Method of finding instances attached to ELB - amazon-ec2

Question

I am using the Amazon AWS ELB command line tools. Is there a way of finding out the instances attached to a particular Elastic Load Balancer (ELB)?

Answer 1

2013/12/18: To update this and since the links are dead!
I installed the new AWS cli tools:
$ pip install awscli
Then ran:
$ aws configure
AWS Access Key ID [None]: my-key
AWS Secret Access Key [None]: my-secret
Default region name [None]: us-east-1
Default output format [None]:
This data is saved into ~/.aws/config.
Then I can find instances connected to a loadbalancer like so:
$ aws elb describe-load-balancers --load-balancer-name "my-name"
{
"LoadBalancerDescriptions": [
{
"Subnets": [],
"CanonicalHostedZoneNameID": "ID",
"CanonicalHostedZoneName": "my-name-foo.us-east-1.elb.amazonaws.com",
"ListenerDescriptions": [
{
"Listener": {
"InstancePort": 80,
"LoadBalancerPort": 80,
"Protocol": "HTTP",
"InstanceProtocol": "HTTP"
},
"PolicyNames": []
},
{
"Listener": {
"InstancePort": 80,
"SSLCertificateId": "arn:aws:iam::x:server-certificate/x-ssl-prod",
"LoadBalancerPort": 443,
"Protocol": "HTTPS",
"InstanceProtocol": "HTTP"
},
"PolicyNames": [
"AWSConsole-SSLNegotiationPolicy-api-production"
]
}
],
"HealthCheck": {
"HealthyThreshold": 10,
"Interval": 30,
"Target": "HTTP:80/healthy.php",
"Timeout": 5,
"UnhealthyThreshold": 2
},
"BackendServerDescriptions": [],
"Instances": [
{
"InstanceId": "i-FIRST-INSTANCEID"
},
{
"InstanceId": "i-SECOND-INSTANCEID"
}
],
"DNSName": "my-name-foo.us-east-1.elb.amazonaws.com",
"SecurityGroups": [],
"Policies": {
"LBCookieStickinessPolicies": [],
"AppCookieStickinessPolicies": [],
"OtherPolicies": [
"AWSConsole-SSLNegotiationPolicy-my-name"
]
},
"LoadBalancerName": "my-name",
"CreatedTime": "2013-08-05T16:55:22.630Z",
"AvailabilityZones": [
"us-east-1d"
],
"Scheme": "internet-facing",
"SourceSecurityGroup": {
"OwnerAlias": "amazon-elb",
"GroupName": "amazon-elb-sg"
}
}
]
}
The data is in LoadBalancerDescriptions.Instances.
My loadbalancer is called my-name — this is the name you selected when you created it.
Old answer below!
I'm not familiar with the cli tool, but I used the API.
I'd check these two requests:
DescribeLoadBalancers
DescribeInstanceHealth
The cli tool probably has something to resemble these?
HTH!

Answer 2

Assuming you have aws-cli and jq installed, you can use the following command to get associated ec2 instance ids:
aws elb describe-load-balancers --load-balancer-name my-elb \
| jq -r '.LoadBalancerDescriptions[].Instances[].InstanceId'
This will return the ec2 ids associated with that ELB.
Side note: I recommend you setup aws cli profiles so you don't have to fiddle with environment variables and region params (as much).

Answer 3

Because I love answers that can be used with a minimum of search/replace and copy paste
Prerequisites : aws-cli configured
pip install awscli
aws configure
Configure : your ELB name
$ELB_NAME = "Your-elb-name"
Copy-n-Paste in terminal
for ID in $(aws elb describe-load-balancers --load-balancer-name $ELB_NAME \
--query LoadBalancerDescriptions[].Instances[].InstanceId \
--output=text);
do
aws ec2 describe-instances --instance-ids $ID \
--query Reservations[].Instances[].PublicIpAddress \
--output text
done
Will output a list of Public IPs. You could also just execute the query inside the parenthesis of the for ID in $(...) to just get the instance IDs
Want something different ?
Feel free to have a look at the structure of
aws elb describe-load-balancers --load-balancer-name $ELB_NAME
aws ec2 describe-instances --instance-ids $INSTANCE_ID
and change the query accordingly!

Answer 4

If anyone arrives here from a search as to why the elb-describe-lbs command returns nothing when they have ELBs up and running, what I realised was I needed to add EC2_REGION=eu-west-1 to my environment variables (or use elb-describe-lbs --region command)

Answer 5

If you want to see all your ELB's and the instances attached use JMESPath like this:
aws elb describe-load-balancers --query "LoadBalancerDescriptions[*].{ID:LoadBalancerName,InstanceId:Instances[*].InstanceId}[*]. {ELB:ID,InstanceId:InstanceId[*]}" --output=json
Result
[
{
"ELB": "my_name",
"InstanceId": [
"i-0cc72"
]
},
{
"ELB": "my_name2",
"InstanceId": [
"i-02ff5f",
"i-09e467"
]
}
]
If you know the name of the ELB and want to see what is attached use JMESPath like this:
aws elb describe-load-balancers --load-balancer-name "my_name" --query "LoadBalancerDescriptions[].{ID:LoadBalancerName,InstanceId:Instances[].InstanceId}[].{ELB:ID,InstanceId:InstanceId[]}" --output=json
Result:
[
{
"ELB": "my_name",
"InstanceId": [
"i-02ff5f72",
"i-09e46743"
]
}
]

Answer 6

replace INSTANCEID with actual instance id
aws elb describe-load-balancers --query "LoadBalancerDescriptions[*].{ID:LoadBalancerName,InstanceId:Instances[?InstanceId=='INSTANCEID'].InstanceId}[*].{ID:ID,InstanceId:InstanceId[0]}" --output=text | grep INSTANCEID | awk '{print $1}'

Answer 7

In node.js you can do this by using aws-sdk.
var AWS = require('aws-sdk')
var options = {
accessKeyId: 'accessKeyId',
secretAccessKey: 'secretAccessKey',
region: 'region'
}
var elb = new AWS.ELB(options)
elb.describeLoadBalancers({LoadBalancerNames: ['elbName']}, function(err, data) {
if (err) {
console.log('err: ', err)
}
else {
console.log('data: ', data.LoadBalancerDescriptions)
}
})
data.LoadBalancerDescriptions is an array and each element in the array is an object with the property Instances that has the instance id.

Answer 8

You can loop trough all you load balancer instance ids as follows:
while read -r lb ; do echo -e "\n\n start lb: $lb " ; \
echo run cmd on lb: $lb ; echo " stop lb: $lb" ; \
done < <(aws elb describe-load-balancers --query \
'LoadBalancerDescriptions[].Instances[].InstanceId' \
--profile dev|perl -nle 's/\s+/\n/g;print')
You can loop trough your load balancers names as follows :
# how-to loop trough all your load balancer names
while read -r lb ; do \
echo -e "\n\n start lb: $lb " ; \
echo run cmd on lb: $lb ; \
echo " stop lb: $lb" ; \
done < <(aws elb describe-load-balancers --query \
'LoadBalancerDescriptions[].LoadBalancerName' \
--profile rnd|perl -nle 's/\s+/\n/g;print')
Provided that you have configured your aws cli :
src: http://docs.aws.amazon.com/cli/latest/topic/config-vars.html
cat << "EOF" > ~/.aws/config
[profile dev]
output = text
region = us-east-1
[profile dev]
output = text
region = us-east-1
[default]
output = text
region = Global
EOF
And configured your security credentials:
# in aws admin console :
# Services => iam => users => <<your_username>> => Security Credentials => Access Keys
# configure the aws cli
cat << "EOF" > ~/.aws/credentials
[dev]
aws_access_key_id = <<your_aws_access_key_id_in_the_dev_environment>>
aws_secret_access_key = <<your_aws_secret_access_key_in_dev_env>>
[dev]
aws_access_key_id = <<your_aws_access_key_id_in_the_dev_environment>>
aws_secret_access_key = <<your_aws_secret_access_key_in_dev_env>>
[default]
aws_access_key_id = <<your_aws_access_key_id_in_the_dev_environment>>
aws_secret_access_key = <<your_aws_secret_access_key_in_dev_env>>
EOF

Answer 9

aws elb describe-load-balancers --load-balancer-name "LB_NAME" | grep "InstanceId" | awk '{print $2}' | sed 's/\"//g'

Answer 10

First do elb-describe-lbs to get a list of your load balancers and their names.
Then do elb-describe-instance-health <LB_NAME> to get a list of instances behind that load balancer. LB_NAME is the value of the 2nd column in the output of elb-describe-lbs.

Answer 11

You can use AWS command line tools with some bash piping:
elb-describe-instance-health loadbalancer_name --region eu-west-1 | awk '{ print $2 }' | xargs ec2-describe-instances --region eu-west-1 | grep ^INSTANCE | awk '{ print $4 }'
This will give you the public DNS name for every instance attached to the ELB, you can change the awk columns respectively to get other details.