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Merge "Document testing process for zero downtime upgrade"

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doc/source/index.rst
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gmr gmr
testing/libvirt-numa testing/libvirt-numa
testing/serial-console testing/serial-console
testing/zero-downtime-upgrade
Sample Configuration File Sample Configuration File
------------------------- -------------------------

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=====================================
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.
.. code-block:: bash
# 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:
.. code-block:: INI
net.ipv4.ip_nonlocal_bind=1
Make this take effect without rebooting.
.. code-block:: bash
# sysctl -p
Configure HAProxy to add backend servers and assign virtual IP to the frontend.
On both nodes add the below HAProxy config:
.. code-block:: bash
# 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``:
.. code-block:: bash
# 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.
.. code-block:: bash
# service keepalived restart
Add ``ENABLED=1`` in ``/etc/default/haproxy`` and then restart HAProxy service.
.. code-block:: bash
# 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:
.. code-block:: bash
# ip a
------------------------------
Zero Downtime upgrade process
------------------------------
General rolling upgrade process:
http://docs.openstack.org/developer/nova/upgrade.html#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``.
.. code-block:: bash
[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:
.. code-block:: bash
# echo "set weight nova-api/<<server>> 0" | sudo socat /var/run/haproxy.sock stdio
* OR disable service using:
.. code-block:: bash
# 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:
.. code-block:: bash
# 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.