This topic provides answers to frequently asked questions about how to connect to PolarDB clusters.

  • Am I charged for data traffic if my application uses a public endpoint to connect to a PolarDB cluster?

    No, you are not charged for data traffic that is incurred by using public endpoints of PolarDB clusters.

  • What is the maximum number of single-node cluster endpoints that I can create in a cluster?

    You can create up to six custom cluster endpoints for a cluster. The custom cluster endpoints can be single-node cluster endpoints. For more information about how to create a single-node cluster endpoint, see Create a custom cluster endpoint.

    Warning If you create a single-node cluster endpoint for a read-only node and the read-only node fails to run as expected, the single-node cluster endpoint may be unavailable for up to 1 hour. We recommend that you do not create single-node cluster endpoints in your production environment.
  • If a single-node cluster endpoint is created for a read-only node, can the read-only node be used as the new primary node after a failover?

    The read-only node for which a single-node cluster endpoint is created cannot be automatically used as the new primary node after a failover. However, you can manually promote the read-only node as the new primary node. For more information, see Automatic failover and manual failover.

  • What is the maximum number of cluster endpoints that can be created for a cluster?

    A cluster can contain a maximum of seven cluster endpoints. One cluster endpoint is the default cluster endpoint and the other endpoints are custom cluster endpoints.

  • Can I modify a cluster endpoint?

    Yes, you can modify the default cluster endpoint and custom cluster endpoints. For more information, see Modify an endpoint.

  • Can I delete a cluster endpoint?

    Yes, you can delete only custom cluster endpoints. You cannot delete the default cluster endpoint. For more information, see Delete an endpoint.

  • Why am I unable to connect an ECS instance to the internal endpoint of a PolarDB cluster?
    To connect an ECS instance to the internal endpoint of a PolarDB cluster, the following requirements must be met:
    • The ECS instance and PolarDB cluster are deployed in the same region.
    • The ECS instance and PolarDB cluster use the same network type. If they use the VPC network type, they must be on the same VPC. If the ECS instance and PolarDB cluster are not on the same VPC, you can Use Basic Edition transit routers to connect VPCs in the same region.
    • The private IP address of the ECS instance is added to the whitelist of the PolarDB cluster.
    If the PolarDB cluster is on a VPC while the ECS instance is on the classic network, you can use one of the following solutions to connect the ECS instance to the internal endpoint of the PolarDB cluster:
    • Solution 1: Migrate the ECS instance from the classic network to the VPC where the PolarDB cluster is deployed. For more information, see Migrate an ECS instance from a classic network to a VPC.
      Note If the ECS instance also needs to access other resources on the classic network, do not migrate the ECS instance. Otherwise, the ECS instance cannot access the classic network.
    • Solution 2: use the ClassicLink feature to connect the classic network to the VPC network.
  • Why am I unable to connect an ECS instance to the public endpoint of a PolarDB cluster?
    You can perform the following steps:
    1. Check whether the endpoint, port, account, and password for the connection are correct. If yes, check whether the IP whitelist of the PolarDB cluster is correct.
    2. Add 0.0.0.0/0 to the IP whitelist of the PolarDB cluster. After the cluster is connected, execute the SHOW processlist statement to obtain the egress public IP address of the cluster. Add it to the whitelist of the cluster and delete 0.0.0.0/0 from the whitelist.
      Note 0.0.0.0/0 in the IP whitelist indicates that all sources are allowed to access the cluster. Do not add 0.0.0.0/0 to the IP whitelist of the cluster unless it is necessary.
  • Why am I unable to connect an ECS instance to a PolarDB cluster?
    An ECS instance can be connected to a PolarDB cluster over the internal network when the following requirements are met: using the same account, in the same region, and on the same VPC. VPC isolation exists for different accounts or across different regions. PolarDB Common reasons why an ECS instance cannot connect to a PolarDB cluster: