Docker Cookbook

6.2 Starting a Container on CoreOS via cloud-init | 173

---

$ docker ps
CONTAINER ID IMAGE COMMAND ...
fa9ff4f2234c dockerfile/elasticsearch:latest "/elasticsearch/bin/ ...
Find the IP address of the virtual machine on the host-only interface (i.e., 
eth1
) and
open your browser or 
curl
at that address on port 9200:
$ curl -s http://172.17.8.101:9200 | python -m json.tool
{
"cluster_name": "elasticsearch",
"name": "Wyatt Wingfoot",
"status": 200,
"tagline": "You Know, for Search",
"version": {
"build_hash": "89d3241d670db65f994242c8e8383b169779e2d4",
"build_snapshot": false,
"build_timestamp": "2014-10-26T15:49:29Z",
"lucene_version": "4.10.2",
"number": "1.4.1"
}
}
Congratulations—you are running one 
Elasticsearch
container on a CoreOS instance,
specifying it as a 
systemd
unit file via 
cloud-init
.
Discussion
The 
user-data
file present in the 
coreos-vagrant
repository is used by CoreOS to
configure the instance using the CoreOS version of 
cloud-init
. 
cloud-init
is used
by most public cloud providers and supported by most infrastructure as a service
software solution to contextualize the virtual machine instances started in the cloud
at boot time. The interesting part in this recipe is that a container is defined as a 
sys
temd
unit file and started on boot. CoreOS has some official 
documentation
about
this.
CoreOS has its own implementation of 
cloud-init
. Some 
cloud-
init
operations may not be supported, and others are valid for
only CoreOS (e.g., 
fleet
, 
etcd
, 
flannel
).