Server Load Balancer:Modify configurations for an NLB instance

Use scenarios

The current zones for your NLB instance or the elastic IP addresses (EIPs) associated with your Internet-facing NLB instance do not match your business traffic.

Limitations

• For an NLB instance deployed in two or fewer zones, the number of zones cannot be reduced.

• For an Internet-facing NLB instance:

  • The EIPs associated with the instance for different zones must be of the same type.

  • You can associate with the NLB instance only pay-as-you-go (pay-by-data-transfer) EIPs that are not added to any Internet Shared Bandwidth. (After EIPs are associated with the NLB instance, you can then associate the NLB instance with an Internet Shared Bandwidth instance in the NLB console to save costs.)

  • Subscription or pay-as-you-go (pay-by-bandwidth) EIPs are not supported.

  • When the NLB instance is released, associated EIPs that are automatically assigned to it by the system will be released along with it, while EIPs that you created separately will be retained.

Billing impact

When you update the zones for an Internet-facing NLB instance, the EIPs that are associated with the instance may change. You are charged for the EIPs in use. For more information, see EIP billing overview.

Effective time

The new zones you set for an NLB instance immediately take effect. If the network latency is high, you may need to wait a few minutes.

Procedure

1. Log on to the NLB console.

2. In the top navigation bar, select the region.

3. On the Instances page:

   • Find the NLB instance and, in the Actions column, choose > Modify Zone/Subnet.

   • Alternatively, click the ID of the NLB instance. On the Instance Details tab, click Modify Zone/Subnet.

4. In the Modify Zone/Subnet dialog box:

   • To enable a zone, select its check box and select one vSwitch. For an Internet-facing NLB instance, assign one EIP for the zone. Then, click OK.

     Note

     If you select Purchase EIP, a pay-as-you-go (pay-by-data-transfer) BGP (Multi-ISP) EIP with basic DDoS protection is created by default.

   • To disable a zone, clear its check box, then click OK.

Zone status

Remove or restore a DNS record

1. Log on to the NLB console.

2. In the top navigation bar, select the region.

3. On the Instances page, click the ID of the NLB instance.

4. On the Instance Details tab, in the Zone section, perform the following operations based on your business requirements:

   • Remove the DNS record

     Find the zone whose DNS record you want to remove, click DNS Removed in the Actions column, confirm the impact in the dialog box, and then click I Understand The Impact. Continue To Remove The DNS Record.

     Note

     • This operation takes effect only for the current NLB instance. Other instances in the zone are not affected.

     • If you remove a DNS record, the A record that resolves the domain name of the NLB instance to the VIP of the zone is deleted. Proceed with caution.

     After the DNS record is removed, the status of the zone changes to DNS Removed and the health check on the VIP of the zone stops.

   • Restore the DNS record

     To restore the DNS record of a zone whose status is DNS Removed, click Restore The DNS Record in the Actions column, confirm the impact in the dialog box, and then click I Understand The Impact. Continue To Restore The DNS Record.

     Note

     After the zone is re-enabled, an A record that resolves the domain name of the NLB instance to the VIP of the zone is added. Traffic destined for the domain name of the NLB instance is forwarded by using the VIP of the zone.

     After the DNS record is restored, the status of the zone changes to Enabled and the health check on the VIP of the zone starts.

What determines the maximum bandwidth?

An Internet-facing NLB instance uses the EIP that is associated with it to access the Internet.

Depending on whether an NLB instance is associated with an Internet Shared Bandwidth instance, the maximum bandwidth for the NLB instance is calculated differently:

• Without Internet Shared Bandwidth: The maximum bandwidth the NLB instance can use in each zone is the maximum bandwidth for the EIP it uses for that zone.

  Important

  The maximum bandwidth for an EIP is only a reference value and is not a guaranteed service level agreement (SLA). Similarly, the sum of the maximum bandwidths for all EIPs associated with an NLB instance is also a reference value and not a guaranteed SLA.

  For example, your NLB instance is deployed in three zones, and is assigned with an EIP to use in each zone. Assume each of the EIPs is configured to use a 200 Mbit/s of bandwidth. If the infrastructure resources are insufficient, the actual maximum bandwidth that an EIP can reach may be less than 200 Mbit/s, and the over maximum bandwidth for the NLB instance cannot reach 600 Mbit/s.

• With Internet Shared Bandwidth: All EIPs for the NLB instance share bandwidth resources. The upper limit for a single EIP no longer work. All resources allocated are managed by the Internet Shared Bandwidth instance. The maximum bandwidth for the Internet Shared Bandwidth instance is the maximum bandwidth for the NLB instance.

  Important

  Similarly, the maximum bandwidth for an Internet Shared Bandwidth instance is only a reference value and not a guaranteed SLA.

How do I increase the maximum bandwidth?

1. If the maximum bandwidth for an EIP is less than the supported maximum value of 200 Mbit/s, you can upgrade the EIP to increase its maximum bandwidth.

2. If the maximum bandwidth is still insufficient, you can use one of the following methods to increase it for the NLB instance:

   1. Add more zones for the NLB instance: Within regions supporting multi-zone deployment, you can add more zones for an NLB instance to use additional EIPs. Consequently, the overall maximum bandwidth for the NLB instance will be increased . This method applies if you want to save on Internet data transfer costs and your services experience large traffic fluctuations.

   2. Associate the NLB instance with an Internet Shared Bandwidth instance: An NLB instance can be associated with only one EIP per zone. Therefore, the theoretical maximum bandwidth for an NLB instance is calculated as follows: Theoretical maximum bandwidth for an NLB instance = Maximum number of zones × Theoretical maximum bandwidth for an EIP (200 Mbit/s). If your services require more than this theoretical maximum bandwidth for an NLB instance and you do not mind incurring additional costs, you can consider associating your NLB instance with an Internet Shared Bandwidth instance.

Possible causes for packet losses

• Different maximum bandwidth for each EIP: NLB evenly distributes traffic to its EIPs in the round-robin DNS way to ensure zone-disaster recovery. If EIPs in different zones have different maximum bandwidths, services may be affected when traffic is switched from an EIP with a high maximum bandwidth to an EIP with a low maximum bandwidth.

  For example, you purchase an NLB instance that is deployed in three zones, and the associated EIPs have maximum bandwidths of 200 Mbit/s, 200 Mbit/s, and 100 Mbit/s. Assume that the theoretical bandwidth values can be reached. When the traffic exceeds 300 Mbit/s, each EIP is allocated more than 100 Mbit/s of traffic. In this case, packet losses occur for traffic that is distributed to the EIP with a maximum bandwidth of 100 Mbit/s.

• Uneven traffic distribution: Even if you set the EIPs for an NLB instance to use the same maximum bandwidth, if a certain EIP receives extra traffic, for example, the client directly accesses the EIP not the domain name of your NLB instance, packet losses occur.

  For example, you set your NLB instance to use a 200, 200, and 100 Mbit/s of bandwidths in three different zones. Assume that the theoretical maximum bandwidth can be reached. Because the client accesses the EIP instead of the domain name of your NLB instance, which causes uneven traffic distribution, the actual bandwidth used by the three EIPs are 200, 100, and 0 Mbit/s, respectively. At this time, the client packets sent to the first EIP may be dropped.

• Insufficient backend service capabilities: Even with sufficient bandwidth for each EIP or the associated Internet Shared Bandwidth instance, if backend servers cannot promptly handle highly concurrent connections (indicated by high CPU usage, response delay, and TCP retransmission), packet losses still occur.

Configuration recommendations

• Ensure that the maximum bandwidth for each EIP or the associated Internet Shared Bandwidth instance is a bit larger than what your services require.

• Without Internet Shared Bandwidth:

  • Set all EIPs for an NLB instance to use the same maximum bandwidth. This prevents service unavailability caused by maximum bandwidth differences between zones when failover occurs.

  • Resolve the domain name of your NLB instance, instead of a particular EIP to your service domain name to avoid uneven traffic distribution.