Notes and Constraints

You can create dedicated and shared load balancers on ELB console. This section describes the quotas and restrictions that apply to ELB resources.

Quotas put limits on the number or amount of resources, such as the maximum number of ECSs or EVS disks that you can create.

Table 1 lists the default quotas of ELB resources. You can view your quotas by referring to How Do I View My Quotas?

If the existing resource quota cannot meet your service requirements, you can request an increase by referring to How Do I Apply for a Higher Quota?

**Table 1** ELB resource quotas
Resource	Description	Default Quota
Load balancers	Load balancers per account	50
Listeners	Listeners per account	100
Forwarding policies	Forwarding policies per account	500
Backend server groups	Backend server groups per account	500
Certificates	Certificates per account	120
Backend servers	Backend servers per account	500
Listeners per load balancer	Listeners that can be added to a load balancer	50
Forwarding policies per listener	Maximum number of forwarding policies that can be added to a listener	100

The quotas apply to a single account.

In addition to quotas described in ELB Resource Quotas, some other resources that you can use are also limited.

You can call APIs to query quotas of the resources described in Table 2 by referring to Querying Quotas.

**Table 2** Other quotas
Resource	Description	Default Quota
Forwarding rules per forwarding policy	Forwarding rules that can be added to a forwarding policy	10
Backend servers per backend server group	Backend servers that can be added to a backend server group	500
IP address group
IP address groups per load balancer	IP address groups per account	50
Listeners per IP address group	Listeners that can be associated with an IP address group	50
IP addresses per IP address group	IP addresses that can be added to an IP address group	300

Before creating a load balancer, you must plan its region, type, protocol, and backend servers. For details, see Preparations for Creating a Load Balancer.
The maximum size of data that a load balancer can forward:
- Layer 4 listeners: any
- Layer 7 listeners:
  - 10 GB (file size)
  - 32 KB (the total size of the HTTP request line and HTTP request header)

The listener of a dedicated load balancer can be associated with a maximum of 50 backend server groups.
A certificate can be associated with a maximum of 600 listeners.
SNI certificates
- Shared load balancers
  - An HTTPS listener can have up to 30 SNI certificates.
  - A certificate can have a maximum of 30 domain names. By default, all SNI certificates can have up to 30 domain names.
  - A domain name can contain a maximum of 100 characters, and the total length of all domain names cannot exceed 1,024 characters.
- Dedicated load balancers
  - An HTTPS listener can have up to 30 SNI certificates by default, but you can request an increase to 50.
  - A certificate can have a maximum of 100 domain names. By default, all SNI certificates can have up to 200 domain names.
  - A domain name can contain a maximum of 100 characters, and the total length of all domain names cannot exceed 10,000 characters.
Once set, the frontend protocol and port of the listener cannot be modified.

Forwarding policies can be configured only for HTTP and HTTPS listeners.
Forwarding policies must be unique.
A maximum of 100 forwarding policies can be configured for a listener. If the number of forwarding policies exceeds the quota, the excess forwarding policies will not be applied.
Forwarding conditions:
- If the advanced forwarding policy is not enabled, each forwarding rule has only one forwarding condition.
- If the advanced forwarding policy is enabled, each forwarding rule has up to 10 forwarding conditions.

**Table 3** Restrictions on forwarding policies
Load Balancer Type	Advanced Forwarding	Forwarding Rule	Action	Reference
Shared	Not supported	Domain name and path	Forward to another backend server group and Redirect to another listener	Forwarding Policy (Shared Load Balancers)
Dedicated	Disabled	Domain name and path	Forward to another backend server group and Redirect to another listener	Forwarding Policy (Dedicated Load Balancers)
Dedicated	Enabled	Domain name, path, HTTP request method, HTTP header, query string, cookie, and CIDR block	Forward to a backend server group, redirect to another listener, redirect to another URL, and return a specific response body.	Advanced Forwarding (Dedicated Load Balancers)

The backend protocol of the backend server group must match the frontend protocol of the listener as described in Table 4.

**Table 4** The frontend and backend protocol
Load Balancer Specification	Frontend Protocol	Backend Protocol
Network load balancing	TCP	TCP
Network load balancing	UDP	UDP QUIC
Application load balancing	HTTP	HTTP
Application load balancing	HTTPS	HTTP HTTPS

If Transfer Client IP Address is enabled, a server cannot serve as both a backend server and a client.
An ECS can be added as a backend server for a maximum of 800 times. If it is added to the same backend server group, the port must be unique.