high-availability

Redis 的 哨兵（Sentinel） Redis 的 Sentinel 系统用于管理多个 Redis 服务器（instance）， 该系统执行以下三个任务： 监控 ：哨兵会不断检查你的主服务器和从服务器是否运作正常。 提醒 ：当被监控的某个Redis服务器出现问题时，哨兵可以通过API给程序员发送通知 自动故障转移 ：主服务器宕机，哨兵会开始一次自动故障转移操作，升级一个从服务器为主服务器，并让其他从服务器改为复制新的主服务器；当客户端试图连接失效的主服务器时，集群也会向客户端返回新的主服务器地址，使得集群可以新的主服务器代替失效服务器。 注： Redis的哨兵是一个分布式系统 ，你可以在架构中运行多个哨兵进程，这些进程使用 gossip 协议 来接受主服务器是否下线的信息，并使用 投票协议 来决定是否执行故障转移，以及选择哪个从服务器作为新的主服务器 虽然 Redis 哨兵有一个单独的可执行文件 redis-sentinel ， 但实际上它只是一个运行 在特殊模式下的 Redis 服务器 ， 你可以在启动一个普通 Redis 服务器时通过给定 –sentinel 选项来启动 Redis 哨兵。 启动 Sentinel 对于 redis-sentinel 程序， 你可以用以下命令来启动 哨兵系统： 对于 redis-server 程序， 你可以用以下命令来启动一个运行在

hadoop集群搭建： 配置hosts （4个节点一致） 192.168.83.11 hd1 192.168.83.22 hd2 192.168.83.33 hd3 192.168.83.44 hd4 配置主机名（重启生效） [hadoop@hd1 ~]$ more /etc/sysconfig/network NETWORKING=yes HOSTNAME=hd1 配置用户用户组 [hadoop@hd1 ~]$ id hadoop uid=1001(hadoop) gid=10010(hadoop) groups=10010(hadoop) 配置JDK [hadoop@hd1 ~]$ env|grep JAVA JAVA_HOME=/usr/java/jdk1.8.0_11 [hadoop@hd1 ~]$ java -version java version "1.8.0_11" Java(TM) SE Runtime Environment (build 1.8.0_11-b12) Java HotSpot(TM) 64-Bit Server VM (build 25.11-b03, mixed mode) 配置ssh免密登录 ssh-keygen -t rsa ssh-keygen -t dsa cat ~/.ssh/*.pub > ~/.ssh/authorizedkeys

节点及实例规划： High Availability With QJM 部署要点及注意事项请参考 https://my.oschina.net/u/3862440/blog/2208568 HA 部署小节。 编辑"hdfs-site.xml" dfs.nameservices --配置命名服务,一个集群一个服务名，服务名下面包含多个服务和几点，对外统一提供服务。 <property> <name>dfs.nameservices</name> <value>mycluster</value> </property> dfs.ha.namenodes.[nameservice ID] --配置所有的NN的service id，一个service服务下面有多个NN节点，为了做NN高可用，集群必须知道每个节点的ID,以便区分。我这里规划了2个NN,所以NN ID有两个。 <property> <name>dfs.ha.namenodes.mycluster</name> <value>nn1,nn2</value> </property> dfs.namenode.rpc-address.[nameservice ID].[name node ID] --配置所有的NN的rpc协议（用于NN与DN或者客户端之间的数据传输），我这里配置了2个NN 3个DN

While this question is tagged EventMachine, generic BSD-socket solutions in any language are much appreciated too. Some background: I have an application listening on a TCP socket. It is started and shut down with a regular System V style init script. My problem is that it needs some time to start up before it is ready to service the TCP socket. It's not too long, perhaps only 5 seconds, but that's 5 seconds too long when a restart needs to be performed during a workday. It's also crucial that existing connections remain open and are finished normally. Reasons for a restart of the application

If I understand the CAP Theorem correctly, availability means that the cluster continues to operate even if a node goes down. I've seen a lot of people ( http://blog.nahurst.com/tag/guide ) list RDBMS as CA, but I do not understand how RBDMS is available, as if a node goes down, the cluster must go down to maintain consistency. My only possible answer to this has been that most RDBMS are a single node, so there is no "non-failing" node. But, this seems to be a technicality, not true 'availability' and definitely not high availability. Thank you. First of all, let me clarify and state that the

With HDFS or HFTP URI scheme (e.g. hdfs://namenode/path/to/file ) I can access HDFS clusters without requiring their XML configuration files. It is very handy when running shell commands like hdfs dfs -get , hadoop distcp or reading files from Spark like sc.hadoopFile() , because I don't have to copy and manage xml files for all relevant HDFS clusters to all nodes that those codes might potentially run. One drawback of this approach is that I have to use the active NameNode's hostname, otherwise Hadoop will throw an exception complaining that the NN is standby. A usual workaround is to try one

Hello fellow technicians, Let's assume we have a (PHP) website with millions of visitors a month and we running a SolR index on the website with 4 million documents hosted. Solr is running on 4 separate servers where one server is the master and other 3 servers are replicated. There can be inserted thousands of documents into Solr every 5 minutes. And besides that, user can update their account which also should trigger a solr update. I am looking for a safe strategy to rebuild the index fast and safe without missing any document. And to have a safe delta/update strategy. I have thought about