基于Redis的CAS集群

单点登录（SSO）是复杂应用系统的基本需求，Yale CAS是目前常用的开源解决方案。CAS认证中心，基于其特殊作用，自然会成为整个应用系统的核心，所有应用系统的认证工作，都将请求到CAS来完成。因此CAS服务器是整个应用的关键节点，CAS发生故障，所有系统都将陷入瘫痪。同时，CAS的负载能力要足够强，能够承担所有的认证请求响应。利用负载均衡和集群技术，不仅能克服CAS单点故障，同时将认证请求分布到多台CAS服务器上，有效减轻单台CAS服务器的请求压力。下面将基于CAS 3.4.5来讨论下CAS集群。

CAS的工作原理，主要是基于票据(Ticket)来实现的（参见 CAS基本原理）。CAS票据，存储在TicketRegistry中，因此要想实现CAS Cluster, 必须要多台CAS之间共享所有的Ticket，采用统一的TicketRegistry，可以达到此目的。  缺省的CAS实现中，TicketRegistry在内存中实现，不同的CAS服务器有自己单独的TicketRegistry，因此是不支持分布式集群的。但CAS提供了支持TicketRegistry分布式的接口 org.jasig.cas.ticket.registry.AbstractDistributedTicketRegistry，我们可以实现这个接口实现多台CAS服务器TicketRegistry共享，从而实现CAS集群。

同时，较新版本CAS使用SpringWebFlow作为认证流程，而webflow需要使用session存储流程相关信息，因此实现CAS集群，我们还得需要让不同服务器的session进行共享。

我们采用内存数据库Redis来实现TicketRegistry,让多个CAS服务器共用同一个TicketRegistry。同样方法，我们让session也存储在Redis中，达到共享session的目的。下面就说说如何用 Redis来实现TicketRegistry，我们使用Java调用接口Jedis来操作Redis，代码如下：

    import java.io.ByteArrayInputStream;        import java.io.ByteArrayOutputStream;        import java.io.ObjectInputStream;        import java.io.ObjectOutputStream;        import java.util.Collection;                import org.jasig.cas.ticket.Ticket;        import org.jasig.cas.ticket.TicketGrantingTicket;        import org.jasig.cas.ticket.registry.AbstractDistributedTicketRegistry;                        import redis.clients.jedis.Jedis;        import redis.clients.jedis.JedisPool;        import redis.clients.jedis.JedisPoolConfig;                        /*         *  TicketRegistry using Redis, to solve CAS Cluster.         *           *  @author ZL         *          */                public class RedisTicketRegistry extends AbstractDistributedTicketRegistry {                                private static int redisDatabaseNum;            private static String hosts;            private static int port;                 private static int st_time;  //ST最大空闲时间                  private static int tgt_time; //TGT最大空闲时间                        private static JedisPool cachePool;                        static {                            redisDatabaseNum = PropertiesConfigUtil.getPropertyInt("redis_database_num");                hosts = PropertiesConfigUtil.getProperty("hosts");                port = PropertiesConfigUtil.getPropertyInt("port");                st_time = PropertiesConfigUtil.getPropertyInt("st_time");                tgt_time = PropertiesConfigUtil.getPropertyInt("tgt_time");                cachePool = new JedisPool(new JedisPoolConfig(), hosts, port);                            }                        public void addTicket(Ticket ticket) {                                    Jedis jedis = cachePool.getResource();                jedis.select(redisDatabaseNum);                                          int seconds = 0;                                  String key = ticket.getId() ;                                if(ticket instanceof TicketGrantingTicket){                    //key = ((TicketGrantingTicket)ticket).getAuthentication().getPrincipal().getId();                    seconds = tgt_time/1000;                }else{                    seconds = st_time/1000;                }                                          ByteArrayOutputStream bos = new ByteArrayOutputStream();                ObjectOutputStream oos = null;                try{                    oos = new ObjectOutputStream(bos);                    oos.writeObject(ticket);                                   }catch(Exception e){                    log.error("adding ticket to redis error.");                }finally{                    try{                         if(null!=oos) oos.close();                    }catch(Exception e){                        log.error("oos closing error when adding ticket to redis.");                    }                }                jedis.set(key.getBytes(), bos.toByteArray());                jedis.expire(key.getBytes(), seconds);                                cachePool.returnResource(jedis);                            }                        public Ticket getTicket(final String ticketId) {                return getProxiedTicketInstance(getRawTicket(ticketId));            }                                    private Ticket getRawTicket(final String ticketId) {                                if(null == ticketId) return null;                                Jedis jedis = cachePool.getResource();                jedis.select(redisDatabaseNum);                                Ticket ticket = null;                                ByteArrayInputStream bais = new ByteArrayInputStream(jedis.get(ticketId.getBytes()));                ObjectInputStream ois = null;                                try{                    ois = new ObjectInputStream(bais);                    ticket = (Ticket)ois.readObject();                 }catch(Exception e){                    log.error("getting ticket to redis error.");                }finally{                    try{                        if(null!=ois)  ois.close();                    }catch(Exception e){                        log.error("ois closing error when getting ticket to redis.");                    }                }                                cachePool.returnResource(jedis);                                return ticket;            }                                           public boolean deleteTicket(final String ticketId) {                                if (ticketId == null) {                    return false;                }                                                Jedis jedis = cachePool.getResource();                jedis.select(redisDatabaseNum);                                    jedis.del(ticketId.getBytes());                                cachePool.returnResource(jedis);                                return true;                    }                     public Collection<Ticket> getTickets() {                                throw new UnsupportedOperationException("GetTickets not supported.");                    }                    protected boolean needsCallback() {                return false;            }                        protected void updateTicket(final Ticket ticket) {                addTicket(ticket);            }                 }  

    <!-- Ticket Registry -->    <bean id="ticketRegistry" class="org.jasig.cas.util.RedisTicketRegistry" />     <!--  <bean id="ticketRegistry" class="org.jasig.cas.ticket.registry.DefaultTicketRegistry" />   --> 

因为使用了Redis的expire功能，注释掉如下代码：

    <!-- TICKET REGISTRY CLEANER -->        lt;!--  <bean id="ticketRegistryCleaner" class="org.jasig.cas.ticket.registry.support.DefaultTicketRegistryCleaner"            p:ticketRegistry-ref="ticketRegistry" />                <bean id="jobDetailTicketRegistryCleaner" class="org.springframework.scheduling.quartz.MethodInvokingJobDetailFactoryBean"            p:targetObject-ref="ticketRegistryCleaner"            p:targetMethod="clean" />                <bean id="triggerJobDetailTicketRegistryCleaner" class="org.springframework.scheduling.quartz.SimpleTriggerBean"            p:jobDetail-ref="jobDetailTicketRegistryCleaner"            p:startDelay="20000"            p:repeatInterval="5000000" /> -->