根据服务自身状况，HA 分为 Active/Active 和 Active/Passive 两种

    Active/Active:   适合于 stateless/stateful 服务，常用 load balance + keepalive(VIP) 配置 HA
    Active/Passive: 适用于 stateful 服务，常用 load balance + keepalive(VIP) + pacemaker + Corosync 配置 HA

Openstack HA 实现

   Database(Active/Active):
       官方推荐：MySQL with Galera
       http://docs.openstack.org/high-availability-guide/content/ha-aa-db.html

   AMQP(Active/Active): 
       官方推荐：RabbitMQ cluster
       https://openstack.redhat.com/RabbitMQ

   Openstack API(Active/Active):
       keystone, glance-api, glance-registry, neutron-server, ceilometer-api, dashboard。
       均为 stateless 服务，通过 Load balance + keepalive 保证 HA，部署于 Apache server 可提高性能，Haproxy(1.5.0)支持 SSL。
       Loadbalance for openstack api
       http://openstack.redhat.com/Load_Balance_OpenStack_API
       Configuration SSL for haproxy
       http://www.b2btech.in/implement-ssl-termination-haproxy-ubuntu-14-04
       Runs openstack api in apache
       http://andy.mc.it/2013/07/apache2-mod_wsgi-openstack-pt-2-nova-api-os-compute-nova-api-ec2/#comment-35

   Openstack scheduler(Active/Active):
       nova-scheduler, nova-conductor, nova-consoleauth, nova-novncproxy, ceilometer-collector, cinder-scheduler。
       均为 stateless 服务，恰当的配置与 AMQP server 连接参数即可
       http://docs.openstack.org/high-availability-guide/content/_run_openstack_api_and_schedulers.html

   Memcached(Active/Active):
       1. 提高 Dashboard 的性能
       2. 解决 nova-consoleauth 单点问题
       https://code.google.com/p/memcached/wiki/NewStart

   Network:
       1.  neutron DHCP agent(Active/Passive)
       2.  neutron L3 agent(Active/Passive)
       3.  neutron metadata agent(Active/Passive) 
       以上三者均由 Pacemaker + Corosync 配置
       http://docs.openstack.org/high-availability-guide/content/ch-network.html
 

   Storage:
      ceph 保证 image storage, volume storage, nova backend 可靠性
      http://www.ceph.com/docs/next/rbd/rbd-openstack/

Openstack 高可靠部署方案