Kolla Ansible supports a Highly Available (HA) deployment of
Openstack and other services. High-availability in Kolla
is implented as via Keepalived and HAProxy. Keepalived manages virtual IP
addresses, while HAProxy load-balances traffic to service backends.
These two components must be installed on the same hosts
and they are deployed to hosts in the
Preparation and deployment¶
HAProxy and Keepalived are enabled by default. They may be disabled by
setting the following in
enable_haproxy: "no" enable_keepalived: "no"
When a VIP fails over from one host to another, hosts may take some time to detect that the connection has been dropped. This can lead to service downtime.
To reduce the time by the kernel to close dead connections to VIP
address, modify the
net.ipv4.tcp_retries2 kernel option by setting
the following in
This is especially helpful for connections to MariaDB. See here, here and here for further information about this kernel option.
When different baremetal are used in infrastructure as haproxy backends or they are overloaded for some reason, kolla-ansible is able to change weight of backend per sevice. Weight can be any integer value from 1 to 256.
To set weight of backend per service, modify inventory file as below:
[control] server1 haproxy_nova_api_weight=10 server2 haproxy_nova_api_weight=2 haproxy_keystone_internal_weight=10 server3 haproxy_keystone_admin_weight=50