CODEWITHSUNDEEP
amazon-web-servicesamazon-elbhealth-check
Ciprian Stoica
Ciprian Stoica

Reputation: 2439

High number of aws target group health checks

I have an application load balancer with several registered target groups (and 6 availability zones in case it is important to mention).

There is one ec2 instance which is the registered target for all target groups. On the ec2 instance there is an nginx running.

For each target group I defined a health check with a custom url and with an interval of 60 seconds.

When I look at the nginx logs I expect to see the health check url for a particular target group every 60 seconds. But to my surprise I see that in 60 seconds there are groups of 8 calls like this:

172.31.25.32 - - [14/Feb/2022:16:00:29 +0000] "GET /path/target-group-X/ HTTP/1.1" 200 4 "-" "ELB-HealthChecker/2.0" rt=0.118 uct="0.000" uht="0.120" urt="0.120"
172.31.89.13 - - [14/Feb/2022:16:00:35 +0000] "GET /path/target-group-X/ HTTP/1.1" 200 4 "-" "ELB-HealthChecker/2.0" rt=0.080 uct="0.000" uht="0.080" urt="0.080"
172.31.75.210 - - [14/Feb/2022:16:00:43 +0000] "GET /path/target-group-X/ HTTP/1.1" 200 4 "-" "ELB-HealthChecker/2.0" rt=0.050 uct="0.000" uht="0.052" urt="0.052"
172.31.88.219 - - [14/Feb/2022:16:00:44 +0000] "GET /path/target-group-X/ HTTP/1.1" 200 4 "-" "ELB-HealthChecker/2.0" rt=0.059 uct="0.000" uht="0.060" urt="0.060"
172.31.9.236 - - [14/Feb/2022:16:00:51 +0000] "GET /path/target-group-X/ HTTP/1.1" 200 4 "-" "ELB-HealthChecker/2.0" rt=0.059 uct="0.000" uht="0.060" urt="0.060"
172.31.15.138 - - [14/Feb/2022:16:01:02 +0000] "GET /path/target-group-X/ HTTP/1.1" 200 4 "-" "ELB-HealthChecker/2.0" rt=0.010 uct="0.000" uht="0.008" urt="0.008"
172.31.49.23 - - [14/Feb/2022:16:01:07 +0000] "GET /path/target-group-X/ HTTP/1.1" 200 4 "-" "ELB-HealthChecker/2.0" rt=0.062 uct="0.000" uht="0.064" urt="0.064"
172.31.47.189 - - [14/Feb/2022:16:01:13 +0000] "GET /path/target-group-X/ HTTP/1.1" 200 4 "-" "ELB-HealthChecker/2.0" rt=0.094 uct="0.000" uht="0.092" urt="0.092"


172.31.25.32 - - [14/Feb/2022:16:01:29 +0000] "GET /path/target-group-X/ HTTP/1.1" 200 4 "-" "ELB-HealthChecker/2.0" rt=0.050 uct="0.000" uht="0.048" urt="0.048"
172.31.89.13 - - [14/Feb/2022:16:01:35 +0000] "GET /path/target-group-X/ HTTP/1.1" 200 4 "-" "ELB-HealthChecker/2.0" rt=0.049 uct="0.000" uht="0.048" urt="0.048"
172.31.75.210 - - [14/Feb/2022:16:01:43 +0000] "GET /path/target-group-X/ HTTP/1.1" 200 4 "-" "ELB-HealthChecker/2.0" rt=0.280 uct="0.000" uht="0.280" urt="0.280"
172.31.88.219 - - [14/Feb/2022:16:01:44 +0000] "GET /path/target-group-X/ HTTP/1.1" 200 4 "-" "ELB-HealthChecker/2.0" rt=0.050 uct="0.000" uht="0.048" urt="0.048"
172.31.9.236 - - [14/Feb/2022:16:01:52 +0000] "GET /path/target-group-X/ HTTP/1.1" 200 4 "-" "ELB-HealthChecker/2.0" rt=0.508 uct="0.000" uht="0.508" urt="0.508"
172.31.15.138 - - [14/Feb/2022:16:02:02 +0000] "GET /path/target-group-X/ HTTP/1.1" 200 4 "-" "ELB-HealthChecker/2.0" rt=0.176 uct="0.000" uht="0.172" urt="0.172"
172.31.49.23 - - [14/Feb/2022:16:02:07 +0000] "GET /path/target-group-X/ HTTP/1.1" 200 4 "-" "ELB-HealthChecker/2.0" rt=0.061 uct="0.000" uht="0.060" urt="0.060"
172.31.47.189 - - [14/Feb/2022:16:02:13 +0000] "GET /path/target-group-X/ HTTP/1.1" 200 4 "-" "ELB-HealthChecker/2.0" rt=0.057 uct="0.000" uht="0.056" urt="0.056"

There are 8 different local IP-s from which the calls are coming. If I take each such IP separately (e.g. 172.31.25.32), then indeed the health checks calls from that IP are arriving after exactly 60 seconds. But what is about the other calls? Why are so many?

Upvotes: 0

Views: 1343

Answers (1)

Mark B
Mark B

Reputation: 200682

I think at a minimum the target group is going to do a health check from each availability zone, or maybe each VPC subnet. You can probably map those IPs back to specific subnets in your VPC.

It definitely seems excessive, but you have to realize that behind the scenes a multi-az load balancer is really multiple servers, and each one is doing its own health check against your target server(s).

Upvotes: 2

Related Questions