ALB Listener Rule, weighted Target Groups

.tf

resource "aws_alb_listener_rule" "http_80" {
  count = local.lb ? 1 : 0
  listener_arn = data.aws_alb_listener.http_80.arn
  action {
    type = "forward"
    target_group_arn = aws_alb_target_group.http_80[0].arn
  }
  condition {
    host_header {
      values = [local.host_name]
    }
  }
  // todo: terraform does not yet support weighted target groups
  provisioner "local-exec" {
    command = local.blue_green ? "${path.module}/add_target_groups_to_listener_rule.sh ${data.aws_region.current.name} ${data.aws_alb_listener.http_80.arn} ${self.arn} ${aws_alb_target_group.http_80[1].arn}" : "echo"
  }
  lifecycle {
    ignore_changes = [action.0.target_group_arn]
  }
}

add_target_groups_to_listener_rule.sh

#!/bin/bash
set -eo pipefail

aws_region=$1
listener_arn=$2
rule_arn=$3
tg_http_80_1_arn=$4

rules=$(aws elbv2 describe-rules --region $aws_region --listener-arn $listener_arn)
rule=$(echo $rules | jq --arg rule_arn "$rule_arn" '.Rules[] | select(.RuleArn == $rule_arn)')
expr_fwdcfg='.Actions[.Actions | map(.Type=="forward") | index(true)].ForwardConfig'
rule=$(echo $rule | jq --arg tg_arn "$tg_http_80_1_arn" "$expr_fwdcfg"'
  .TargetGroups += [{
    "TargetGroupArn": $tg_arn,
    "Weight": 0
  }]')
rule=$(echo $rule | jq "$expr_fwdcfg"'
  .TargetGroupStickinessConfig = {
    "Enabled": true,
    "DurationSeconds": 86400
  }')
rule=$(echo $rule | jq 'del(.Priority)
  | del(.IsDefault)
  | (.Conditions |= map(del(.Values)))
  | (.Actions |= map(del(.TargetGroupArn)))')
echo "rule=$rule"
aws elbv2 modify-rule --region $aws_region --rule-arn $rule_arn --cli-input-json "$rule"