What is the startup order for a MongoDB cluster?
The sequence of starting the MongoDB cluster is as follows:
- Start the configuration server: The configuration server is an important component of the MongoDB cluster, storing metadata information for the cluster. It is necessary to start the configuration server before launching any other nodes, and ensure that it is running properly.
- Start the shard server: The shard server is a data storage node in the MongoDB cluster. Before starting the shard server, make sure the config server has already been started and is running properly. The shard server can be started in any order, but it is usually recommended to start them based on the range of the shard key for better data distribution and load balancing.
- Start the router: The router, also known as the mongos process, is the query routing node in a MongoDB cluster. Before starting the router, ensure that the config server and at least one shard server are already started and running smoothly. The router routes client queries to the correct shard server and returns the aggregated results to the client.
- Start the replica set: It is essential to ensure that the primary node in the replica set is up and running before starting any secondary nodes. The nodes in the replica set will conduct an election to select a primary node to handle write operations and query requests.
In conclusion, the proper startup sequence for a MongoDB cluster is to first start the configuration servers, followed by the shard servers, then the routers, and finally the replica sets.
