RabbitMQ Cluster With Terraform On AWS

Konrad Rotkiewicz
31 July 2017 · 7 min read

Creating RabbitMQ cluster is tricky. It is easy to do manually and hard if you’d like to automate it.

TL;DR Use this Terraform configuration to create RabbitMQ cluster in less than 5 minutes.

The simplest cluster requires 2 nodes and a load balancer. In AWS we are going to use ELB as a load balancer and put nodes in Auto Scaling group, so that if a node goes down (or became unhealthy) it will be replaced by a new one.

Our setup will be:

rabbitmq

Using Terraform we can create Launch Configuration, Auto Scaling group and ELB. This is our ELB configuration:

resource "aws_elb" "elb" {
name = "rabbit-elb"
listener {
instance_port = 5672
instance_protocol = "tcp"
lb_port = 5672
lb_protocol = "tcp"
}
listener {
instance_port = 15672
instance_protocol = "http"
lb_port = 80
lb_protocol = "http"
}
health_check {
interval = 30
unhealthy_threshold = 10
healthy_threshold = 2
timeout = 3
target = "TCP:5672"
}
subnets = ["${var.subnet_ids}"]
idle_timeout = 3600
internal = true
security_groups = ["${aws_security_group.rabbitmq_elb.id}"]
tags {
Name = "rabbitmq"
}
}
view raw elb.tf hosted with ❤ by GitHub

ELB is configured to replace a node if it becomes unhealthy after 5 minutes (there are 10 checks every 30 seconds). It listens on ports 5672 (AMQP) and 80 proxied to 15672 (HTTP interface).

What about nodes ? We use cloud-init to initialize a node and in there we configure RabbitMQ to run in Docker.

After RabbitMQ is running, the node has to join the cluster. To do that we call rabbitmqctl join_cluster <node> for each of the nodes.

To find out what are the other nodes in the cluster we prepared a bash script that query nodes in our Auto Scaling group:

#!/usr/bin/env bash
export AWS_DEFAULT_REGION='${region}'
DNSES=$(aws ec2 describe-instances --filters "Name=tag:aws:autoscaling:groupName,Values=rabbitmq" "Name=instance-state-name,Values=running" | jq ".Reservations[].Instances[].PrivateDnsName" | xargs)
HOSTNAMES=()
for dns in $DNSES; do
hostname=($${dns//./ })
if [ "$hostname" != "$HOSTNAME" ]; then
HOSTNAMES+=( $hostname )
fi
done
echo $HOSTNAMES
view raw 1.sh hosted with ❤ by GitHub

And then a script to join to these nodes:

#!/usr/bin/env sh
HOSTNAMES=( $@ )
for run in {1..3}; do
sleep $[ ( $RANDOM % 10 ) + 1 ]s
rabbitmqctl stop_app
NEW_HOSTNAMES=()
for hostname in $HOSTNAMES; do
rabbitmqctl join_cluster rabbit@$hostname
st=$?
if [ $st -ne 0 ] && [ $st -ne 130 ]; then # 130 is "already joined"
NEW_HOSTNAMES+=( $hostname )
fi
done
HOSTNAMES=( $${NEW_HOSTNAMES[@]} )
rabbitmqctl start_app
if [ $${#HOSTNAMES[@]} -eq 0 ]; then
exit 0
fi
done
view raw 2.sh hosted with ❤ by GitHub

The tricky part here is that to join a cluster, you have to stop the node first. So there is a chance that other node could also be stopped as well. To mitigate this problem we set sleep for some random amount of seconds before stopping the server Also, in case of errors, we perform sane amount of retries.

Last thing that requires explanation is that querying nodes in given Auto Scalinggroup. To to be able to do so you need to associate _IAM_ role with autoscaling:DescribeAutoScalingInstances and ec2:DescribeInstancespolicies. This can be done by our Terraform configuration automatically:

resource "aws_iam_role" "role" {
name = "rabbitmq"
assume_role_policy = "${data.aws_iam_policy_document.policy_doc.json}"
}
resource "aws_iam_role_policy" "policy" {
name = "rabbitmq"
role = "${aws_iam_role.role.id}"
policy = <<EOF
{
"Version": "2012-10-17",
"Statement": [
{
"Effect": "Allow",
"Action": [
"autoscaling:DescribeAutoScalingInstances",
"ec2:DescribeInstances"
],
"Resource": [
"*"
]
}
]
}
EOF
}
resource "aws_iam_instance_profile" "profile" {
name = "rabbitmq"
role = "${aws_iam_role.role.name}"
}
view raw iam.tf hosted with ❤ by GitHub

Using this Terraform configuration we successfully deployed many RabbitMQ clusters with up to 4 nodes.

Leave a comment if you find this useful or a question in case of troubles. Cheers!

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