Server Load Balancer provides an API to query the default limits of an SLB instance. For more information, see Query Quota-DescribeSlbQuotas.

Resource Default limits
Limits on SLB instances
Number of SLB instances per account 60
Number of times that an ECS instance can be added to SLB instances 50
Number of backend servers that can be added to an SLB instance 200
Number of listeners that can be added to an SLB instance 50
Number of domain /URL forwarding rules that can be added to a Layer-7 listener 20
Number of domain name extensions that an HTTPS listener can create 3
Number of API calls per an AccessKey 5,000 times/day
Frontend/backend port range used by a listener 1-65535
Frontend/backend port range used by a listener (Financial Cloud) 80, 443, 2800-3300, 5000-10000, 13000-14000
Limits on certificates
Number of server certificates that can be uploaded in a region 1,000
Number of CA certificates that can be uploaded in a region 100
Limits on access control lists
Number of access control lists that can be created in a region 50
Number of access control entries that can be added to an access control list 300
Number of IP entries that can be added to an access control list in an API call 50
Number of times that an access control list can be added to listeners 50