NLB limits - Server Load Balancer - Alibaba Cloud Documentation Center

This topic describes the limits on Network Load Balancer (NLB), including resource quotas.

Resource quotas

Item	Default value	Adjustable
NLB instance
Maximum number of NLB instances that each Alibaba Cloud account can have in a region	60	You can request a quota increase by using one of the following methods: Go to the Quota Management page of the Server Load Balancer (SLB) console, click the NLB tab, and then increase the quota nlb_quota_loadbalancers_num. Log on to the Quota Center console and request a quota increase. For more information, see Request a quota increase.
Maximum number of elastic container instances that can be specified as backend servers for each NLB instance	1,600	No
Maximum number of Elastic Compute Service (ECS) instances, elastic network interfaces (ENIs), or IP addresses that can be specified as backend servers for each NLB instance	400	You can request a quota increase by using one of the following methods: Go to the Quota Management page of the SLB console, click the NLB tab, and then increase the quota nlb_quota_loadbalancer_noeci_servers_num. Log on to the Quota Center console and request a quota increase. For more information, see Request a quota increase.
Maximum number of listeners that can be added to each NLB instance	50	You can request a quota increase by using one of the following methods: Go to the Quota Management page of the SLB console, click the NLB tab, and then increase the quota nlb_quota_loadbalancer_listeners_num. Log on to the Quota Center console and request a quota increase. For more information, see Request a quota increase.
Maximum number of additional certificates that can be added to each NLB instance, excluding the default certificate	25	You can request a quota increase by using one of the following methods: Go to the Quota Management page of the SLB console, click the NLB tab, and then increase the quota nlb_quota_loadbalancer_certificates_num. Log on to the Quota Center console and request a quota increase. For more information, see Request a quota increase.
Server group
Maximum number of NLB server groups that each Alibaba Cloud account can have in a region	3,000	No
Maximum number elastic container instances that can be added to each server group	1,600	No
Maximum number of ECS instances, ENIs, or IP addresses that can be added to each server group	400	You can request a quota increase by using one of the following methods: Go to the Quota Management page of the SLB console, click the NLB tab, and then increase the quota nlb_quota_servergroup_noeci_servers_num. Log on to the Quota Center console and request a quota increase. For more information, see Request a quota increase.
Maximum number of times that a backend server (including a backend server of the IP type) can be added to a server group	200	You can request a quota increase by using one of the following methods: Go to the Quota Management page of the SLB console, click the NLB tab, and then increase the quota nlb_quota_server_added_num. Log on to the Quota Center console and request a quota increase. For more information, see Request a quota increase.
Maximum number of times that each NLB server group can be associated with a listener	50	You can request a quota increase by using one of the following methods: Go to the Quota Management page of the SLB console, click the NLB tab, and then increase the quota nlb_quota_servergroup_attached_num. Log on to the Quota Center console and request a quota increase. For more information, see Request a quota increase.
Security policy
Maximum number of custom security policies that each Alibaba Cloud account can have in a region	50	No
Security group
Maximum number of security groups to which each NLB instance can be added	The maximum number of security groups and security group rules that can be associated with an NLB instance are subject to ECS security group quotas: Maximum number of security groups that can be associated with an NLB instance = Quota for security groups associated with an ENI - 1 (taken by the managed security group for the NLB instance) Maximum number of security group rules that can be associated with an NLB instance = Quota for security group rules associated with an ENI - Number of rules in the managed security group for the NLB instance

Other limits

If the number of backend server groups drops to a low number, and a single client visits the domain name of the NLB instance whose backend servers have client IP address preservation enabled, or accesses the virtual IP addresses or elastic IP addresses (EIPs) of both the NLB instance and a Classic Load Balancer (CLB) instance that share the same backend servers, conflicts may arise in source IP addresses, source ports, destination IP addresses, destination ports, and transmission protocols.
The private virtual IP addresses to which the domain name of an NLB instance is resolved support probes. However, you need to enable ICMP when you configure Cloud Firewall or access control lists. Otherwise, the NLB domain name may fail to be resolved to the virtual IP addresses due to probe failures.
If a UDP listener is associated with a server group that uses ID hashing algorithms other than QUIC, such as round robin and weighted round robin, the backend servers must not use stateful UDP services, such as QUIC. If the backend servers need to use stateful UDP services, we recommend that the server groups use QUIC-based ID hashing.
If Client IP Reservation is disabled for a server group (of either the server or the IP address type), the NLB node in each zone supports up to 60,000 concurrent connections to a single backend server within the server group. If the number of concurrent connections exceeds this limit, NLB auto scales its local IP addresses to prevent connection failures. The NLB node in each zone can use up to eight local IP addresses. When this limit is reached, the NLB node in each zone supports up to 250,000 concurrent connections to each backend server. Ensure the vSwitch to which NLB is connected has a sufficient number of available IP addresses for NLB auto-scaling.
Note
Enable Client IP Reservation to avoid such circumstances. Alternatively, add more backend servers to the server group.