Docker Cookbook

6.3 Starting a CoreOS Cluster via Vagrant to Run Containers on Multiple Hosts | 175

---

In the 
config.rb
file, uncomment the beginning of the script and set your number of
instances so that it looks like this:
if
File
.
exists?
(
'user-data'
)
&&
ARGV
[
0
].
eql?
(
'up'
)
require
'open-uri'
require
'yaml'
token
=
open
(
'https://discovery.etcd.io/new'
)
.
read
data
=
YAML
.
load
(
IO
.
readlines
(
'user-data'
)
[
1
.
.
-
1
].
join
)
data
[
'coreos'
][
'etcd'
][
'discovery'
]
=
token
yaml
=
YAML
.
dump
(
data
)
File
.
open
(
'user-data'
,
'w'
)
{
|
file
|
file
.
write
(
"#cloud-config\n\n
#{
yaml
}
"
)
}
end
.
.
.
$num_instances
=
4
If you have followed 
Recipe 6.1
 and 
Recipe 6.2
, destroy any existing
CoreOS instances before booting your cluster with 
vagrant
destroy
.
With your number of instances set to four, make sure you have copied the original
user-data.sample
to a 
user-data
file and then simply 
vagrant up
and wait for the pro‐
visioning to finish. You can then 
ssh
to one of the nodes and use a new tool, 
fleet
, to
list the machines that have joined the cluster:
$ cp user-data.sample user-data
$ vagrant up
$ vagrant status
Current machine states:
core-01 running (virtualbox)
core-02 running (virtualbox)
core-03 running (virtualbox)
core-04 running (virtualbox)
$ vagrant ssh core-01
CoreOS (stable)
core@core-01 ~ $ fleetctl list-machines
MACHINE IP METADATA
01efec94... 172.17.8.102 -
3602cd04... 172.17.8.104 -
cd3de202... 172.17.8.103 -
e4c0e706... 172.17.8.101 -
176 | Chapter 6: Optimized Operating System Distributions for Docker

---

Discussion
The 
etcd
discovery service provided by CoreOS is used to boostrap the cluster (i.e.,
defining a leader). In the 
user-data
file, you can now see a line that defines the 
discov
ery
key and contains a token (your token will be different than the one listed here):
discovery: https://discovery.etcd.io/61297b379e5024f33b57bd7e7225d7d7
If you 
curl
this URL (
curl -s https://discovery.etcd.io/
61297b379e5024f33b57bd7e7225d7d7 | python -m json.tool
), you will see the IPs
of the nodes in your cluster. Anyone who obtains access to your token could obtain a
list of your cluster nodes and try to add one of his nodes in your cluster, so handle
with care:
{
"createdIndex"_:_279743993_,_"dir"_:_true'>"action"
:
"get"
,
"node"
:
{
"createdIndex"
:
279743993
,
"dir"
:
true
,
"key"
:
"/_etcd/registry/61297b379e5024f33b57bd7e7225d7d7"
,
"modifiedIndex"
:
279743993
,
"nodes"
:
[
{
"createdIndex"
:
279744808
,