The MySQL cluster demands at least 4 nodes to be present for deploying a High Available MySQL database cluster. The typical configuration of any enterprise application is a 2 Node solution (Active-Standby mode or Active-Active Mode). The challenge lies in fitting the MySQL Clsuter Nodes in the 2 Nodes offering the application services and to make it work in that configuration with no single point of failure.
MySQL Cluster is a technology that enables clustering of in-memory databases in a “shared-nothing system”. By “shared-nothing” it is meant that each node has its own storage area. Note that the use of the shared storage mechanisms such as network file systems are not supported and recommended by MySQL. For High Availability there are at least 2 nodes on which the data is stored locally so that in case of one node failure the data is still accessible from the other available nodes. One of the data node acts as “Master” and the rest ones act as “Slaves”. These data nodes communicate with each other to replicate the data across the data nodes so that the change done on one node is also visible on rest of the nodes.
MySQL Cluster integrates the standard MySQL server with an in-memory clustered storage engine called NDBCluster (Network DataBase).
There are following actors in a MYSQL Cluster:
The figure below depicts these actors with the corresponding interactions
These are the clients/applications that actually use the MySQL Cluster. They connect through various methods such as MySQL C APIs, Java connectors. All of these clients connects to the SQL Nodes which in turn connects with the Data Nodes for accessing any data stored in the MySQL Cluster.
There is a special API provided by MySQL known as NDBAPI which directly connects with the Data Node bypassing the SQL Node. This increases the read/write operations performance significantly and is recommended to be used for high throughput applications which require very high rates for read/write.
This is a node that accesses the cluster data. In the case of MySQL Cluster, an SQL node is a traditional MySQL server that uses the NDBCLUSTER storage engine. An SQL node is a mysqld process started with the --ndbcluster and --ndb-connectstring options.
This type of node stores cluster data. There are as many data nodes as there are replicas, times the number of fragments. For example, with two replicas, each having two fragments, you need four data nodes. One replica is sufficient for data storage, but provides no redundancy; therefore, it is recommended to have 2 (or more) replicas to provide redundancy, and thus high availability.
The role of a management node is to manage the other nodes (Data Nodes, SQL Nodes and Client Nodes using NDBAPI). The Management node is the first node to be started in a MySQL Cluster before starting any other node. The functions it performs are:
11. How many physical servers are needed to create a minimum Cluster configuration? A: For evaluation and development purposes, you can run all nodes on a single host. For full redundancy and fault tolerance, you would need a minimum 6 x physical hosts: 2 x data nodes 2 x SQL/NoSQL Application Nodes 2 x Management Nodes Many users co-locate the Management and Application nodes which reduces the number of nodes to four.
11. How many physical servers are needed to create a minimum Cluster configuration?
A: For evaluation and development purposes, you can run all nodes on a single host. For full redundancy and fault tolerance, you would need a minimum 6 x physical hosts:
2 x data nodes
2 x SQL/NoSQL Application Nodes
2 x Management Nodes
Many users co-locate the Management and Application nodes which reduces the number of nodes to four.
The solution that was implemented for the challenges mentioned above.
Presented below is a sample configuration file for mysqld and Management Server.
Presented below is a sample rule
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