Place an instance exclusively into an AWS LB Target Group

activate-target.sh

#!/bin/bash

set -euo pipefail

function log {
  echo "$(date +%T): $@"
}

tgname=$1
iid=$2

log "Getting ARN for Target Group '$tgname'..."

# Find tg ARN
target_group=$(aws elbv2 describe-target-groups \
  --no-paginate \
  --names "$tgname" \
  --query "TargetGroups[0].TargetGroupArn" \
  --output text)

log "Adding instance '$iid' to Target Group '$target_group'"

# add instance to target group
aws elbv2 register-targets \
  --target-group-arn "$target_group" \
  --targets Id="$iid"

log "Added instance '$iid' to Target Group '$target_group'"

# List instances in TG, excluding the new one just added
old_iids=$(aws elbv2 describe-target-health \
  --target-group-arn "$target_group" \
  --query 'TargetHealthDescriptions[].Target[].Id|join(`\n`, @)' \
  --output text | grep -v "$iid")

log "Removing instances: $old_iids"

remove_iids=
for i in $old_iids; do
  remove_iids="$remove_iids Id=$i"
done

# deregister old ones, joined with Id=
aws elbv2 deregister-targets \
  --target-group-arn "$target_group" \
  --targets $remove_iids

log "Removal complete"