how to get private IP of EC 2 dynamically and put it in /etc/hosts
Solution 1
I had a similar need for a database cluster (some sort of poor's man Consul alternative), I ended using the following Terraform file:
variable "cluster_member_count" {
description = "Number of members in the cluster"
default = "3"
}
variable "cluster_member_name_prefix" {
description = "Prefix to use when naming cluster members"
default = "cluster-node-"
}
variable "aws_keypair_privatekey_filepath" {
description = "Path to SSH private key to SSH-connect to instances"
default = "./secrets/aws.key"
}
# EC2 instances
resource "aws_instance" "cluster_member" {
count = "${var.cluster_member_count}"
# ...
}
# Bash command to populate /etc/hosts file on each instances
resource "null_resource" "provision_cluster_member_hosts_file" {
count = "${var.cluster_member_count}"
# Changes to any instance of the cluster requires re-provisioning
triggers {
cluster_instance_ids = "${join(",", aws_instance.cluster_member.*.id)}"
}
connection {
type = "ssh"
host = "${element(aws_instance.cluster_member.*.public_ip, count.index)}"
user = "ec2-user"
private_key = "${file(var.aws_keypair_privatekey_filepath)}"
}
provisioner "remote-exec" {
inline = [
# Adds all cluster members' IP addresses to /etc/hosts (on each member)
"echo '${join("\n", formatlist("%v", aws_instance.cluster_member.*.private_ip))}' | awk 'BEGIN{ print \"\\n\\n# Cluster members:\" }; { print $0 \" ${var.cluster_member_name_prefix}\" NR-1 }' | sudo tee -a /etc/hosts > /dev/null",
]
}
}
One rule is that each cluster member get named by the cluster_member_name_prefix
Terraform variable followed by the count index (starting at 0): cluster-node-0, cluster-node-1, etc.
This will add the following lines to each "aws_instance.cluster_member" resource's /etc/hosts
file (the same exact lines and in the same order for every member):
# Cluster members:
10.0.1.245 cluster-node-0
10.0.1.198 cluster-node-1
10.0.1.153 cluster-node-2
In my case, the null_resource
that populates the /etc/hosts
file was triggered by an EBS volume attachment, but a "${join(",", aws_instance.cluster_member.*.id)}"
trigger should work just fine too.
Also, for local development, I added a local-exec
provisioner to locally write down each IP in a cluster_ips.txt
file:
resource "null_resource" "write_resource_cluster_member_ip_addresses" {
depends_on = ["aws_instance.cluster_member"]
provisioner "local-exec" {
command = "echo '${join("\n", formatlist("instance=%v ; private=%v ; public=%v", aws_instance.cluster_member.*.id, aws_instance.cluster_member.*.private_ip, aws_instance.cluster_member.*.public_ip))}' | awk '{print \"node=${var.cluster_member_name_prefix}\" NR-1 \" ; \" $0}' > \"${path.module}/cluster_ips.txt\""
# Outputs is:
# node=cluster-node-0 ; instance=i-03b1f460318c2a1c3 ; private=10.0.1.245 ; public=35.180.50.32
# node=cluster-node-1 ; instance=i-05606bc6be9639604 ; private=10.0.1.198 ; public=35.180.118.126
# node=cluster-node-2 ; instance=i-0931cbf386b89ca4e ; private=10.0.1.153 ; public=35.180.50.98
}
}
And, with the following shell command I can add them to my local /etc/hosts
file:
awk -F'[;=]' '{ print $8 " " $2 " #" $4 }' cluster_ips.txt >> /etc/hosts
Example:
35.180.50.32 cluster-node-0 # i-03b1f460318c2a1c3
35.180.118.126 cluster-node-1 # i-05606bc6be9639604
35.180.50.98 cluster-node-2 # i-0931cbf386b89ca4e
Solution 2
Terraform provisioners expose a self
syntax for getting data about the resource being created.
If you were just interested in the instance being created's private IP address you could use ${self.private_ip}
to get at this.
Unfortunately if you need to get the IP addresses of multiple sub-resources (eg ones created by using the count
meta attribute) then you will need to do this outside of the resource's provisioner using the null_resource
provider.
The resource provider docs show a good use case for this:
resource "aws_instance" "cluster" {
count = 3
...
}
resource "null_resource" "cluster" {
# Changes to any instance of the cluster requires re-provisioning
triggers {
cluster_instance_ids = "${join(",", aws_instance.cluster.*.id)}"
}
# Bootstrap script can run on any instance of the cluster
# So we just choose the first in this case
connection {
host = "${element(aws_instance.cluster.*.public_ip, 0)}"
}
provisioner "remote-exec" {
# Bootstrap script called with private_ip of each node in the clutser
inline = [
"bootstrap-cluster.sh ${join(" ", aws_instance.cluster.*.private_ip)}",
]
}
}
but in your case you probably want something like:
resource "aws_instance" "ceph-cluster" {
...
}
resource "null_resource" "ceph-cluster" {
# Changes to any instance of the cluster requires re-provisioning
triggers {
cluster_instance_ids = "${join(",", aws_instance.ceph-cluster.*.id)}"
}
connection {
host = "${element(aws_instance.cluster.*.public_ip, count.index)}"
}
provisioner "remote-exec" {
inline = [
"cat /etc/hosts",
"cat ~/scripts/ceph/ceph_rsa.pub >> ~/.ssh/authorized_keys",
"cp -arp ~/scripts/ceph/ceph_rsa ~/.ssh/ceph_rsa",
"chmod 700 ~/.ssh/ceph_rsa",
"echo 'IdentityFile ~/.ssh/ceph_rsa' >> ~/.ssh/config",
"echo 'User ubuntu' >> ~/.ssh/config",
"echo '${aws_instance.ceph-cluster.0.private_ip} node01 ceph01' >> /etc/hosts ",
"echo '${aws_instance.ceph-cluster.1.private_ip} node02 ceph02' >> /etc/hosts "
]
}
}
Solution 3
This could be a piece of cake with Terrafrom/Sparrowform. No need in null_resources, with the minimum of fuss:
Bootstrap infrastructure
$ terrafrom apply
Prepare Sparrowform privision scenario to insert ALL nodes public ips / dns names into every node's /etc/hosts file
$ cat sparrowfile
#!/usr/bin/env perl6
use Sparrowform;
my @hosts = (
"127.0.0.1 localhost localhost.localdomain localhost4 localhost4.localdomain4",
"::1 localhost localhost.localdomain localhost6 localhost6.localdomain6"
);
for tf-resources() -> $r {
my $rd = $r[1]; # resource data
next unless $rd<public_ip>;
next unless $rd<public_dns>;
next if $rd<public_ip> eq input_params('Host');
push @hosts, $rd<public_ip> ~ ' ' ~ $rd<public_dns>;
}
file '/etc/hosts', %(
action => 'create',
content => @hosts.join("\n")
);
Give it a run, Sparrowform will execute scenario on every node
$ sparrowform --bootstrap --ssh_private_key=~/.ssh/aws.key --ssh_user=ec2-user
PS. disclosure - I am the tool author
Comments
-
negabaro almost 2 years
I would like to create multiple EC2 instances using Terraform and write the private IP addresses of the instances to
/etc/hosts
on every instance.Currently I am trying the following code but it's not working:
resource "aws_instance" "ceph-cluster" { count = "${var.ceph_cluster_count}" ami = "${var.app_ami}" instance_type = "t2.small" key_name = "${var.ssh_key_name}" vpc_security_group_ids = [ "${var.vpc_ssh_sg_ids}", "${aws_security_group.ceph.id}", ] subnet_id = "${element(split(",", var.subnet_ids), count.index)}" associate_public_ip_address = "true" // TODO 一時的にIAM固定 //iam_instance_profile = "${aws_iam_instance_profile.app_instance_profile.name}" iam_instance_profile = "${var.iam_role_name}" root_block_device { delete_on_termination = "true" volume_size = "30" volume_type = "gp2" } connection { user = "ubuntu" private_key = "${file("${var.ssh_key}")}" agent = "false" } provisioner "file" { source = "../../../scripts" destination = "/home/ubuntu/" } tags { Name = "${var.infra_name}-ceph-cluster-${count.index}" InfraName = "${var.infra_name}" } provisioner "remote-exec" { inline = [ "cat /etc/hosts", "cat ~/scripts/ceph/ceph_rsa.pub >> ~/.ssh/authorized_keys", "cp -arp ~/scripts/ceph/ceph_rsa ~/.ssh/ceph_rsa", "chmod 700 ~/.ssh/ceph_rsa", "echo 'IdentityFile ~/.ssh/ceph_rsa' >> ~/.ssh/config", "echo 'User ubuntu' >> ~/.ssh/config", "echo '${aws_instance.ceph-cluster.0.private_ip} node01 ceph01' >> /etc/hosts ", "echo '${aws_instance.ceph-cluster.1.private_ip} node02 ceph02' >> /etc/hosts " ] } } aws_instance.ceph-cluster. *. private_ip
I would like to get the result of the above command and put it in
/etc/hosts
.