Availability Zone ap-northeast-1b cannot be associated with a load balancer

Question

I'm trying to create cluster with ECS (Fargate) with nginx definition from Get Started button. But it becomes with following error message.

The following Availability Zones ap-northeast-1b cannot be associated with a load balancer. Please try a different Availability Zone.

All other VPC and subnets are created successfully, but only ALB cause error. When I try to create cluster without ALB, it works.

I also tried to create subnets (in ap-northeast-1a and ap-northeast-1b) and ALB by hand for verification, and it does show error when ALB is set to associate to ap-notheast-1b subnet.

How can this happen? And what can I do for Get Started nginx template with ALB to work fine?

Answer 1

I came across the same error but when creating a CloudFormation stack from a template. The error I got was similar:

Creating load balancer failed Reason: 
The following Availability Zones ap-northeast-1a cannot be associated with a load balancer. 
Please try a different Availability Zone. (Service: AmazonElasticLoadBalancing; 
Status Code: 400; 
Error Code: ValidationError; 

I could not find any official AWS documentation on the topic. Apparently some availability zones in some regions do not support ALB but that's not documented anywhere. I was able to work around the issue by configuring the ALB to use ap-northeast-1c and ap-northeast-1b (in that order!).

You should modify your ECS settings to use AZ 1c first then AZ 1b but not AZ 1a.