Docker Cookbook

224 | Chapter 7: The Docker Ecosystem: Tools

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Open your browser at 
http://192.168.33.10:5050
to access the Mesos UI, and then
open your browser at 
http://192.168.33.10:8080
to access the Marathon UI.
To start an Nginx container in that Mesos cluster, create a Mesos application in the
Marathon framework using the API:
$ curl -si -H 'Content-Type: application/json' \
-d @docker.json 192.168.33.10:8080/v2/apps
Once the image has been downloaded, you can access the Nginx welcome screen in a
similar fashion as described in 
Recipe 7.11
.
The 
docker.json
application definition specifies 128 MB of RAM. If
your slaves do not have enough memory, the application could be
stuck in 
deploying
stage. Make sure that your slaves have enough
RAM or reduce the memory constraints of your application.
Discussion
The inventory used by Ansible is harcoded in the 
inventory
file. If you change the IP
address of the nodes or add more nodes, make sure to update the inventory as well.
The current play executes 
docker run
commands remotely over SSH. If you want to
use the Ansible Docker module, comment the 
command
tasks and uncomment the
docker
tasks.
You will notice that the Mesos slave runs as a container. When starting the container,
you pass the environment variable 
MESOS_CONTAINERIZERS=docker,mesos
, which
configures the slave to use Docker. The slave will start other containers on the host
itself. This is achieved by mounting 
/var/run/docker.sock
, 
/usr/bin/docker
, and 
/sys
from the host to the container. Although it works in the testing scenario, the Mesos
containerizer is not made to do this. You should consider running the slave on the
hosts themselves until Mesos development recommends running the slave in contain‐
ers for production.