# Testing Zero Downtime Upgrade Process

Zero Downtime upgrade eliminates any disruption to nova API service during upgrade.

Nova API services are upgraded at the end. The basic idea of the zero downtime upgrade process is to have the connections drain from the old API before being upgraded. In this process, new connections go to the new API nodes while old connections slowly drain from the old nodes. This ensures that the user sees the max_supported API version as a monotonically increasing number. There might be some performance degradation during the process due to slow HTTP responses and delayed request handling, but there is no API downtime.

This page describes how to test the zero downtime upgrade process.

## Environment

- Multinode devstack environment with 2 nodes:

    - controller - All services (N release)

    - compute-api - Only n-cpu and n-api services (N release)

- Highly available load balancer (HAProxy) on top of the n-api services. This is required for zero downtime upgrade as it allows one n-api service to run while we upgrade the other. See instructions to setup HAProxy below.

## Instructions to setup HAProxy

Install HAProxy and Keepalived on both nodes.

    # apt-get install haproxy keepalived

Let the kernel know that we intend to bind additional IP addresses that won’t be defined in the interfaces file. To do this, edit `/etc/sysctl.conf` and add the following line:

    net.ipv4.ip_nonlocal_bind=1

Make this take effect without rebooting.

    # sysctl -p

Configure HAProxy to add backend servers and assign virtual IP to the frontend. On both nodes add the below HAProxy config:

    # cd /etc/haproxy
    # cat >> haproxy.cfg <<EOF

       global
          chroot /var/lib/haproxy
          user haproxy
          group haproxy
          daemon
          log 192.168.0.88 local0
          pidfile  /var/run/haproxy.pid
          stats socket /var/run/haproxy.sock mode 600 level admin
          stats timeout 2m
          maxconn 4000

       defaults
          log  global
          maxconn  8000
          mode  http
          option  redispatch
          retries  3
          stats  enable
          timeout  http-request 10s
          timeout  queue 1m
          timeout  connect 10s
          timeout  client 1m
          timeout  server 1m
          timeout  check 10s

       frontend nova-api-vip
          bind 192.168.0.95:8282             <<ha proxy virtual ip>>
          default_backend nova-api

       backend nova-api
          balance  roundrobin
          option  tcplog
          server  controller 192.168.0.88:8774  check
          server  apicomp  192.168.0.89:8774  check

      EOF

Note

Just change the IP for log in the global section on each node.

On both nodes add `keepalived.conf`:

    # cd /etc/keepalived
    # cat >> keepalived.conf <<EOF

       global_defs {
          router_id controller
       }
       vrrp_script haproxy {
          script "killall -0 haproxy"
          interval 2
          weight 2
       }
       vrrp_instance 50 {
          virtual_router_id 50
          advert_int 1
          priority 101
          state MASTER
          interface eth0
          virtual_ipaddress {
             192.168.0.95 dev eth0
          }
          track_script {
             haproxy
          }
       }

     EOF

Note

Change priority on node2 to 100 ( or vice-versa). Add HAProxy virtual IP.

Restart keepalived service.

    # service keepalived restart

Add `ENABLED=1` in `/etc/default/haproxy` and then restart HAProxy service.

    # service haproxy restart

When both the services have restarted, node with the highest priority for keepalived claims the virtual IP. You can check which node claimed the virtual IP using:

    # ip a

## Zero Downtime upgrade process

General rolling upgrade process: Minimal Downtime Upgrade Process.

### Before Upgrade

- Change nova-api endpoint in keystone to point to the HAProxy virtual IP.

- Run tempest tests

- Check if n-api services on both nodes are serving the requests.

### Before maintenance window

- Start the upgrade process with controller node.

- Follow the steps from the general rolling upgrade process to install new code and sync the db for schema changes.

### During maintenance window

- Set compute option in upgrade_levels to auto in `nova.conf`.

      [upgrade_levels]
      compute = auto

- Starting with n-cond restart all services except n-api and n-cpu.

- In small batches gracefully shutdown nova-cpu, then start n-cpu service with new version of the code.

- Run tempest tests.

- Drain connections on n-api while the tempest tests are running. HAProxy allows you to drain the connections by setting weight to zero:

      # echo "set weight nova-api/<<server>> 0" | sudo socat /var/run/haproxy.sock stdio

- OR disable service using:

      # echo "disable server nova-api/<<server>>" | sudo socat /var/run/haproxy.sock stdio

- This allows the current node to complete all the pending requests. When this is being upgraded, other api node serves the requests. This way we can achieve zero downtime.

- Restart n-api service and enable n-api using the command:

      # echo "enable server nova-api/<<server>>" | sudo socat /var/run/haproxy.sock stdio

- Drain connections from other old api node in the same way and upgrade.

- No tempest tests should fail since there is no API downtime.

### After maintenance window

- Follow the steps from general rolling upgrade process to clear any cached service version data and complete all online data migrations.

this page last updated: 2026-06-10 20:07:09

Except where otherwise noted, this document is licensed under Creative Commons Attribution 3.0 License. See all OpenStack Legal Documents.

found an error? report a bug