - kolla_action != "config"
 
-- name: Restart neutron-l3-agent container
+- name: Get container facts
+  become: true
+  kolla_container_facts:
+    container_engine: "{{ kolla_container_engine }}"
+    name:
+      - neutron_l3_agent
+  register: container_facts
+  when:
+    - kolla_action != "config"
+  listen: Restart neutron-l3-agent container
+
+- name: Group hosts
+  group_by:
+    key: neutron_l3_agent_running_{{ container_facts['neutron_l3_agent'] is defined }}
+  listen: Restart neutron-l3-agent container
+
+- name: Start stopped neutron-l3-agent container
   vars:
     service_name: "neutron-l3-agent"
     service: "{{ neutron_services[service_name] }}"
@@ -104,6 +120,41 @@
     healthcheck: "{{ service.healthcheck | default(omit) }}"
   when:
     - kolla_action != "config"
+    - groups['neutron_l3_agent_running_False'] is defined
+    - inventory_hostname in groups['neutron_l3_agent_running_False']
+  listen: Restart neutron-l3-agent container
+
+- name: Wait if container starting
+  wait_for:
+    timeout: "{{ neutron_l3_agent_failover_delay }}"
+  when:
+    - groups['neutron_l3_agent_running_False'] is defined
+    - groups['neutron_l3_agent_running_True'] is defined
+    - kolla_action != "config"
+  listen: Restart neutron-l3-agent container
+
+- name: Restart running neutron-l3-agent container
+  vars:
+    service_name: "neutron-l3-agent"
+    service: "{{ neutron_services[service_name] }}"
+  become: true
+  kolla_docker:
+    action: "recreate_or_restart_container"
+    common_options: "{{ docker_common_options }}"
+    name: "{{ service.container_name }}"
+    image: "{{ service.image }}"
+    environment: "{{ service.environment }}"
+    volumes: "{{ service.volumes | reject('equalto', '') | list }}"
+    dimensions: "{{ service.dimensions }}"
+    privileged: "{{ service.privileged | default(False) }}"
+    healthcheck: "{{ service.healthcheck | default(omit) }}"
+  when:
+    - kolla_action != "config"
+    - inventory_hostname == item
+  loop: "{{ groups['neutron_l3_agent_running_True'] | default([]) }}"
+  loop_control:
+    pause: "{{ neutron_l3_agent_failover_delay }}"
+  listen: Restart neutron-l3-agent container
 
 - name: Restart neutron-sriov-agent container
   vars:
diff --git a/doc/source/reference/networking/neutron.rst b/doc/source/reference/networking/neutron.rst
index eedbf786b6..cac383bf92 100644
--- a/doc/source/reference/networking/neutron.rst
+++ b/doc/source/reference/networking/neutron.rst
@@ -109,6 +109,36 @@ to using the native OVS firewall driver by employing a configuration override
    [securitygroup]
    firewall_driver = openvswitch
 
+L3 agent high availability
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+L3 and DHCP agents can be created in a high availability (HA) state with:
+
+.. code-block:: yaml
+
+   enable_neutron_agent_ha: "yes"
+
+This allows networking to fail over across controllers if the active agent is
+stopped. If this option is enabled, it can be advantageous to also set:
+
+.. code-block:: yaml
+
+   neutron_l3_agent_failover_delay:
+
+Agents sometimes need to be restarted. This delay (in seconds) is invoked
+between the restart operations of each agent. When set properly, it will stop
+network outages caused by all agents restarting at the same time. The exact
+length of time it takes to restart is dependent on hardware and the number of
+routers present. A general rule of thumb is to set the value to ``40 + 3n``
+where ``n`` is the number of routers. For example, with 5 routers,
+``40 + (3 * 5) = 65`` so the value could be set to 65. A much better approach
+however would be to first time how long an outage lasts, then set the value
+accordingly.
+
+The default value is 0. A nonzero starting value would only result in
+outages if the failover time was greater than the delay, which would be more
+difficult to diagnose than consistent behaviour.
+
 OVN (ml2/ovn)
 ~~~~~~~~~~~~~
 
diff --git a/releasenotes/notes/serial-l3-agent-restart-with-delay-7c2ec5875dbb760e.yaml b/releasenotes/notes/serial-l3-agent-restart-with-delay-7c2ec5875dbb760e.yaml
new file mode 100644
index 0000000000..e5f796337f
--- /dev/null
+++ b/releasenotes/notes/serial-l3-agent-restart-with-delay-7c2ec5875dbb760e.yaml
@@ -0,0 +1,11 @@
+---
+fixes:
+  - |
+    In HA mode, parallel restart of neutron-l3-agent containers will cause
+    a network outage. Adding routers increases the recovery time. This
+    release makes restarts serial and adds a user-configurable delay to ensure
+    each agent is returned to operation before the next one is restarted.
+
+    The default value is 0. A nonzero starting value would only result in
+    outages if the failover time was greater than the delay, which would be
+    more difficult to diagnose than consistent behaviour.