Introduction to the Redis cluster
Download & install Redis
Set up the Redis cluster
- Manual setup
- Automatic mode connection

Introduction to the Redis cluster

Redis Cluster is a distributed storage solution officially released by Redis 3.0. Fully decentralized, consisting of multiple nodes, all connected to each other. The Redis client can connect to any node directly to obtain a key pair in the cluster without the need for an intermediary agent. If the node does not have a key specified by the user, the client is automatically redirected to the node where the key is located.

A Redis cluster is a network structure where each node is connected to each other via TCP connections. In a cluster of N nodes, each node has n-1 outgoing TCP connections, and n-1 incoming connections, and these TCP connections remain permanent.

Like other distributed storage systems, Redis Cluster provides the following functions:

Data partition Redis cluster will disperse user data to each node, exceeding the maximum storage capacity of single Redis memory. The cluster introduces the concept of hash slots. After the establishment of hash slots, 16,384 hash slots will be generated, and 16,384 hash slots will be mapped to different nodes roughly equally based on the number of nodes. When a user stores a key-value, the cluster performs CRC16 verification on the key and then takes the module of 16384 to determine which slot to place the key-value in. In this way, data is automatically divided to different nodes.

Data redundancy Redis clusters support master/slave replication and failover. The cluster uses a master-slave replication model. Each master node must have at least one slave node. If a primary node fails, all its children broadcast a packet to the other primary nodes in the cluster to request votes. Once a secondary node receives a majority of responses from the primary nodes, it wins the election and is elected as the primary node to handle the hash slot that the old primary node used to handle.

For detailed introduction and implementation principle of Redis Cluster, please refer to Redis Cluster tutorial and Redis Cluster specification.Copy the code

Download & install Redis

Experimental Environment Information Linux version: CentOS Linux release 7.4.1708 Redis version: 5.0.3Copy the code

Install a stand-alone Redis on the server or VM. If the Redis has been installed, you can skip this section.

Access the Redis installation directory.

Copycd /usr/local
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Download and unzip the Redis source code package.

Copywget http://download.redis.io/releases/redis-5.0.3.tar.gz tar - ZXVF redis - 5.0.3. Tar. GzCopy the code

Then go to the decompressed directory and use the make command to compile and install Redis.

Copycd redis-5.0.3
make && make install
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Don’t be happy, because it is highly likely that you will run into compile failures because the GCC compiler is not installed. Take your time and execute the following commands in sequence.

Copyyum -y install gcc
make distclean
make && make install
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Redis is based on C, so compiling source code requires GCC (a compiler under Linux, which is used to compile '. C 'files) support. If it is not installed on the machine, run 'yum -y install GCC' to install the GCC compiler, 'make distclean' to remove the previously generated files, and 'make && make install' to compile and install again.Copy the code

If output similar to the following is displayed, Redis is successfully installed.

Copy...... Hint: It's a good idea to run 'make test' ;) INSTALL install INSTALL install INSTALL install INSTALL install INSTALL install make[1]: Leaving the /usr/local/redis-5.0.3/src directoryCopy the code

If the source code is correctly compiled and executed, the make install command will install the program to the specified directory, usually /usr/local/bin. You can verify the installation using the following command output: Of course, you can also use the make install PREFIX= command to install to the specified path.

Copy[root@localhost bin]# CD /usr/local/bin [root@localhost bin]# ls -l total amount 32672-rwxr-xr-x. 1 root root 4367328 March 6 06:11 redis-benchmark-rwxr-xr-x. 1 root root 8092024 3月 6 06:11 redis-check-aof -rwxr-xr-x. 1 root root 8092024 3月 6 06:11 redis-check-rdb-rwxr-xr-x. 1 root root 4802696 March 6 06:11 redis-cli LRWXRWXRWX. 1 root root 12 March 6 06:11 Redis-sentinel-redis-server-rwxr-xr-x. 1 root root 8092024 3月 6 06:11 redis-serverCopy the code

At this point, the standalone Redis installation is complete.

Set up the Redis cluster

Let’s get down to business.

According to the internal failover implementation principle of Redis Cluster, a Redis Cluster needs at least three master nodes, and each master node has at least one slave node. Therefore, a Cluster should contain at least six nodes, three master nodes and three slave nodes, and be deployed on different machines.

The conditions are limited. In the test environment, we can only create a pseudo cluster on one machine and start multiple Instances of Redis through different TCP ports to form a cluster.

At present, there are two ways to build Redis Cluster:

Manually set up a cluster by running the cluster command.
In automatic mode, the cluster management tool is used to quickly set up the cluster.

The principle of the two methods is the same. The automatic construction method only encapsulates the Redis command to be executed in the manual construction method into an executable program. In the production environment, you are advised to use the second method, which is simple and easy to error. However, both methods will be mentioned in this practical demonstration.

Manual setup

Start node

The first step in building a cluster is to start up each node that participates in the cluster.

Since we are simulating multiple nodes on one machine, we can plan the attributes of each node in advance:

Node number	The IP address	TCP port	The node type	From the node	A launch configuration
A	127.0.0.1	7001	The main	D	/usr/local/redis-cluster/7001/redis.conf
B	127.0.0.1	7002	The main	E	/usr/local/redis-cluster/7002/redis.conf
C	127.0.0.1	7003	The main	F	/usr/local/redis-cluster/7003/redis.conf
D	127.0.0.1	8001	from	/	/usr/local/redis-cluster/8001/redis.conf
E	127.0.0.1	8002	from	/	/usr/local/redis-cluster/8002/redis.conf
F	127.0.0.1	8003	from	/	/usr/local/redis-cluster/8003/redis.conf

Based on the previous plan, you can run the following command to create a directory for storing the startup configuration file of each node.

Copymkdir /usr/local/redis-cluster
cd redis-cluster
mkdir -p 7001 7002 7003 8001 8002 8003
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Run the following commands in sequence to go to the Redis source package directory and copy the default configuration file Redis.

Copycd /usr/local/redis-5.0.3 cp redis.conf /usr/local/redis-cluster/7001 cp redis.conf /usr/local/redis-cluster/7002 cp  redis.conf /usr/local/redis-cluster/7003 cp redis.conf /usr/local/redis-cluster/8001 cp redis.conf /usr/local/redis-cluster/8002 cp redis.conf /usr/local/redis-cluster/8003Copy the code

Next, you need to modify the configuration files for each node individually. The following are required parameters that are enabled or modified in the /usr/local/redis-cluster/7001/redis.conf configuration file of node A. For other nodes B, C, D, E, and F, refer to the modification, and modify the ports as planned for each node.

Pidfile /var/run/redis_7001. Pid # Set Redis instance PID file Daemonize yes # run Redis instance cluster-enabled yes # run Redis instance cluster-node-timeout 15000 Cluster-config-file nodes-701. conf # Set the configuration file path of the current node clusterCopy the code

You can start the six nodes in the cluster using the following set of commands.

Copy/usr/local/bin/redis-server /usr/local/redis-cluster/7001/redis.conf
/usr/local/bin/redis-server /usr/local/redis-cluster/7002/redis.conf
/usr/local/bin/redis-server /usr/local/redis-cluster/7003/redis.conf
/usr/local/bin/redis-server /usr/local/redis-cluster/8001/redis.conf
/usr/local/bin/redis-server /usr/local/redis-cluster/8002/redis.conf
/usr/local/bin/redis-server /usr/local/redis-cluster/8003/redis.conf
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Finally through the ps – ef | grep redis command confirmed that each node service is already running.

Copy[root@localhost bin]# ps -ef|grep redis root 5613 1 0 04:25 ? 00:00:00 /usr/local/bin/redis-server 127.0.0.1:7001 [cluster] root 5650 1 0 04:26? 00:00:00 /usr/local/bin/redis-server 127.0.0.1:7002 [cluster] root 5661 1 0 04:26? 00:00:00 /usr/local/bin/redis-server 127.0.0.1:7003 [cluster] root 5672 1 0 04:27? 00:00:00 /usr/local/bin/redis-server 127.0.0.1:8001 [cluster] root 5681 1 0 04:27? 00:00:00 /usr/local/bin/redis-server 127.0.0.1:8002 [cluster] root 5690 1 0 04:27? 00:00:00 /usr/local/bin/redis-server 127.0.0.1:8003 [cluster] root 5731 1311 0 04:28 PTS /0 00:00:00 grep --color=auto redisCopy the code

The above output shows that the six nodes planned above are started successfully.

Node to shake hands

Although cluster support is enabled for the above six nodes, they are not trusted or connected by default. Node handshake is the creation of links between nodes (each node is connected to other nodes) to form a complete grid, or cluster.

The command for node handshake is as follows:

Copycluster meet ip port
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But to create a cluster, you don’t need to send all the cluster meet commands needed to form a full grid. As long as enough cluster meet messages can be sent so that each node can reach each other through a series of known nodes, the missing links will be created automatically.

For example, if we connect node A to node B and B to C via cluster meet, A and C will find the handshake and create the link themselves.

The six nodes we created can be connected to node A through redis- CLI to execute the following five commands to complete the handshake. In the production environment, IP 127.0.0.1 needs to be replaced with an external IP address.

Copycluster meet 127.0.0.1 7002
cluster meet 127.0.0.1 7003
cluster meet 127.0.0.1 8001
cluster meet 127.0.0.1 8002
cluster meet 127.0.0.1 8003
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If the preceding command is executed normally, the following output is displayed:

Copy[root@localhost bin]# /usr/local/bin/redis-cli -p 7001
127.0.0.1:7001> cluster meet 127.0.0.1 7002
OK
127.0.0.1:7001> cluster meet 127.0.0.1 7003
OK
127.0.0.1:7001> cluster meet 127.0.0.1 8001
OK
127.0.0.1:7001> cluster meet 127.0.0.1 8002
OK
127.0.0.1:7001> cluster meet 127.0.0.1 8003
OK
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You can run the Cluster Nodes command to check the link status between nodes. I randomly found two nodes B and F to test, and the output results are as follows.

Copy[root@localhost /]# /usr/local/bin/redis-cli -p 7002 cluster nodes 61e8c4ed8d1ff2a765a4dd2c3d300d8121d26e12 127.0.0.1: master 7001 @ 17001-0 1552220691885 4 connected a8a41694f22977fda78863bdfb3fc03dd1fab1bd 127.0.0.1:8002 @ 18002 Master - 0 1552220691000 5 connected 51987 c4b5530c81f2845bb9d521daf6d3dce3659 127.0.0.1: master 8001 @ 18001-0 1552220690878 3 connected 1 b4b3741945d7fed472a1324aaaa6acaa1843ccb 127.0.0.1:7002 @ 17002 myself, master 1552220690000-0 1 connected 19147 f56e679767bcebb8653262ff7f56ca072a8 127.0.0.1:7003 @ 17003 master - 0 1552220691000 2 connected Ed6fd72e61b747af3705b210c7164bc68739303e 127.0.0.1:8003 @ 18003 master - 0, 1552220690000 connected root @ localhost / # / usr/local/bin/redis - cli - p 8002 cluster nodes 1 b4b3741945d7fed472a1324aaaa6acaa1843ccb 127.0.0.1: master 7002 @ 17002-0 1552220700255 1 connected ed6fd72e61b747af3705b210c7164bc68739303e 127.0.0.1:8003 @ 18003 master - 0, 1552220703281 Connected 19147 f56e679767bcebb8653262ff7f56ca072a8 127.0.0.1:7003 @ 17003 master - 0 1552220700000 2 connected A8a41694f22977fda78863bdfb3fc03dd1fab1bd 127.0.0.1:8002 @ 18002 myself, master 1552220701000-0 5 connected 61 e8c4ed8d1ff2a765a4dd2c3d300d8121d26e12 127.0.0.1:7001 @ 17001 master - 0 1552220702275 4 connected 51987 c4b5530c81f2845bb9d521daf6d3dce3659 127.0.0.1:8001 @ 18001 master - 0 1552220701265 3 connectedCopy the code

It can be seen that nodes B and F have been linked to the other five nodes respectively.

At this point, the node handshake is complete.

Distribution of slot

At this time, the Redis cluster is not online. You can run the cluster info command on any node to check the running status of the cluster.

Copy[root@localhost ~]# /usr/local/bin/redis-cli -p 7001 cluster info
cluster_state:fail
......
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Cluster_state :fail indicates that the cluster is offline. Because a cluster cannot go live until slots (hash slots, as mentioned in the first section of this article) are assigned to all the primary nodes in the cluster.

The commands for assigning slots are as follows:

Copycluster addslots slot [slot ...]
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Based on the pre-planning, this step requires using the Cluster addslots command to manually allocate 16,384 hash slots roughly equally to primary nodes A, B, and C.

Copy/usr/local/bin/redis-cli -p 7001 cluster addslots {0.. 5461} /usr/local/bin/redis-cli -p 7002 cluster addslots {5462.. 10922} /usr/local/bin/redis-cli -p 7003 cluster addslots {10923.. 16383}Copy the code

After the preceding three commands are executed, you can view some running parameters of the current cluster again.

Copy[root@localhost ~]# /usr/local/bin/redis-cli -p 7001 cluster info cluster_state:ok cluster_slots_assigned:16384 cluster_slots_ok:16384 cluster_slots_pfail:0 cluster_slots_fail:0 cluster_known_nodes:6 cluster_size:3 cluster_current_epoch:5 cluster_my_epoch:4 cluster_stats_messages_ping_sent:11413 cluster_stats_messages_pong_sent:10509  cluster_stats_messages_meet_sent:11 cluster_stats_messages_sent:21933 cluster_stats_messages_ping_received:10509 cluster_stats_messages_pong_received:10535 cluster_stats_messages_received:21044Copy the code

Cluster_state: OK indicates that the Redis cluster is online successfully.

A master-slave replication

The Redis cluster is successfully online, but the primary node has not been assigned a secondary node. If one node fails, the whole cluster will hang and the high availability will not be achieved.

You need to use the cluster replicate command to manually configure the primary node for the secondary node.

Cluster replication commands are as follows:

Copycluster replicate node-id
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Each node in the cluster node – id can be used to cluster nodes command to view, the following output 1 b4b3741945d7fed472a1324aaaa6acaa1843ccb is the master node B node – id.

Copy[root@localhost /]# /usr/local/bin/redis-cli -p 8002 cluster nodes1 b4b3741945d7fed472a1324aaaa6acaa1843ccb 127.0.0.1:7002 @ 17002 master 1552220700255-0 1 connected Ed6fd72e61b747af3705b210c7164bc68739303e 127.0.0.1:8003 @ 18003 master - 0, 1552220703281 connected 19147 f56e679767bcebb8653262ff7f56ca072a8 127.0.0.1:7003 @ 17003 master - 0 1552220700000 2 connected A8a41694f22977fda78863bdfb3fc03dd1fab1bd 127.0.0.1:8002 @ 18002 myself, master 1552220701000-0 5 connected 61 e8c4ed8d1ff2a765a4dd2c3d300d8121d26e12 127.0.0.1:7001 @ 17001 master - 0 1552220702275 4 connected 51987 c4b5530c81f2845bb9d521daf6d3dce3659 127.0.0.1:8001 @ 18001 master - 0 1552220701265 3 connectedCopy the code

According to the planning in advance, A master D slave; B primary E secondary; C primary F secondary. Run the following commands to specify primary nodes for secondary nodes D, E, and F so that the cluster can automatically complete the primary/secondary replication.

Copy/usr/local/bin/redis-cli -p 8001 cluster replicate 61e8c4ed8d1ff2a765a4dd2c3d300d8121d26e12 /usr/local/bin/redis-cli  -p 8002 cluster replicate 1b4b3741945d7fed472a1324aaaa6acaa1843ccb /usr/local/bin/redis-cli -p 8003 cluster replicate 19147f56e679767bcebb8653262ff7f56ca072a8Copy the code

When this command is executed successfully, we have set up a Redis cluster manually.

Finally, take a look at the node information in the cluster.

Copy[root@localhost ~]# /usr/local/bin/redis-cli -p 8002 cluster nodes 1b4b3741945d7fed472a1324aaaa6acaa1843ccb 127.0.0.1: master 7002 @ 17002-0, 1552233328337 1 connected ed6fd72e61b747af3705b210c7164bc68739303e. 5462-10922 127.0.0.1:8003 @ 18003 slave f56e679767bcebb8653262ff7f56ca072a8 0 19147 1552233327000 2 connected 19147 f56e679767bcebb8653262ff7f56ca072a8 127.0.0.1:7003 @ 17003 master - 0 1552233325000 2 connected. 10923-16383 A8a41694f22977fda78863bdfb3fc03dd1fab1bd 127.0.0.1:8002 @ 18002 myself, slave 1 b4b3741945d7fed472a1324aaaa6acaa1843ccb 0 1552233327000 5 connected 61 e8c4ed8d1ff2a765a4dd2c3d300d8121d26e12 127.0.0.1:7001 @ 17001 master - 0, 1552233327327 Connected a scale of 0-5461 to 51987 c4b5530c81f2845bb9d521daf6d3dce3659 127.0.0.1:8001 @ 18001 slave 61e8c4ed8d1ff2a765a4dd2c3d300d8121d26e12 0 1552233326320 4 connectedCopy the code

Automatic construction

A cluster management tool, redis-trib.rb, has been released since Redis 3.0, integrated in the SRC directory of the Redis source package. It encapsulates Redis cluster command, simple and convenient to use.

However, redis-trib.rb was developed in Ruby by redis authors, so you need to install the Ruby environment on your machine before using this tool. As the authors may be aware of this problem, Redis 5.0 has integrated the tool into Redis – CLI starting with the –cluster parameter, where the create command can be used to create clusters.

Start node

Before using the cluster management tool to build a cluster, you need to start each node. For details about how to start a node, see “Manually Create a node” – “Start a Node”.

The cluster management tool is set up

If you have versions 3. X and 4. X of Redis installed, you can build with Redis -trib.rb, but you will need to install the Ruby environment.

Start by installing the Ruby environment and other dependencies with Yum.

Copyyum -y install ruby ruby-devel rubygems rpm-build
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Confirm the installed version.

Copy[root@localhost redis-cluster]# ruby -v
ruby 2.0.0p648 (2015-12-16) [x86_64-linux]
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Run the redis-trib.rb script to set up the cluster.

Copy/usr/local/redis-5.0.3/src/redis-trib.rb create --replicas 1 127.0.0.1:7001 127.0.0.1:7002 127.0.0.1:7003 127.0.0.1:8001 127.0.0.1:8002 127.0.0.1:8003
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However, the Redis version used in this paper is 5.0.3, so I can directly use Redis -cli –cluster create command to set up, as shown below.

Copy/usr/local/bin/redis-cli --cluster create 127.0.0.1:7001 127.0.0.1:7002 127.0.0.1:7003 127.0.0.1:8001 127.0.0.1:8002 127.0.0.1:8003-1 - cluster - replicasCopy the code

The primary node comes first, followed by the secondary node. The –cluster-replicas parameter specifies the number of secondary nodes in a primary node. For example, –cluster-replicas 1 indicates that each primary node has one secondary node.

If the command is successfully executed, the following information is displayed:

Copy[root@localhost bin]# redis-cli --cluster create 127.0.0.1:7001 127.0.0.1:7002 127.0.0.1:7003 127.0.0.1:8001 127.0.0.1:8002 127.0.0.1:8003 --cluster-replicas 1 >> Performing hash slots Allocation on 6 nodes... Master[0] -slots 0-5460 Master[1] -slots 5461-10922 Master[2] -slots 10923-16383 Adding Replica 127.0.0.1:8001 To 127.0.0.1:7001 Adding Replica 127.0.0.1:8002 to 127.0.0.1:7002 Adding Replica 127.0.0.1:8003 to 127.0.0.1:7003 >> Trying to optimize slaves allocation for anti-affinity [WARNING] Some slaves are in the same host as their master M: 32 f9819fc7d561bfa2b7189182200e86d9901b8a 127.0.0.1:7001 slots: [0-5460] (5461 slots) master M: Cca0fbfa374bc175d481e68ee9ed13b65453e967 127.0.0.1:7002 slots: [5461-10922] (5462 slots) master M: 964 cfa1c2dcfe36b6d3c63637f0d57ccb568354e 127.0.0.1:7003 slots: [10923-16383] (5461 slots) master S: 1 b47b9e6e7a79523579b8d2ddcd5e708583ed317 127.0.0.1:8001 replicates 32 f9819fc7d561bfa2b7189182200e86d9901b8a S: Aba9330f3e70f26a8af4ced1b672fbcc7bc62d78 127.0.0.1:8002 replicates cca0fbfa374bc175d481e68ee9ed13b65453e967 S: 254 db0830cd764e075aa793144572d5fa3a398f0 127.0.0.1:8003 964 cfa1c2dcfe36b6d3c63637f0d57ccb568354e replicates Can I set the above configuration? (type 'yes' to accept): yes >> Nodes configuration updated >> Assign a different config epoch to each node >> Sending CLUSTER MEET messages to join the cluster Waiting for the cluster to join ... >> Performing Cluster Check (using node 127.0.0.1:7001) M: 32 f9819fc7d561bfa2b7189182200e86d9901b8a 127.0.0.1:7001 slots: [0-5460] (5461 slots) master 1 additional up (s) s: Aba9330f3e70f26a8af4ced1b672fbcc7bc62d78 127.0.0.1:8002 slots: (0 slots) slave replicates cca0fbfa374bc175d481e68ee9ed13b65453e967 S: 1 b47b9e6e7a79523579b8d2ddcd5e708583ed317 127.0.0.1:8001 slots: (0 slots) slave replicates 32f9819fc7d561bfa2b7189182200e86d9901b8a S: 254 db0830cd764e075aa793144572d5fa3a398f0 127.0.0.1:8003 slots: (0 slots) slave replicates 964cfa1c2dcfe36b6d3c63637f0d57ccb568354e M: Cca0fbfa374bc175d481e68ee9ed13b65453e967 127.0.0.1:7002 slots: [5461-10922] (5462 slots) master 1 additional up (s) M: 964 cfa1c2dcfe36b6d3c63637f0d57ccb568354e 127.0.0.1:7003 slots: [10923-16383] (5461 slots) master 1 additional up (s) [OK] All nodes agree about slots configuration. >> Check for open slots... >> Check slots coverage... [OK] All 16384 slots covered.Copy the code

OK, setup complete! One command.

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Redis cluster building is not working this time! You came to me ~~

Introduction to the Redis cluster

Download & install Redis

Set up the Redis cluster

Manual setup

Start node

Node to shake hands

Distribution of slot

A master-slave replication

Automatic construction

Start node

The cluster management tool is set up

Redis cluster building is not working this time! You came to me ~~

Introduction to the Redis cluster

Download & install Redis

Set up the Redis cluster

Manual setup

Start node

Node to shake hands

Distribution of slot

A master-slave replication

Automatic construction

Start node

The cluster management tool is set up

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