Health checks failed with these code :[404]

Question

Application load balancer
For one az it's showing healthy
For other az it's showing below error
Health checks failed with these code :[404]

Gary Mclean · Accepted Answer

404 is page not found. What ever your target group has configured for health check is finding the page in all the good az’s but the page doesn’t exist on the end machine that’s returning 404.

As suggested your instance is setup differently. Check  it’s running same configs on the webserver, all the pages exist, the file system has the correct permissions etc.

This is a host issue and not alb issue.

Didier_Durand · Answer

Hi, this error probably means that the processing instances (EC2, ECS / Fargate, etc.) responding to health check in each AZ are not configured strictly identically. You should compare the configs of those instances in different AZs in all details to see where the discrepancy is.

Hiroki Takahashi · Answer

Hi.This docunent will help you to identify cause of failing healthcheck in other az.

https://repost.aws/knowledge-center/elb-fix-failing-health-checks-alb

Health checks failed with these code :[404]

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