如何为连接ELB的EC2实例指定流量占比？含故障实例分流场景

Absolutely, you can set up custom traffic distribution like this with AWS Elastic Load Balancing—let’s break down how to handle your specific case and the general scenario of assigning traffic weights to EC2 instances behind an ELB.

Your Specific Scenario: 5% Traffic to Faulty Instance i3, 95% to i1 & i2 #

Yes, this is totally doable—though first, a quick note: this requires an ALB (Application Load Balancer) or NLB (Network Load Balancer). Classic Load Balancers don’t support weighted traffic distribution, so you’ll need to migrate to ALB/NLB if you’re still using the classic version.

Here’s how to configure the weights:

• Make sure all three EC2 instances are registered in the same target group attached to your ALB/NLB.
• Head to the AWS EC2 Console, navigate to Target Groups under the Load Balancing section, and select your target group.
• Go to the Targets tab—you’ll see a "Weight" column for each instance (default is 1 for equal distribution).
• Set weights to match your desired ratio:
  • Since you want 5% to i3 and 95% split between i1 and i2, use relative weights that add up to a total where i3’s share is ~5%. For example:
    • i3: 1 (accounts for 1/(1+9+10) = 5% of total traffic)
    • i1: 9 (45% of total)
    • i2: 10 (50% of total)
  • Weights are relative, so you can scale up the numbers if you prefer cleaner integers (e.g., i3=2, i1=18, i2=20—same ratio, same traffic split).
• Save your changes, and the LB will immediately start routing traffic according to the new weights.

Critical Note About Faulty Instances #

If i3 is marked unhealthy by the LB’s health checks, it won’t receive any traffic even with a weight set. If you specifically want to send traffic to the faulty instance, you’ll need to either:

• Temporarily disable health checks for the target group (not recommended for production, but useful for testing), or
• Manually override i3’s health status to "healthy" in the target group settings.

General Method: Assign Custom Traffic Ratios to All EC2 Instances #

For any scenario where you want to define exact traffic shares for instances behind an ALB/NLB, follow these steps:

1. Confirm your LB type: Only ALBs and NLBs support weighted target groups. Classic LBs don’t offer this feature.
2. Access your target group: In the AWS EC2 Console, go to Target Groups under Load Balancing, select the group associated with your LB.
3. Adjust target weights:
   • Navigate to the Targets tab.
   • Click the weight value for each instance to edit it. Weights must be integers between 0 and 256 (a weight of 0 means no traffic goes to that instance).
   • Set weights based on your desired ratio. For example:
     • If you want instance A to get 60%, B to get 30%, C to get 10%, use weights 6, 3, 1 (total 10, so each weight maps directly to 10x the percentage) or 60, 30, 10 (total 100, direct percentage mapping).
4. Verify distribution: Use CloudWatch metrics for your target group (check RequestCountPerTarget) to confirm traffic is being routed as expected.

内容的提问来源于stack exchange，提问作者Muhammad Sultan