Register targets with your target group - Elastic Load Balancing

Register targets with your target group

When your target is ready to handle requests, you register it with one or more target groups. You can register targets by instance ID or by IP address. The load balancer starts routing requests to the target as soon as the registration process completes and the target passes the initial health checks. It can take a few minutes for the registration process to complete and health checks to start. For more information, see Health checks for your target groups.

If demand on your currently registered targets increases, you can register additional targets in order to handle the demand. If demand on your registered targets decreases, you can deregister targets from your target group. It can take a few minutes for the deregistration process to complete and for the load balancer to stop routing requests to the target. If demand increases subsequently, you can register targets that you deregistered with the target group again. If you need to service a target, you can deregister it and then register it again when servicing is complete.

When you deregister a target, Elastic Load Balancing waits until in-flight requests have completed. This is known as connection draining. The status of a target is draining while connection draining is in progress. After deregistration is complete, status of the target changes to unused. For more information, see Deregistration delay.

If you are registering targets by instance ID, you can use your load balancer with an Auto Scaling group. After you attach a target group to an Auto Scaling group and the group scales out, the instances launched by the Auto Scaling group are automatically registered with the target group. If you detach the load balancer from the Auto Scaling group, the instances are automatically deregistered from the target group. For more information, see Attaching a Load Balancer to Your Auto Scaling Group in the Amazon EC2 Auto Scaling User Guide.

Target security groups

When you register EC2 instances as targets, you must ensure that the security groups for these instances allow traffic on both the listener port and the health check port.

Limits

  • Network Load Balancers do not have associated security groups. Therefore, the security groups for your targets must use IP addresses to allow traffic from the load balancer.

  • You cannot allow traffic from clients to targets through the load balancer using the security groups for the clients in the security groups for the targets. Use the client CIDR blocks in the target security groups instead.

Inbound
Source Protocol Port Range Comment

Client IP addresses

target

target

Allow client traffic (instance target type)

VPC CIDR

target

target

Allow client traffic (ip target type)

VPC CIDR

health check

health check

Allow health check traffic from the load balancer

If you register targets by IP address and do not want to grant access to the entire VPC CIDR, you can grant access to the private IP addresses used by the load balancer nodes. There is one IP address per load balancer subnet. To find these addresses, use the following procedure.

To find the private IP addresses to whitelist

  1. Open the Amazon EC2 console at https://console.aws.amazon.com/ec2/.

  2. In the navigation pane, choose Network Interfaces.

  3. In the search field, type the name of your Network Load Balancer. There is one network interface per load balancer subnet.

  4. On the Details tab for each network interface, copy the address from Primary private IPv4 IP.

Network ACLs

When you register EC2 instances as targets, you must ensure that the network ACLs for the subnets for your instances allow traffic on both the listener port and the health check port. The default network access control list (ACL) for a VPC allows all inbound and outbound traffic. If you create custom network ACLs, verify that they allow the appropriate traffic.

The network ACLs associated with the subnets for your instances must allow the following traffic for an internet-facing load balancer.

Inbound
Source Protocol Port Range Comment

Client IP addresses

listener

listener

Allow client traffic (instance target type)

VPC CIDR

listener

listener

Allow client traffic (ip target type)

VPC CIDR

health check

health check

Allow health check traffic from the load balancer

Outbound
Destination Protocol Port Range Comment

Client IP addresses

listener

listener

Allow responses to clients (instance target type)

VPC CIDR

listener

listener

Allow responses to clients (ip target type)

VPC CIDR

health check

1024-65535

Allow health check traffic

The network ACLs associated with the subnets for your load balancer must allow the following traffic for an internet-facing load balancer.

Inbound
Source Protocol Port Range Comment

Client IP addresses

listener

listener

Allow client traffic (instance target type )

VPC CIDR

listener

listener

Allow client traffic (ip target type )

VPC CIDR

health check

1024-65535

Allow health check traffic

Outbound
Destination Protocol Port Range Comment

Client IP addresses

listener

listener

Allow responses to clients (instance target type )

VPC CIDR

listener

listener

Allow responses to clients (ip target type )

VPC CIDR

health check

health check

Allow health check traffic

VPC CIDR

health check

1024-65535

Allow health check traffic

For an internal load balancer, the network ACLs for the subnets for your instances and load balancer nodes must allow both inbound and outbound traffic to and from the VPC CIDR, on the listener port and ephemeral ports.

Register or deregister targets

Each target group must have at least one registered target in each Availability Zone that is enabled for the load balancer.

The target type of your target group determines how you register targets with that target group. For more information, see Target type.

Requirements

  • You cannot register instances by instance ID if they use one of the following instance types: C1, CC1, CC2, CG1, CG2, CR1, G1, G2, HI1, HS1, M1, M2, M3, or T1.

  • You cannot register instances by instance ID if they are in a VPC that is peered to the load balancer VPC. You can register these instances by IP address.

  • If you register a target by IP address and the IP address is in the same VPC as the load balancer, the load balancer verifies that it is from a subnet that it can reach.

  • For UDP and TCP_UDP target groups, do not register instances by IP address if they reside outside of the load balancer VPC or if they use one of the following instance types: C1, CC1, CC2, CG1, CG2, CR1, G1, G2, HI1, HS1, M1, M2, M3, or T1. Targets that reside outside the load balancer VPC or use an unsupported instance type might be able to receive traffic from the load balancer but then be unable to respond.

Register or deregister targets by instance ID

An instance must be in the running state when you register it.

To register or deregister targets by instance ID

  1. Open the Amazon EC2 console at https://console.aws.amazon.com/ec2/.

  2. In the navigation pane, under LOAD BALANCING, choose Target Groups.

  3. Select the target group.

  4. Choose Targets, Edit.

  5. (Optional) For Registered instances, select any instances to be deregistered and choose Remove.

  6. (Optional) For Instances, select any running instances to be registered, modify the default instance port as needed, and then choose Add to registered.

  7. Choose Save.

Register or deregister targets by IP address

An IP address that you register must be from one of the following CIDR blocks:

  • The subnets of the VPC for the target group

  • 10.0.0.0/8 (RFC 1918)

  • 100.64.0.0/10 (RFC 6598)

  • 172.16.0.0/12 (RFC 1918)

  • 192.168.0.0/16 (RFC 1918)

To register or deregister targets by IP address

  1. Open the Amazon EC2 console at https://console.aws.amazon.com/ec2/.

  2. In the navigation pane, under LOAD BALANCING, choose Target Groups.

  3. Select the target group and choose Targets, Edit.

  4. To register IP addresses, choose the Register targets icon (the plus sign) in the menu bar. For each IP address, specify the network, Availability Zone, IP address, and port, and then choose Add to list. When you are finished specifying addresses, choose Register.

  5. To deregister IP addresses, choose the Deregister targets icon (the minus sign) in the menu bar. If you have many registered IP addresses, you might find it helpful to add a filter or change the sort order. Select the IP addresses and choose Deregister.

  6. To leave this screen, choose the Back to target group icon (the back button) in the menu bar.

Register or deregister targets using the AWS CLI

Use the register-targets command to add targets and the deregister-targets command to remove targets.